Abstract
A simple method for the synthesis of 3-arylbenzophosphole oxides under Suzuki–Miyaura coupling conditions has been presented. It employs benzophosphol-3-yl triflate starting materials which, prior to our work, had not been used for the synthesis of 3-arylbenzophosphole oxides. The reactions proceed over 24 h and provide a library of 3-arylbenzophosphole oxides. The synthetic access to the benzophosphol-3-yl triflates has been improved. The preliminary photophysical properties of some 3-arylbenzophosphole oxides have been investigated by absorption and emission measurements. The theoretical calculations were performed to establish structure–property relationships.
Introduction
Benzo[b]phosphole oxides have recently become important in the chemistry of organic materials because they have well-established semiconducting, fluorescent, and coordinating properties that have led to uses in processes as diverse as organic electronics, bioimaging, coordination chemistry, and catalysis.1 Historically, however, they have been much less thoroughly explored than many other heterocyclic compounds.2 Conventional syntheses of benzo[b]phosphole rings generally involve improvements to the protocol pioneered by Winter and Butters,3 and rely on base-mediated intramolecular cyclization of (2-alkynylphenyl)phenylarylphosphine derivatives (Scheme 1A).4 Modern routes to benzophospholes that are decorated with aryl substituents can be divided into several classes (Scheme 1B–D). The first is based on oxidative annulation in the presence of a metal-based oxidant (silver,5 manganese,5a,5b copper6 compounds, or others7) (Scheme 1B). A second method involves a one-pot multicomponent reaction using aryl organozinc or Grignard reagents (Scheme 1C).8 A third approach, proposed by Miura and Satoh in 2016, involves ortho-alkenylation of arylthiophosphinamides (Scheme 1D).9 Each of these methods tolerates some degree of functionalization in the benzene ring of benzophosphole, and they have given access to benzo[b]phospholes substituted at both 2- and 3-positions (Scheme 1). It is noteworthy that these methods are most effective in the preparations of 2,3-diarylbenzophosphole oxides. In turn, the application of radical addition/cyclization of diaryl(arylethynyl)phosphine with alkanes is limited to the formation of a benzophosphole core possessing an alkyl substituent at the 2-positions.10
Scheme 1. Previous Preparations of 2,3-Diarylbenzophoshole Oxides.
Benzophosphole oxides having a single ring substituent have received much less attention4c,4d,11 and, to the best of our knowledge, only two methods for preparing 3-arylbenzophosphole oxides have been reported to date (Scheme 2). First, the Suzuki coupling of 3-bromo-1-phenylbenzophosphole oxide with 2-aminophenylboronic acid was presented in Doosan’s patent (Scheme 2A).12 More recently, 1,3-diphenylbenzophosphole oxide was obtained from phenyl-H-phosphinous acid in a reaction that involves double C-P formation (Scheme 2B).13 Subsequent work by the same group has provided analogues having p-substituted aryl groups in the 3-position, or modified P-phenyl rings (Scheme 2C).13b However, with this methodology, the substitution pattern in the product is constrained by the substituents in the parent alkene or H-phosphinic acid so that the substituent which appears in the p-position of the 3-phenyl substituent will also appear in the 6-position of the benzophosphole skeleton. The development of procedures leading to 3-arylbenzo[b]phosphole oxides from easily available starting materials that diverge at a late stage of the synthesis is therefore desirable. Physicochemical investigations have revealed that substitution at the 3-position has a significant effect on the photoluminescence of quite heavily substituted benzophosphole oxides,14 but the photoluminescence properties of simple 2-H-3-arylbenzophosphole oxides have not yet been presented in the literature. We therefore focus on preparing and analyzing this class here.
Scheme 2. Examples of Preparations of 3-Arylbenzophoshole Oxides.
Results and Discussion
The synthesis of 3-arylbenzophosphole oxides presented here involves a Suzuki–Miyaura protocol that couples aryl boronic acids to a recently described class of benzophosphol-3-yl triflates (Scheme 3).15 In a previous study, where we showed that these reagents have interesting reactivity toward Grignard reagents, we prepared them through the reaction of benzophospholan-3-one oxides 2 with Tf2O in the presence of N,N-diisopropylethylamine (DIPEA) (Scheme 3b). However, when carried out on a larger scale, this reaction proved difficult to control. We have therefore developed a more scalable synthesis of triflates 3 that employs a milder triflating agent, PhN(OTf)2, in the presence of NaH in tetrahydrofuran (THF). Under these conditions, we have successfully obtained triflates 3 from benzophospholan-3-one oxides 2 with good yields on gram scales (Scheme 3c). The structure of 3d was additionally determined by X-ray crystallography (see the Supporting Information (SI), Figure S1a–c, Tables S1–S2).
Scheme 3. Synthesis of Triflates 3.
Having triflates 3 in hand, we optimized conditions for the reaction of triflates 3 with aryl boronic acids. As a model triflate, we have used compound 3a and subjected it to the reaction with phenylboronic acid (4a) (Table 1). The reaction condition was chosen in accordance with the best literature report for Suzuki–Miyaura couplings of vinyl triflates.16
Table 1. Optimization of the Conditions of Reaction of 3a with Phenylboronic Acid (4a)a.
| no. | base | catalyst (mol %)/ligand (mol %) | conditions | yield of 5a (%)b,c |
|---|---|---|---|---|
| 1 | K2CO3 | Pd(PPh3)4 (5) | DMF, 110 °C | 85 (100)d |
| 2 | K2CO3 | Pd(PPh3)4 (5) | THF, 60 °C | 57 (100) |
| 3 | K2CO3 | Pd(PPh3)4 (5) | toluene, 80 °C | 52 (76) |
| 4 | K2CO3 | Pd(PPh3)4 (5) | toluene, 110 °C | 87 (100) |
| 5 | K2CO3 | Pd(PPh3)4 (5) | 1,4-dioxane, rt | 79 (82) |
| 6 | K2CO3 | Pd(PPh3)4 (5) | 1,4-dioxane, 80 °C | 74 (100) |
| 7 | K2CO3 | Pd(PPh3)4 (5) | DME, 50 °C | 55 (88.5) |
| 8 | K2CO3 | Pd(PPh3)4 (5) | DME, 80 °C | 61 (85) |
| 9 | K2CO3 | Pd(PPh3)4 (5) | DME, 110 °C | 88 (100) |
| 10 | Na2CO3(aq.) | Pd(PPh3)4 (5) | DME, 110 °C | 62 (100) |
| 11 | Na2CO3 (aq.) | Pd(PPh3)4 (5) | DME, 110 °C | 60 (100)e |
| 12 | KF | Pd(OAc)2 (2)/PCy3 (2.4) | DME, 85 °C | 21 (46)f |
| 13 | KF | Pd(OAc)2 (2)/PTol3 (2.4) | THF, rt | 17 (33)g |
| 14 | Na2CO3 | PdCl2 (5)/PTol3 (5) | THF, 40 °C | 13 (20)h |
Reaction conditions: 3a (0.1 mmol), 4a (0.12 mmol), base (0.2 mmol), Pd(PPh3)4 (5.0 μmol), solvent (1 mL), temp. (as indicated), 24 h (entries 1–11); 3a (0.267 mmol), 4a (0.32 mmol), base (0.534 mmol), catalyst (as indicated), ligand (as indicated), solvent (1 mL), temp. (as indicated), 24 h (entries 12–14).
Isolated yields.
Numbers in parentheses indicate estimated yields (in reference to the starting material) according to 31P NMR.
Yield according to the 1H NMR spectrum.
3 equiv of LiCl was added to the reaction mixture.
The formation of ketone 2a was observed, but it was not isolated.
Additionally, 24% of ketone 2a was isolated.
Additionally, 13% of ketone 2a was isolated.
In general, the most active catalyst for the reaction of 3a with boronic acid 4a was found to be Pd(PPh3)4 (Table 1, entries 1–11), which is consistent with literature reports of other Suzuki couplings involving vinyl triflates.16 The Pd(PPh3)4 catalyst was compatible with a variety of solvents (THF, 1,2-dimethoxyethane (DME), N,N-dimethylformamide (DMF), 1,4-dioxane, toluene) and each provided the product in moderate to good yields (Table 1, entries 1–10). From the outset, the degree of consumption of the starting material was found to depend strongly on temperature. In reactions conducted below the solvent boiling point: DME (50 and 80 °C), toluene (80 °C), and 1,4-dioxane (rt), significant amounts of unreacted triflate 3a were recovered (Table 1, entries 3, 5, 7–8), and the expected product 5a was isolated in only 52, 79, 55, and 61% yields, respectively. The coupling was found to work best when the reaction was carried out in sealed tubes at 110 °C (for DMF, toluene, and DME); complete conversion of the triflate 3a was then observed, and the desired product 5a was obtained in yields ranging from 85 to 88% (Table 1, entries 1, 4, 9). The highest product purity was obtained when reactions were carried out in DME (Table 1, entry 9); this is because some aromatic coproducts (probably arising from the polymerization of the boronic acid) were observed in toluene and DMF, and these complicated the purification of 5a (Table 1, entries 1, 4). DME was also the best solvent in terms of separating the benzophosphole oxide product 5a from Ph3P(O) (a by-product that arises from catalyst decomposition in yields of up to 15%, depending on the conditions). For the most demanding (i.e., least soluble) compounds, DMF provides a useful option (Table 1, entry 1). Both of the bases used to promote the reaction in DME (solid K2CO3, aq. Na2CO3) gave 5a as the sole product (Table 1, entries 9–10), but a better workup was achieved with K3CO3 rather than Na2CO3 (88 vs 62%, Table 1, entries 9, 10). The addition of LiCl (by analogy with the literature16a) failed to improve the isolated yield (60%, Table 1, entry 11) and also produced significant quantities of Ph3P(O) by-product that complicated the workup. Simultaneously, we verified the efficiency of other catalytic systems. Unfortunately, the assays made with Pd(OAc)217 were both significantly less effective than reactions using Pd(PPh3)4 (Table 1, entries 12–13) and gave similar outcomes in terms of conversion and selectivity (ketone 2a was formed in the reaction mixture). The poorest results came when PdCl2 alone was used as the catalyst (Table 1, entry 13).18 In this case, only 20% conversion was observed, and product 5a was isolated in poor yield (13%).
Given that the results of this preliminary investigation seemed to delineate Pd(PPh3)4/K3CO3 in DME at 110 °C over a 24 h system (Table 1, entry 9) as a system without significant deficiencies, we adopted these conditions for our subsequent studies (Table 2).
Table 2. Scope of the Reaction of 3a with Different Aryl Boronic Acids 4a,b,c.
Reaction conditions: 3a (0.134 mmol), 4 (0.16 mmol), K2CO3 (0.27 mmol), Pd(PPh3)4 (6.7 μmol), DME (1 mL), 110 °C, 24 h.
Isolated yields.
Numbers in parentheses indicate estimated yields (in reference to the starting material) according to 31P NMR.
For fractions that, after purification, were contaminated with up to 5–7% of Ph3P(O), the yields of products were calculated according to 1H NMR.
The promising optimization results prompted us to investigate the reactivity of triflate 3a toward other aryl boronic acids 4b–n. Under the best conditions (Table 1, entry 9), we were able to achieve complete conversions of 3a for a variety of boronic acids with electron-donating substituents (methyl, methoxy, hydroxyl, amino groups) as well as electron-withdrawing groups (halogens—chlorine, fluorine, and nitro group). Overall, the desired benzophosphole oxides 5b–n were obtained selectively with good to excellent yields. In general, the isolated yields of benzophosphole oxides possessing a p-substituted ring (5b, 5e, 5h, and 5j) were very good, in a range of 92–99%, and their separation from Ph3P(O) was easily achieved by column chromatography. In turn, p-chloro derivative 5m and benzophosphole oxides arising from m- and o-substituted phenylboronic acids (4c, 4d, 4f, 4g, 4l) have formed inseparable mixtures with Ph3P(O), which did not allow to calculate isolated yields. The yields of fractions of 5c,d,f,g,l, and 5m after chromatography columns possessing up to 5–7% of Ph3P(O) were calculated according to 1H NMR (58–82%). The exception was the m-(fluorophenyl)benzophosphole 5k, obtained from 4k, which was isolated in 94% yield. The separation of more polar benzophosphole oxides 5h, 5i, and 5n was more successful. For benzophosphole oxides 5h and 5n, which possess unprotected p-hydroxyl and nitro groups, the isolated yield were high (83–92%). Benzophosphole 5i, which features a m-aminophenyl substituent, proved difficult to work up, with some compounds being lost during chromatography, despite the addition of triethylamine to the eluent.
Subsequently, we investigated the influence of the substituent in the benzo ring of benzophosphol-3-yl triflates 3b–d upon the reaction with various boronic acids (Table 3). In general, the reaction appears to be quite tolerant to a range of substitution patterns in the benzophosphole rings, and we observed full conversion in all reactions conducted. Except for 6a, 6b, and 6j, the benzophosphole oxides 6 derived from 3b were isolated in high purity and excellent yields (84–99%). 7a, obtained from 3c, was isolated in only moderate yield (68%) because it was difficult to separate from Ph3P(O). Since our reactions were routinely carried out on a submillimolar scale, we decided to investigate a scaled-up preparation starting from 1 mmol of 3b. It was found that 3b was fully consumed upon reaction with 4n, and 6n was isolated in 91% yield. In turn, benzophosphole oxides 8a, 8b, and 8n derived from 3d revealed difficulties in complete separation from Ph3P(O), and their yields were calculated according to 1H NMR (81–90%). Their more polar analogues 8h and 8i were isolated free of Ph3P(O).
Table 3. Reaction of Other Benzophosph-3-yl Triflates 3b–d with Aryl Boronic Acids 4a,b,c.
Reaction conditions: 3 (0.134 mmol), 4 (0.16 mmol), K2CO3 (0.27 mmol), Pd(PPh3)4 (6.7 μmol), DME (1 mL), 110 °C, 24 h.
Isolated yields.
Numbers in parentheses indicate estimated (in reference to the starting material) yields according to 31P NMR.
For fractions that, after purification, were contaminated with up to 5–7% of Ph3P(O), the yields of products were calculated according to 1H NMR.
Reaction was carried out in a 1 mmol scale starting from 0.389 g of 3b, 4n (1.2 mmol), K2CO3 (2 mmol), Pd(PPh3)4 (0.05 mmol), DME (5 mL), 110 °C, 24 h.
8h was contaminated with 2% of 3d according to 1H NMR.
Most of the benzophosphole oxide products were isolated in the form of waxy solids or oils. Only those possessing hydroxy (5h, 6h, 8h), amino (5i, 6i, 8i), and nitro groups (5n, 6n, 8n) were obtained as solids. Good-quality diffraction patterns were obtained only for compounds 5n and 6n, and these were fully characterized by X-ray studies. Compounds 5n (see the SI, Figure S2) and 6n (see the SI, Figure S3) crystallize in the monoclinic space groups: I2/a (5n) and P21/n (6n) with eight and four molecules in the unit cell, respectively (see the SI, Table S2).
The closest analogues of 3-arylbenzo[b]phosphole oxides 5: 1,2,3-triphenylbenzophosphole oxide (TPPIO, λem = 462 nm, ΦF = 1.2%)19 and other 2,3-disubstituted derivatives14,20 revealed weak fluorescence in diluted THF solutions, while 1,2-diphenylbenzophosphole oxide (λem = 415–417 nm, ΦF = 30–83%)4a,4d,21 is a good fluorophore. To briefly screen the optical properties of benzo[b]phosphole oxides 5 under similar conditions (Figure 1), we have studied several examples showing a variety of substitution patterns in the phenyl ring: unsubstituted 5a, 5e, and 5h bearing electron-donating groups (OMe and OH, respectively) and 5f, 5n possessing electron-withdrawing groups (F, NO2, respectively) (data collected in Table 4). The emission properties of 5j and 5a compounds are characterized by lower fluorescence quantum yields (0.46–0.68%, respectively) and blue-shifted maxima relative to TPPIO. As expected, the hypsochromic effect is less marked relative to 1,2-diphenylbenzophosphole oxide.4a In contrast to 5a, 5n bearing a nitro substituent was not fluorescent in THF solutions. In turn, the presence of electron-donating groups (OMe and OH) in 5e and 5h affected both absorption and emission properties in THF solutions. Two absorption maxima were found in this region at 310 and 330 nm for both compounds.22 The emissive properties of 5e (R2 = OMe, ΦF = 0.73%) and 5h (R2 = OH, ΦF = 1.53%) in THF were improved in comparison to 5a.14b,14c Both compounds 5e and 5h have revealed the absolute fluorescence yields, which were comparable to TPPIO(19) and 1,2-diphenyl-3-(p-methoxyphenyl)benzophosphole oxide14a (ΦF = 1.0%) but still, emission peaks for compounds 5e (λem = 409 nm) and 5h (λem = 445 nm) are blue-shifted compared to TPPIO(19) (λem = 462 nm) and 1,3-diphenyl-2-(p-hydroxyphenyl)benzophosphole oxide14a (λem = 485 nm). The optical properties of 5 can be attributed to reduced conjugation that follows from the absence of an aryl substituent at the 2-position. In turn, low ΦF observed for investigated compounds could be due to the intramolecular rotation or vibration of the 3-aryl groups in a solution like in TPPIO.19
Figure 1.
(a) Normalized absorption spectra of 5a,e,h,j,n compounds in THF solutions. (b) Normalized fluorescence emission spectra of 5a,e,h,j,n compounds in THF solutions. The fluorescence emission spectrum of compound 5n was not normalized due to the lack of emission. For the emission measurements, the excitation wavelength was set at a wavelength corresponding to the absorption maximum of each compound (λabs.). All spectra were recorded for concentration 10–5 M.
Table 4. Optical Data for 5a,e,h,j,n.
| comp. | solvent | λabs [nm] | ε [103 M–1*cm–1] | λem [nm]a | ΦF (%)b | Stokes shift [cm–1] |
|---|---|---|---|---|---|---|
| 5a | toluene | 325 | 2.12 | 405 | 0.17 | 6078 |
| THF | 316 | 3.87 | 410 | n/d,c 0.68d | 7315 | |
| DMSO | 318 | 2.34 | 410 | 0.70 | 7056 | |
| DMF | 318 | 2.68 | 408 | 0.41 | 6937 | |
| ACN | 320 | 2.34 | 414 | 0.20 | 7095 | |
| 5e | toluene | 332 | 3.72 | 407 | 0.18 | 5550 |
| THF | 330 | 2.72 | 409 | 0.73c | 5853 | |
| DMSO | 328 | 3.90 | 425 | 0.60 | 6958 | |
| DMF | 326 | 3.74 | 419 | 0.38 | 6808 | |
| ACN | 326 | 3.37 | 416 | 0.19 | 6636 | |
| 5j | toluene | 324 | 2.22 | 398 | 0.18 | 5739 |
| THF | 316 | 2.59 | 390 | n/d,c 0.46d | 6646 | |
| DMSO | 318 | 2.42 | 410 | 0.67 | 7056 | |
| DMF | 318 | 2.28 | 398 | 0.44 | 6321 | |
| ACN | 322 | 2.10 | 397 | 0.22 | 5867 | |
| 5h | toluene | 325 | 1.40 | 414 | 1.74 | 6615 |
| THF | 330 | 4.19 | 445 | 1.53c | 7831 | |
| DMSO | 334 | 2.90 | 450 | 0.55 | 7718 | |
| DMF | 332 | 3.03 | 450 | 0.29 | 7898 | |
| ACN | 329 | 2.60 | 433 | 0.12 | 7300 | |
| 5n | toluene | 325 | 0.42 | 484 | 0.43 | 10 108 |
| THF | 315 | 1.60 | - | - | - | |
| DMSO | 317 | 2.27 | - | - | - | |
| DMF | 317 | 3.20 | - | - | - | |
| ACN | 317 | 2.59 | - | - | - |
Excitation longest wavelength: λabs.
Fluorescence quantum yields were determined by comparison with a fluorescence standard quinine sulfate dehydrate.
Absolute fluorescence yield was calculated using a calibrating sphere.
For 5a (λabs = 410 nm) and 5j (λabs = 390 nm), faintly fluorescent at 10–5 M, absolute fluorescence yield was calculated using a calibrating sphere at 10–4 M [for both Amax = 0.175, ε = 1.75 × 103 M–1*cm–1] (see the SI, Figure S8).
The optical properties of compounds 5a, 5e, 5j, 5h, and 5n in various solvents are summarized in Table 4 and were used to draw the Lippert–Mataga plots (see the SI, Figure S8). A comparison of the absorption and emission spectra collected for compound 5a is presented in Figure 2 (for spectra collected for compounds 5e, 5j, 5h, and 5n, see the SI, Figures S4–S7). For 5a and other investigated compounds, the absorption bands in different polar solvents do not significantly differ. In turn, in much less polar toluene, most compounds revealed a single red-shifted absorption maximum at 325 nm (and for 5e at 324 nm), probably caused by π-stacking interactions,23 which lower the ground-state energy. The emissive properties of unsubstituted benzophosphole oxide 5a (λem = 405–414 nm) did not exhibit strong solvent dependence in λem values, and the corresponding Lippert–Mataga plot was highly linear (R2 = 0.93). The fluorescence quantum yield of 5a increased from 0.17% (toluene) to the maximal value in DMSO (0.70%) and then gradually lowered from DMF (0.41%) to ACN (0.2%). Regardless of the substitution pattern, benzophosphole oxides 5e and 5j displayed similarities to 5a in λem and ΦF values in the investigated solvents. However, for both (5e and 5j), the corresponding Lippert–Mataga plots display much worst linearity (R2 = 0.72 and R2 = 0.20). The emission peak maxima observed for benzophosphole oxides 5a, 5e, and 5j come from the locally excited (LE) state. First, values of ΦF are improved with solvent polarity, but then the possibility of nonradiative transitions increases, and fluorescence yield decreases (DMF and ACN). However, in DMSO, due to some other specific interactions, the emission spectrum becomes more structured, and the ΦF value reflects these two effects.24
Figure 2.
(a) Normalized absorption spectra of 5a in different solvents at 10–5 M. (b) Normalized fluorescence spectra of 5a in different solvents at 10–5 M. Excitation wavelength: λabs.
The properties of benzophosphole oxide 5h stand out from those described for benzophosphole oxides 5a, 5e, and 5j. Notably, in weakly solvating toluene compound, 5h fluoresces at λem = 414 nm with the highest ΦF value due to reduced possibility of nonradiative dissipation (νabs – νem = 6615 cm–1). The change in polarity from toluene to THF shifts a character of interactions from π–π stacking or O–H···π interactions23 (in toluene) to hydrogen bonds (from THF to ACN) and causes a bathochromic shift of emission bands (433–450 nm) in the latter. Unlike 5a, for 5h, the tendency in the fluorescence yield is gradually decreasing with polarity when the nonradiative transitions become more effective.
In turn, benzophosphole oxide 5n is characterized by the strong Stokes-shifted ICT fluorescence in toluene (νabs – νem = 10 108 cm–1). However, its ΦF is higher than those observed for 5a (Table 4). In more polar solvents (THF, DMSO, DMF, ACN), benzophosphole oxide 5n is not fluorescent mostly due to the quenching properties of the nitro group25 or the preferential nonradiative decay of ICT states.14b,26
It is generally accepted that the photoluminescence properties of benzophosphole oxides27 are principally associated with a π (HOMO) to π* (LUMO) transition within the benzophosphole core.28 Therefore, density functional theory (DFT) calculations at the DFT/B3LYP/6-31+G(d,p) level of theory29 supported the above interpretation of the optical data, with a correlation of the HOMO–LUMO bandgap to the various substituent groups present within our library of 3-arylbenzophosphole oxides (5a–n, see the SI, Figure S10). The comparison of calculated gap energies to reported cases allowed us to divide the investigated analogous 5a–n into two main categories. Compounds (5a–h, 5j–m) revealed lower conjugation levels arising from the absence of the substituent at the 2-position, which is manifested in significantly wider HOMO–LUMO gaps (4.18–4.49 eV) than 1,2,3-triphenylbenzophosphole oxide (TPPIO, 3.95 eV) possessing phenyl rings at both the 2- and 3-positions of the core benzophosphole.19 In this class, in analogy to TPPIO,19 the LUMO electron population density map is determined quite tightly by the benzophosphole ring, but the properties of the 3-aryl substituent express themselves more strongly upon the HOMO (with an effect that is most marked in benzophosphole oxides 5e, 5g, and 5h). The calculations at the TD-DFT/B3LYP/6-31+g-dp level proved that S0 → S1 transitions in 5a and 5j are mainly attributable to π → π* of the benzophosphole ring (see the SI, Table S4). For both compounds (5a and 5j), the absorption band at 331 nm (which refers to 316 nm in solution) in the visible region comes from H → L excitation. In turn, for 5e and 5h, which have displayed two absorption maxima, two transitions with the highest probability and contribution level have been found (see the SI, Table S4 and Figure S13). For the higher energetic band at 305 nm (at 310 nm in solution), H-1 → L transition is responsible. The longest wavelength absorption maximum at 349 nm (at 330 nm in solution) arrives from localized transition H → L. In analogy to the absorption, the emission of benzophosphole oxides 5a, 5e, and 5j originates from LE states. The small changes of dipole moments (μ) between S0 and S1 for compounds 5a, 5e, 5h, and 5j (see the SI, Table S5) indicate that those compounds do not form highly polarizable excited states affected by the solvent polarity, which are responsible for the Stokes-shifted ICT fluorescence. This stays in line with obtained experimental data and the analysis of the corresponding Lippert–Mataga plots.
The analysis above breaks down at the electronic extremes. The calculations revealed that the compounds possessing either amino (5i) or nitro (5n) substituents on the phenyl ring differ significantly from the others (5a–h,j–m) and TPPIO.19 The nitro substituent in compound 5n causes the HOMO–LUMO gap to shrink significantly (3.75 eV), relative to 5a, with both the LUMO and HOMO levels falling well below compound 5a. Conversely, the HOMO–LUMO gaps for 5i possessing an amino functional group equals 3.99 eV. Both these substituents (amino and nitro) also strongly affected the electron distribution within the orbitals, defining their acceptor–donor properties. For 5i, donating the aminophenyl ring is the dominant component of the HOMO, while the accepting benzophosphole ring provides the major contribution to the LUMO. The reverse appears in 5n, where the LUMO is dominated by the nitrophenyl group, and the HOMO is mainly localized on the benzophosphole. Therefore, the benzophosphole ring in 5n behaves as a donor, and the m-NO2-C6H4 unit is an acceptor of charge. These orbital characteristics (high separation of charge and orbitals) imply that H → L has an intramolecular charge transfer (ICT) character. According to time-dependent density functional theory (TD-DFT) calculations for 5n, the difference in μ between the excited state (4.88 D) and its ground-state counterpart (20.94 D) is significant, suggesting that ICT is a major factor in the observed fluorescence properties. However, the absorption band maximum of 5n is determined by other transitions (H → L+1) because of the geometrically small overlap of the HOMO and the LUMO.
Conclusions
In summary, we developed a synthetic route to 3-arylbenzophosphole oxides starting from the readily available benzophosphol-3-yl triflates. The access to benzophosphol-3-yl triflates on a larger scale has been presented. The tolerance of the method for diverse substitution patterns in the structure of boronic acid and the benzophosphole core has been proved. The applicability of the method for larger-scale preparations has been confirmed. Although some complications in the separation of the product from Ph3P(O) have been observed, this method gives access to 3-arylbenzophosphole oxides, which can be used for functionalization at the 2-position. A preliminary investigation of the optical properties of obtained 3-arylbenzophosphole oxides has been conducted. Despite the fluorescence quantum yields of 3-arybenzophosphole oxides remaining poor, these compounds can be used for the rational design of other fluorophores, especially when it comes to exploiting and improving the electron-donor properties of these model compounds. The theoretical studies regarding the HOMO–LUMO gaps, the influence of the substitution pattern, and the differences in the geometry of the ground and excited states of investigated compounds were undertaken. It was found that the electron-donating substituents enhance emissive properties. Further investigation of the reactivity and optical properties of benzophosphole oxides is on the way in our laboratory.
Experimental Section
All reactions were performed under an argon atmosphere using Schlenk techniques. Only dry solvents were used, and glassware was heated under vacuum prior to use. All chemicals were used as received unless noted otherwise. Solvents for chromatography and crystallization were distilled once before use, and the solvents for extraction were used as received. THF and toluene were distilled from sodium/benzophenone ketyl under argon. Dichloromethane (DCM) was dried using P4O10 and distilled before use. 1,4-Dioxane and DME were predistilled and kept over molecular sieves.
1H NMR, 31P{1H} NMR, and 13C{1H} NMR spectra were recorded on a Bruker Advance 500 spectrometer at ambient temperature in CDCl3 unless otherwise noted. Chemical shifts (δ) are reported in ppm from tetramethylsilane with the solvent as an internal indicator (CDCl3 7.27 ppm for 1H and 77 ppm for 13C). Structural assignments were made with additional information from DEPT experiments. Mass spectra were recorded on Shimadzu GC-MS QP2010S in electron ionization (EI). Melting points were determined on Büchi Melting Point M-560 in a capillary tube and were uncorrected. High-performance liquid chromatography-high-resolution mass spectrometry (HPLC-HRMS) was performed on Shimazu HRMS ESI-IT-TOF using reverse-phase stationary phase with water/MeCN 65:35 as an eluent, electrospray ionization (ESI), and the IT-TOF detector. Elementary analyses were performed on PERKIN ELMER CHN 2400. Thin-layer chromatography (TLC) was performed with precoated silica gel plates and visualized by UV light or KMnO4 solution or iodide on silica gel. The reaction mixtures were purified by column chromatography over silica gel (60–240 mesh).
Room temperature UV–vis absorption spectra (in THF) were recorded on a V-660 JASCO spectrophotometer. Photoluminescence measurements (in THF) were carried out with a Photon Technology International Inc. Spectrofluorometer equipped with a continuous wave Xe-arc lamp as a light source. The spectral resolution was maintained at 1 nm. The absolute fluorescence yield (ΦF) (in THF) was determined by using a K-Sphere “Petite” integrating sphere (80 mm diameter) connected to a spectrofluorometer.
UV–vis absorption spectra (in toluene, DCM, ACN, DMF, DMSO) were recorded with a Cary 50 Conc spectrophotometer (Varian, Australia). Steady-state fluorescence spectra were recorded with an FS5 spectrofluorometer (Edinburgh Instruments, U.K.). Fluorescence emission spectra (in toluene, DMSO, DMF, ACN) were recorded with excitation set at a wavelength corresponding to the maximum absorption of each sample. The excitation and emission slits were 2/1.5 nm, respectively. Emission spectra were corrected for the wavelength-dependent efficiency of the excitation source and the detector system. All spectroscopic measurements were performed using 1 cm path-length quartz cuvettes (Hellma, Germany) at room temperature (20 °C).
All samples were centrifuged before experiments (14 000 rpm, 10 min) to eliminate any aggregated form of compound suspended in a solvent. Analysis of the concentration of the samples before and after centrifugation (examination of absorbance value before and after centrifugation) confirmed the existence of only a monomeric form of the compound in the solution.
Fluorescence quantum yields were determined by comparison with a fluorescence standard Quinine sulfate dihydrate (0.5 mol L–1 H2SO4).30 The fluorescence spectra of dilute solutions (A < 0.05) of the compound and the standard were recorded under exactly the same experimental conditions. The quantum yield of the compound (ΦF) was calculated from
 |
where the subscript R refers to the reference solution (standard), IF and IFR are the corrected fluorescence spectra, and n and nR are the refractive indexes of solvents. The integrals represent the area under the fluorescence spectra.31
Single crystals for 3d were obtained by dissolving 30 mg of 3d (an oil solidified upon standing in the fridge) in about 0.7 mL of Et2O and 0.3 mL of hexane in an NMR tube. After 1 h of storage in the fridge, yellowish crystals appeared. The obtained crystals were isolated and dried for 24 h at rt.
Single crystals for 5n were obtained by dissolving 30 mg of 5n (a foam solid from the chromatography column) in about 0.7 mL of AcOEt and 0.3 mL of hexane in an NMR tube. Then, after 48 h of storage in the fridge, colorless crystals appeared. The obtained crystals were isolated and dried for 24 h at rt.
Single crystals for 6n were obtained by dissolving 30 mg of 6n (a solid from the chromatography column) in about 1 mL of AcOEt and 0.1 mL of MeOH in the NMR tube. Then, after a week at rt, colorless crystals appeared. The obtained crystals were isolated and dried for 24 h at rt.
The X-ray intensity data for 3d, 5n, and 6n were measured with an IPDS2T diffractometer equipped with an STOE image plate detector system and microfocus X-ray sources providing Kα radiation by high-grade multilayer X-ray mirror optics for Mo (λ = 0.71073 Å) wavelengths. The measurements were carried out at 120 K. The structures of the compounds were solved by direct methods and refined against F2 with the Shelxs-2008 and Shelxl-2008 programs32 run under WinGX.33 Non-hydrogen atoms were refined with anisotropic displacement parameters. The isotropic displacement parameters of all hydrogens were fixed to 1.2 Ueq for aromatic (1.5 times for methyl) groups.
To calculate the HOMO–LUMO gaps, the quantum-chemical calculations were carried out at the DFT/B3LYP/6-31+G(d,p) level of theory. The ground-state (S0) molecular geometries were fully optimized by restricted closed-shell formalism and without any symmetry restriction. A subsequent vibration analysis was also performed to confirm that the structure of each molecule corresponds at least to a local minimum on its potential energy surface. In the next step, the UV–VIS spectra calculations (vertical excitation energy for the S0 → S1 electronic transitions) were performed for the selected structures with the TD-DFT/B3LYP/6-31+G(d,p) formalism. The GaussSum 3.0 software package34 was employed to deconvolute the computed electronic transitions and to determine the contribution of the main electronic transitions. The results are listed in Table S4. Additionally, on the basis of fully optimized ground-state structure, TD-DFT/ B3LYP/6-31+g-dp calculations have been performed to determine the low-lying excited states (S1) of 5a, 5e, 5h, 5j, and 5n compounds. All calculations were performed by the Gaussian 09 package.35
The starting compounds were prepared according to reported methods: phenyl(methyl)phosphine oxide,36 methyl 2-iodobenzoate,37 methyl 2-iodo-6-methylbenzoate,38 methyl 2-iodo-5-chlorobenzoate,39 2-iodo-4-methoxybenzoic acid,40 methyl 2-iodo-4-methoxybenzoate,41 (2-methoxycarbonylphenyl)(methyl)phenylphosphine oxide (1a),15 [(2-methoxycarbonyl)-6-methylphenyl]methylphenylphosphine oxide (1b),15 [(2-methoxycarbonyl)-5-chlorophenyl]methylphenylphosphine oxide (1c),15 [(2-methoxycarbonyl)-4-methoxyphenyl]methylphenylphosphine oxide (1d),15 1-phenylbenzophospholan-3-one oxide (2a),15,42 1-phenyl-7-methylbenzophospholan-3-one oxide (2b),15 1-phenyl-6-chlorobenzophospholan-3-one oxide (2c),15 and 1-phenyl-5-methoxybenzophospholan-3-one oxide (2d).15
A. Procedure for the Synthesis of Triflates 3 (Scheme 3c)
To a Schlenk tube (100 mL) equipped with a magnetic stirrer and an argon inlet, phosphine oxide 2 (0.58 g, 2.4 mmol) in anhydrous THF (25 mL) was added. The reaction mixture was cooled to −78 °C with a dry ice/acetone bath. Then, NaH (0.105 g, 2.63 mmol, 60% in mineral oil) was added, followed by PhN(OTf)2 (0.944 g, 2.5 mmol). Then, the reaction mixture was allowed to warm to rt for 2 h. The crude reaction mixture was checked using the 31P{1H} NMR technique. After completion of the reaction, the mixture was quenched by the addition of water (5 mL), and THF was evaporated. Then, the residue was extracted with DCM (5 × 10 mL). The collected organic phases were dried over Na2SO4, the solid was filtered off, and the filtrate was evaporated under reduced pressure. The crude product was purified by column chromatography on silica gel using CHCl3/acetone (10:1 v/v) as an eluent.
1-Oxido-1-phenyl-1H-phosphindol-3-yl Trifluoromethanesulfonate (3a)15
2a (0.58 g, 2.4 mmol) was reacted according to general procedure A to afford 3a (74%, 0.665 g, 1.78 mmol). 1H NMR (500 MHz, CDCl3): δ 7.68–7.75 (m, 3H), 7.62–7.66 (m, 1H), 7.56–7.61 (m, 1H), 7.52–7.57 (m, 2H), 7.46–7.50 (m, 2H), 6.31 (d, JH-P = 14.82 Hz, 1H). 13C{1H} NMR (125 MHz, CDCl3): δ 156.7 (d, JC-P = 34.5 Hz, C), 135.8 (d, JC-P = 19.1 Hz, C), 133.4 (d, JC-P = 1.8 Hz, CH), 133.1 (d, JC-P = 2.7 Hz, CH), 132.2 (d, JC-P = 104.5 Hz, C), 131.5 (d, JC-P = 10.9 Hz, CH), 130.8 (d, JC-P = 10.9 Hz, CH), 129.5 (d, JC-P = 8.2 Hz, CH), 129.1 (d, JC-P = 12.7 Hz, CH), 127.5 (d, JC-P = 108.1 Hz, C), 121.0 (d, JC-P = 10.9 Hz, CH), 118.5 (q, JC-P = 321.5 Hz, CF3), 108.9 (d, JC-P = 95.4 Hz, CH). 31P{1H} NMR (202 MHz, CDCl3): δ 32.05 (s).
1-Oxido-1-phenyl-1H-7-methylphosphindol-3-yl Trifluoromethanesulfonate (3b)15
2b (0.077 g, 3 mmol) was reacted according to general procedure A to afford 3b (84%, 0.783 g, 2.01 mmol). 1H NMR (500 MHz, CDCl3): δ 7.73–7.77 (m, 2H), 7.58–7.61 (m, 1H), 7.47–7.53 (m, 3H), 7.35–7.37 (m, 1H), 7.27–7.29 (m, 2H), 6.25 (d, JH-P = 15.13 Hz, 1H), 2.37 (s, 3H). 13C{1H} NMR (125 MHz, CDCl3): δ 156.8 (d, JC-P = 34.5 Hz, C), 142.2 (d, JC-P = 8.2 Hz, C), 135.8 (d, JC-P = 19.1 Hz, C), 133.5 (d, JC-P = 2.7 Hz, CH), 133.1 (d, JC-P = 10.0 Hz, CH), 132.9 (d, JC-P = 2.7 Hz, CH), 130.8 (d, JC-P = 10.9 Hz, CH), 130.3 (d, JC-P = 103.5 Hz, C), 129.2 (d, JC-P = 13.6 Hz, CH), 127.3 (d, JC-P = 106.3 Hz, C), 118.5 (q, JC-P = 321.5 Hz, CF3), 118.48 (d, JC-P = 10.9 Hz, CH), 108.9 (d, JC-P = 95.4 Hz, CH), 19.4 (s, CH3). 31P{1H} NMR (202 MHz, CDCl3): δ 32.43 (s).
1-Oxido-1-phenyl-1H-6-chlorophosphindol-3-yl Trifluoromethanesulfonate (3c)15
2c (0.664 g, 2.4 mmol) was reacted according to general procedure A to afford 3c (60%, 0.589 g, 1.44 mmol). 1H NMR (500 MHz, CDCl3): δ 7.71–7.75 (m, 2H), 7.58–7.65 (m, 3H), 7.45–7.52 (m, 3H), 6.31 (d, JH-P = 15.29 Hz, 1H). 13C{1H} NMR (125 MHz, CDCl3): δ 156.2 (d, JC-P = 33.6 Hz, C), 138.4 (d, JC-P = 14.3 Hz, C), 134.6 (d, JC-P = 100.8 Hz, C), 133.9 (d, JC-P = 19.1 Hz, C), 133.4 (d, JC-P = 2.7 Hz, CH), 133.3 (d, JC-P = 1.8 Hz, CH), 130.8 (d, JC-P = 10.9 Hz, 2CH), 128.9 (d, JC-P = 10.0 Hz, 2CH), 128.4 (d, JC-P = 13.6 Hz, CH), 126.7 (d, JC-P = 108.9 Hz, C), 122.2 (d, JC-P = 11.8 Hz, CH), 118.5 (q, JC-P = 320.6 Hz, CF3), 109.9 (d, JC-P = 98.6 Hz, CH). 31P{1H} NMR (202 MHz, CDCl3): δ 31.17 (s).
1-Oxido-1-phenyl-1H-5-methoxyphosphindol-3-yl Trifluoromethanesulfonate (3d)15
2d (0.653 g, 2.4 mmol) was reacted according to general procedure A to afford 3d (83%, 0.805 g, 1.99 mmol). 1H NMR (500 MHz, CDCl3): δ 7.68–7.72 (m, 2H), 7.57–7.62 (m, 2H), 7.46–7.48 (m, 2H), 7.04–7.05 (m, 1H), 6.97–7.00 (m, 1H), 6.31 (d, JH-P = 14.66 Hz, 1H), 3.91 (s, 3H). 13C{1H} NMR (125 MHz, CDCl3): δ 164.0 (JP-C = 1.8 Hz, C), 155.9 (d, JP-C = 33.6 Hz, C), 138.2 (d, JP-C = 20.9 Hz, C), 132.9 (d, JP-C = 2.7 Hz, CH), 131.1 (d, JP-C = 10.0 Hz, CH), 130.8 (d, JP-C = 11.8 Hz, CH), 129.1 (d, JP-C = 13.6 Hz, CH), 129.7 (d, JP-C = 108.9 Hz, C), 122.7 (d, JP-C = 110.8 Hz, C), 118.6 (q, JP-C = 320.6 Hz, CF3), 115.5 (d, JP-C = 12.7 Hz, CH), 110.5 (d, JP-C = 94.5 Hz, CH), 108.0 (d, JP-C = 11.8 Hz, CH), 55.8 (s, CH3). 31P{1H} NMR (202 MHz, CDCl3): δ 30.90 (s).
B: General Procedure for the Reaction of 3 with Aryl Boronic Acids (Suzuki Coupling) (Tables 2 and 3)
To a reaction vial (5 mL) equipped with a magnetic stirrer and an argon inlet, 3 (0.134 mmol), aryl boronic acid 4 (0.16 mmol), K2CO3 (0.037 g, 0.27 mmol), and Pd(PPh3)4 (7.7 mg, 0.0067 mmol) were added followed by DME (1 mL). The vial was closed using an aluminum cap and heated at 110 °C using heating transfer blocks for 24 h. After that time, the reaction mixture was cooled to rt, and the solvent was evaporated. To the residue, a saturated solution of NaHCO3 (5 mL) or NH4Cl (5 mL, for 5h, 6h, and 8h) and DCM (10 mL) was added, and the mixture was transferred to an extraction funnel. The mixture was extracted with DCM (3 × 10 mL), and the collected organic phases were dried over Na2SO4. The solid was filtered off, and the filtrate evaporated under reduced pressure. The crude reaction mixture was checked using the NMR technique. The crude product was purified by column chromatography on silica gel using CHCl3/MTBE (30:1 v/v) as an eluent.
1,3-Diphenylbenzophosphole Oxide (5a)13
3a (0.05 g, 0.134 mmol) was reacted with PhB(OH)2 (0.0195 g, 0.16 mmol) according to general procedure B to afford 5a as a yellowish oil (88%, 0.0355 g, 0.117 mmol). Rf = 0.28 (30:1 CHCl3/MTBE). 1H NMR (500 MHz, CDCl3): δ 7.77–7.82 (m, 2H), 7.68–7.72 (m, 1H), 7.54–7.57 (m, 2H), 7.51–7.54 (m, 1H), 7.46–7.51 (m, 4H), 7.43–7.48 (m, 3H), 7.40–7.43 (m, 1H), 6.37 (d, JH-P = 23.96 Hz, 1H). 31P{1H} NMR (202 MHz, CDCl3): δ 37.13 (s); 13C{1H} NMR (125 MHz, CDCl3): δ 158.0 (d, JC-P = 15.4 Hz, C), 142.1 (d, JC-P = 27.3 Hz, C), 134.9 (d, JC-P = 16.4 Hz, C), 134.8 (d, JC-P = 105.4 Hz, 2C), 132.6 (d, JC-P = 1.8 Hz, CH), 132.3 (d, JC-P = 2.7 Hz, CH), 130.9 (d, JC-P = 10.9 Hz, 2CH), 129.5 (d, JC-P = 10.0 Hz, CH), 129.4 (d, JC-P = 103.5 Hz, C), 129.3 (d, JC-P = 10.0 Hz, CH), 128.1 (d, JC-P = 11.8 Hz, CH), 127.8 (s, 2CH), 124.0 (d, JC-P = 10.9 Hz, CH), 122.8 (d, JC-P = 99.9 Hz, CH). GC-MS (EI) m/z: 303 (21), 302 (100) (M)+, 301 (91). HRMS (ESI/Q-TOF) m/z: calcd for C20H15OP [M + Na]+, 325.0753, found: 325.0752.
1-Phenyl-3-p-tolylbenzophosphole Oxide (5b)
3a (0.05 g, 0.134 mmol) was reacted with p-TolB(OH)2 (0.0218 g, 0.16 mmol) according to general procedure B to afford 5b as a yellowish oil (96%, 0.0406 g, 0.128 mmol). Rf = 0.29 (30:1 CHCl3/MTBE). 1H NMR (500 MHz, CDCl3): δ 7.77–7.81 (m, 2H), 7.67–7.71 (m, 1H), 7.52–7.55 (m, 1H), 7.49–7.50 (m, 2H), 7.43–7.47 (m, 4H), 7.37–7.43 (m, 1H), 7.30–7.32 (m, 2H), 6.34 (d, JH-P = 24.28 Hz, 1H), 2.44 (s, 3H); 31P{1H} NMR (202 MHz, CDCl3): δ 37.12 (s); 13C{1H} NMR (125 MHz, CDCl3): δ 158.1 (d, JC-P = 15.4 Hz, C), 142.1 (d, JC-P = 28.2 Hz, C), 139.8 (s, C), 134.8 (d, JC-P = 105.4 Hz, C), 132.5 (d, JC-P = 1.8 Hz, CH), 132.2 (d, JC-P = 2.7 Hz, CH), 132.0 (d, JC-P = 16.4 Hz, C), 130.9 (d, JC-P = 10.9 Hz, CH), 129.6 (d, JC-P = 102.6 Hz, C), 129.5 (s, 2CH), 129.4 (d, JC-P = 10.0 Hz, CH), 129.2 (d, JC-P = 10.0 Hz, CH), 128.8 (d, JC-P = 12.7 Hz, CH), 127.7 (s, 2CH), 124.0 (d, JC-P = 11.8 Hz, CH), 122.2 (d, JC-P = 99.9 Hz, CH), 21.4 (s, CH3). GC-MS (EI) m/z: 317 (21), 316 (100) (M)+, 315 (84), 301 (12), 300 (31), 299 (13), 297 (12), 269 (23), 268 (22), 254 (18), 253 (26), 252 (24), 239 (24), 223 (19), 196 (14), 191 (13), 189 (14), 178 (13), 165 (16), 77 (10). HRMS (ESI/Q-TOF) m/z: calcd for C21H17OP [M + H]+, 317.1090 found: 317.1095.
1-Phenyl-3-m-tolylbenzophosphole Oxide (5c)
3a (0.05 g, 0.134 mmol) was reacted with m-TolB(OH)2 (0.0218 g, 0.16 mmol) according to general procedure B to afford 5c (74% according to the 1H NMR spectrum, 0.0367 g) as a mixture with 7% of Ph3P(O). Rf = 0.3 (30:1 CHCl3/MTBE). 1H NMR (500 MHz, CDCl3): δ 7.77–7.81 (m, 2H), 7.67–7.71 (m, 1H), 7.52–7.55 (m, 1H), 7.44–7.50 (m, 4H), 7.40–7.44 (m, 1H), 7.34–7.39 (m, 3H), 7.29–7.31 (m, 1H), 6.36 (d, JH-P = 24.28 Hz, 1H), 2.44 (s, 3H); 31P{1H} NMR (202 MHz, CDCl3): δ 37.17 (s); 13C{1H} NMR (125 MHz, CDCl3): δ 158.2 (d, JC-P = 15.4 Hz, C), 142.1 (d, JC-P = 28.2 Hz, C), 138.6 (s, C), 134.9 (d, JC-P = 16.4 Hz, C), 133.8 (d, JC-P = 105.4 Hz, C), 132.6 (d, JC-P = 1.8 Hz, CH), 132.2 (d, JC-P = 3.4 Hz, CH), 130.9 (d, JC-P = 10.9 Hz, 2CH), 130.3 (s, CH), 129.46 (d, JC-P = 103.5 Hz, C), 129.45 (d, JC-P = 10.9 Hz, CH), 129.2 (d, JC-P = 9.1 Hz, CH), 128.8 (d, JC-P = 12.7 Hz, CH), 128.6 (s, CH), 128.4 (d, JC-P = 1.2 Hz, CH), 124.9 (s, CH), 124.1 (d, JC-P = 10.8 Hz, CH), 122.5 (d, JC-P = 99.9 Hz, CH), 21.5 (s, CH3). GC-MS (EI) m/z: 317 (21), 316 (100) (M)+, 315 (76), 301 (18), 300 (46), 299 (19), 297 (13), 283 (10), 269 (25), 268 (23), 254 (21), 253 (27), 252 (27), 239 (21), 223 (18), 196 (14), 191 (14), 189 (16), 178 (14), 165 (19), 77 (11). HRMS (ESI/Q-TOF) m/z: calcd for C21H17OPNa [M + Na]+, 339.0909, found: 339.0907.
1-Phenyl-3-o-tolylbenzophosphole Oxide (5d)
3a (0.05 g, 0.134 mmol) was reacted with o-TolB(OH)2 (0.0218 g, 0.16 mmol) according to general procedure B to afford 5d as a yellowish oil (87%, 0.0367 g, 0.116 mmol). Rf = 0.27 (30:1 CHCl3/MTBE). 1H NMR (500 MHz, CDCl3): δ 7.80–7.84 (m, 2H), 7.68–7.72 (m, 1H), 7.55–7.58 (m, 1H), 7.43–7.49 (m, 3H), 7.29–7.41 (m, 5H), 7.00–7.02 (m, 1H), 6.31 (d, JH-P = 25.22 Hz, 1H), 2.29 (s, 3H); 31P{1H} NMR (202 MHz, CDCl3): δ 38.16 (s); 13C{1H} NMR (125 MHz, CDCl3): δ 158.3 (d, JC-P = 14.5 Hz, C), 142.9 (d, JC-P = 21.8 Hz, C), 134.8 (d, JC-P = 18.7 Hz, C), 132.8 (d, JC-P = 1.8 Hz, CH), 132.7 (d, JC-P = 104.1 Hz, C), 132.3 (d, JC-P = 2.7 Hz, CH), 130.9 (d, JC-P = 10.9 Hz, CH), 129.5 (d, JC-P = 10.0 Hz, CH), 128.9 (d, JC-P = 10.0 Hz, CH), 128.89 (s, CH), 128.88 (d, JC-P = 12.7 Hz, CH), 124.0 (d, JC-P = 10.9 Hz, CH), 123.6 (d, JC-P = 98.1 Hz, CH), 20.6 (s, CH3). GC-MS (EI) m/z: 317 (22), 316 (100) (M)+, 315 (69), 301 (17), 300 (46), 299 (22), 267 (11), 265 (11), 253 (15), 252 (17), 239 (14), 221 (29), 220 (32), 193 (17), 192 (94), 191 (53), 190 (12), 189 (27), 179 (22), 165 (22), 115 (11), 91 (10), 77 (14). HRMS (ESI/Q-TOF) m/z: calcd for C21H17OP [2M + Na]+, 655.1926; found: 655.1918.
3-p-Anisyl-1-phenylbenzophosphole Oxide (5e)
3a (0.05 g, 0.134 mmol) was reacted with p-AnB(OH)2 (0.0243 g, 0.16 mmol) according to general procedure B to afford 5e as a yellowish oil (99%, 0.0436 g, 0.131 mmol). Rf = 0.26 (30:1 CHCl3/MTBE). 1H NMR (500 MHz, CDCl3): δ 7.76–7.80 (m, 2H), 7.65–7.70 (m, 1H), 7.48–7.55 (m, 5H), 7.37–7.47 (m, 3H), 7.00–7.03 (m, 2H), 6.30 (d, JH-P = 24.12 Hz, 1H), 3.87 (s, 3H); 31P{1H} NMR (202 MHz, CDCl3): δ 36.87 (s); 13C{1H} NMR (125 MHz, CDCl3): δ 160.2 (s, C), 157.7 (d, JC-P = 15.4 Hz, C), 142.2 (d, JC-P = 27.3 Hz, C), 134.0 (d, JC-P = 105.4 Hz, C), 132.5 (d, JC-P = 1.8 Hz, CH), 132.2 (d, JC-P = 2.7 Hz, CH), 132.0 (d, JC-P = 10.0 Hz, CH), 130.9 (d, JC-P = 10.9 Hz, 2CH), 129.6 (d, JC-P = 103.5 Hz, C), 129.4 (d, JC-P = 10.9 Hz, CH), 129.3 (s, 2CH), 129.2 (d, JC-P = 10.0 Hz, CH), 128.8 (d, JC-P = 10.0 Hz, 2CH), 127.2 (d, JC-P = 16.3 Hz, C), 124.8 (d, JC-P = 11.7 Hz, CH), 121.4 (d, JC-P = 100.8 Hz, CH), 114.1 (s, 2CH), 55.4 (s, CH3). GC-MS (EI) m/z: 333 (21), 332 (92) (M)+, 331 (24), 316 (100), 315 (22), 301 (15), 285 (21), 270 (15), 241 (12), 240 (17), 239 (41), 183 (14), 152 (20), 138 (10). HRMS (ESI/Q-TOF) m/z: calcd for C21H17O2PNa [M + Na]+: 355.0858, found: 355.0848.
1-Phenyl-3-(m-anisyl)benzophosphole Oxide (5f)
3a (0.05 g, 0.134 mmol) was reacted with m-AnB(OH)2 (0.0243 g, 0.16 mmol) according to general procedure B to afford 5f (69% according to the 1H NMR spectrum, 0.0315 g) as a mixture with 3% of Ph3P(O). Rf = 0.30 (30:1 CHCl3/MTBE). 1H NMR (500 MHz, CDCl3): δ 7.77–7.81 (m, 2H), 7.69–7.72 (m, 1H), 7.40–7.54 (m, 7H), 7.02–7.14 (m, 3H), 6.38 (d, JH-P = 23.96 Hz, 1H), 3.86 (s, 3H); 31P{1H} NMR (202 MHz, CDCl3): δ 37.07 (s); 13C{1H} NMR (125 MHz, CDCl3): δ 159.8 (s, C), 157.9 (d, JC-P = 15.4 Hz, C), 141.9 (d, JC-P = 27.3 Hz, C), 136.3 (d, JC-P = 16.4 Hz, C), 133.8 (d, JC-P = 105.4 Hz, C), 132.6 (d, JC-P = 1.8 Hz, CH), 132.2 (d, JC-P = 3.6 Hz, CH), 130.9 (d, JC-P = 10.9 Hz, 2CH), 129.9 (s, 2CH), 129.5 (d, JC-P = 10.9 Hz, CH), 129.2 (d, JC-P = 10.0 Hz, CH), 128.8 (d, JC-P = 12.7 Hz, 2CH), 128.5 (d, JC-P = 11.8, CH), 124.0 (d, JC-P = 10.9 Hz, CH), 122.8 (d, JC-P = 99.9 Hz, CH), 120.1 (s, CH), 114.9 (s, CH), 113.4 (s, CH), 55.4 (s, CH3). GC-MS (EI) m/z: 333 (25), 332 (100) (M)+, 331 (72), 317 (29), 316 (95), 315 (29), 301 (16), 285 (35), 284 (30), 283 (11), 271 (13), 270 (30), 269 (12), 255 (19), 253 (18), 252 (24), 241 (15), 240 (15), 239 (43), 226 (10), 223 (12), 195 (12), 194 (12), 183 (19), 165 (39), 152 (23), 126 (11), 77 (18). HRMS (ESI/Q-TOF) m/z: calcd for C42H34O4P2 [2M + Na]+, 687.1825; found: 687.1814.
1-Phenyl-3-(o-anisyl)benzophosphole Oxide (5g)
3a (0.05 g, 0.134 mmol) was reacted with o-AnB(OH)2 (0.0243 g, 0.16 mmol) according to general procedure B to afford 5g (58% according to the 1H NMR spectrum, 0.0275 g) as a mixture with 5% of Ph3P(O). Rf = 0.3 (30:1 CHCl3/MTBE). 1H NMR (500 MHz, CDCl3): δ 7.83–7.88 (m, 2H), 7.63–7.67 (m, 1H), 7.52–7.53 (m, 1H), 7.42–7.47 (m, 4H), 7.33–7.36 (m, 2H), 7.03–7.11 (m, 3H), 6.35 (d, JH-P = 24.91 Hz, 1H), 3.80 (s, 3H); 31P{1H} NMR (202 MHz, CDCl3): δ 37.53 (s); 13C{1H} NMR (125 MHz, CDCl3): δ 156.7 (s, C), 157.9 (d, JC-P = 15.4 Hz, C), 133.0 (d, JC-P = 106.3 Hz, C), 132.4 (d, JC-P = 1.8 Hz, CH), 132.1 (d, JC-P = 2.7 Hz, CH), 131.0 (d, JC-P = 10.9 Hz, 2CH), 130.5 (s, CH), 129.8 (d, JC-P = 1.8 Hz, CH), 129.7 (d, JC-P = 102.8 Hz, C), 129.0 (d, JC-P = 10.9 Hz, CH), 128.7 (d, JC-P = 12.7 Hz, 2CH), 128.5 (d, JC-P = 10.0 Hz, CH), 124.7 (d, JC-P = 11.8 Hz, CH), 123.9 (d, JC-P = 98.1 Hz, CH), 120.8 (s, CH), 111.1 (s, CH), 55.4 (s, CH3). GC-MS (EI) m/z: 333 (23), 332 (100), 331 (67), 317 (44), 316 (59), 315 (35), 301 (14), 299 (17), 270 (17), 255 (11), 254 (12), 253 (26), 252 (28), 241 (11), 240 (11), 239 (40), 236 (11), 223 (28), 194 (15), 183 (17), 179 (14), 178 (23), 165 (50), 152 (18), 126 (13), 107 (10), 77 (20). HRMS (ESI/Q-TOF) m/z: calcd for C21H17O2P [M + Na]+, 355.0858; found: 355.0852.
3-(4-Hydroxyphenyl)-1-phenylbenzophosphole Oxide (5h)
3a (0.05 g, 0.134 mmol) was reacted with p-OH-C6H4B(OH)2 (0.0221 g, 0.16 mmol) according to general procedure B to afford 5h (92%, 0.0392 g, 0.123 mmol) as pale yellow solid, mp = 256.5–257.5 °C. Rf = 0.34 (30:5:1 CHCl3/AcOEt/MeOH). 1H NMR (500 MHz, CDCl3): δ 9.26 (bs, 1H), 7.76–7.80 (m, 2H), 7.66–7.70 (m, 1H), 7.48–7.55 (m, 3H), 7.38–7.43 (m, 2H), 7.37–7.47 (m, 1H), 7.34–7.37 (m, 2H), 7.00–7.03 (m, 2H), 6.23 (d, JH-P = 24.43 Hz, 1H); 31P{1H} NMR (202 MHz, CDCl3): δ 38.71 (s); 13C{1H} NMR (125 MHz, CDCl3): δ 159.9 (s, C). 159.8 (d, JC-P = 16.4 Hz, C), 142.2 (d, JC-P = 28.2 Hz, C), 133.5 (d, JC-P = 106.3 Hz, C), 132.7 (d, JC-P = 1.8 Hz, CH), 132.5 (d, JC-P = 2.7 Hz, CH), 131.0 (d, JC-P = 10.9 Hz, 2CH), 129.5 (d, JC-P = 12.7 Hz, CH), 129.3 (s, 2CH), 129.2 (d, JC-P = 9.1 Hz, CH), 128.9 (d, JC-P = 12.7 Hz, 2CH), 125.8 (d, JC-P = 17.3 Hz, C), 124.4 (d, JC-P = 12.7 Hz, CH), 119.6 (d, JC-P = 101.7 Hz, CH), 116.1 (s, 2CH). HRMS (ESI/Q-TOF) m/z: calcd for C20H16O2P [M + H]+, 319.0888, found: 319.0889.
3-(3-Aminophenyl)-1-phenylbenzophosphole Oxide (5i)
3a (0.05 g, 0.134 mmol) was reacted with m-H2N-C6H4B(OH)2-H2O (0.0248 g, 0.16 mmol) according to general procedure B to afford 5i (67%, 0.0284 g, 0.0875 mmol) as a pale yellow solid, mp = 223.6–224.6 °C. Rf = 0.32 (30:5:1 CHCl3/AcOEt/MeOH). 1H NMR (500 MHz, CDCl3): δ 7.75–7.80 (m, 2H), 7.65–7.69 (m, 1H), 7.48–7.55 (m, 3H), 7.42–7.47 (m, 2H), 7.37–7.41 (m, 1H), 7.25–7.27 (m, 1H), 6.91–6.92 (m, 1H), 6.83 (bs, 1H), 6.78–6.80 (m, 1H), 6.33 (d, JH-P = 24.28 Hz, 1H), 3.86 (m, 2H). 31P{1H} NMR (202 MHz, CDCl3): δ 37.04 (s); 13C{1H} NMR (125 MHz, CDCl3): δ 158.3 (d, JC-P = 15.4 Hz, C), 146.8 (s, C), 142.1 (d, JC-P = 27.3 Hz, C), 136.0 (d, JC-P = 15.4 Hz, C), 133.9 (d, JC-P = 104.5 Hz, 2C), 132.5 (d, JC-P = 1.8 Hz, CH), 132.2 (d, JC-P = 2.7 Hz, CH), 130.9 (d, JC-P = 10.9 Hz, 2CH), 129.7 (s, CH), 129.65 (d, JC-P = 102.6 Hz, C), 129.5 (d, JC-P = 10.0 Hz, CH), 129.2 (d, JC-P = 10.0 Hz, CH), 128.8 (d, JC-P = 12.7 Hz, 2CH), 124.0 (d, JC-P = 10.9 Hz, CH), 122.3 (d, JC-P = 99.9 Hz, CH), 117.9 (s, CH), 116.1 (s, CH), 114.0 (s, CH). HRMS (ESI/Q-TOF) m/z: calcd for C20H17ONP [M + H]+, 318.1048, found: 318.1049.
3-(p-Fluorophenyl)-1-phenylbenzophosphole Oxide (5j)
3a (0.05 g, 0.134 mmol) was reacted with p-F-C6H4B(OH)2 (0.0223 g, 0.16 mmol) according to general procedure B to afford 5j as an orange oil (94%, 0.0403 g, 0.126 mmol). Rf = 0.26 (30:1 CHCl3/MTBE). 1H NMR (500 MHz, CDCl3): δ 7.76–7.80 (m, 2H), 7.67–7.72 (m, 1H), 7.53–7.56 (m, 2H), 7.50–7.51 (m, 1H), 7.40–7.47 (m, 5H), 7.18–7.21 (m, 2H), 6.35 (d, JH-P = 23.80 Hz, 1H). 31P{1H} NMR (202 MHz, CDCl3): δ 36.81 (s); 13C{1H} NMR (125 MHz, CDCl3): δ 163.4 (d, JC-F = 249.8 Hz, C-F), 156.9 (d, JC-P = 15.4 Hz, C), 141.8 (d, JC-P = 27.3 Hz, C), 133.7 (d, JC-P = 105.4 Hz, 2C), 132.6 (d, JC-P = 1.8 Hz, CH), 132.3 (d, JC-P = 3.6 Hz, CH), 132.0 (d, JC-P = 10.0 Hz, 2CH), 130.95 (dd, JC-F = 3.6 Hz, JC-P = 17.3 Hz, C), 130.9 (d, JC-P = 10.9 Hz, 2CH), 129.7 (d, JC-P = 8.7 Hz, CH), 129.5 (dd, JC-F = 32.7 Hz, JC-P = 9.1 Hz, CH), 128.8 (d, JC-P = 12.7 Hz, CH), 128.5 (d, JC-P = 11.8 Hz, CH), 123.9 (d, JC-P = 11.9 Hz, CH), 123.1 (d, JC-P = 99.0 Hz, CH), 115.9 (d, JC-F = 21.8 Hz, CH). GC-MS (EI) m/z: 321 (22), 320 (100) (M)+, 319 (83), 304 (38), 302 (17), 300 (18), 281 (17), 273 (32), 272 (36), 271 (35), 270 (29), 253 (24), 243 (22), 227 (21), 225 (15), 207 (40), 196 (26), 194 (14), 183 (25), 170 (10), 165 (15), 107 (11), 77 (13). HRMS (ESI/Q-TOF) m/z: calcd for C20H15OFP [M + H]+, 321.0845, found: 321.0846.
1-Phenyl-3-(m-fluorophenyl)benzophosphole Oxide (5k)
3a (0.05 g, 0.134 mmol) was reacted with m-F-C6H4B(OH)2 (0.0223 g, 0.16 mmol) according to general procedure B to afford 5k as a yellowish oil (94%, 0.0402 g, 0.125 mmol). Rf = 0.3 (30:1 CHCl3/MTBE). 1H NMR (500 MHz, CDCl3): δ 7.75–7.80 (m, 2H), 7.70–7.72 (m, 1H), 7.51–7.57 (m, 2H), 7.43–7.47 (m, 5H), 7.33–7.35 (m, 1H), 7.24–7.25 (m, 1H), 7.17–7.20 (m, 1H), 6.40 (d, JH-P = 23.64 Hz, 1H). 31P{1H} NMR (202 MHz, CDCl3): δ 36.86 (s); 13C{1H} NMR (125 MHz, CDCl3): δ 162.7 (d, JC-F = 247.9 Hz, C-F), 156.6 (d, JC-P = 16.4 Hz, JC-F = 2.7 Hz, C), 141.6 (d, JC-P = 26.4 Hz, C), 136.9 (d, JC-P = 7.26 Hz, JC-F = 16.35 Hz, C), 133.6 (d, JC-P = 105.4 Hz, C), 132.7 (d, JC-P = 1.8 Hz, CH), 132.4 (d, JC-P = 2.7 Hz, CH), 131.9 (d, JC-P = 10.9 Hz, 2CH), 130.6 (d, JC-P = 10.9 Hz, CH), 129.7 (d, JC-F = 9.1 Hz, CH), 129.4 (d, JC-F = 9.1 Hz, CH), 129.1 (d, JC-P = 103.5 Hz, C), 123.83 (d, JC-P = 11.8 Hz, CH), 123.74 (d, JC-P = 99.0 Hz, CH), 123.6 (d, JC-P = 2.7 Hz, CH), 116.5 (d, JC-F = 21.8 Hz, CH), 114.9 (d, JC-F = 22.7 Hz, CH). GC-MS (EI) m/z: 321 (5), 320 (21) (M)+, 319 (14), 304 (13), 303 (6), 283 (10), 282 (12), 291 (38), 253 (22), 209 (15), 208 (21), 207 (100), 191 (14), 135 (10), 133 (15), 96 (12), 73 (30). HRMS (ESI/Q-TOF) m/z: calcd for C40H28F2O2P2 [2M + Na]+, 663.1425; found: 663.1440.
1-Phenyl-3-(o-fluorophenyl)benzophosphole Oxide (5l)
3a (0.05 g, 0.134 mmol) was reacted with o-F-C6H4B(OH)2 (0.0223 g, 0.16 mmol) according to general procedure B to afford 5l (67% according to the 1H NMR spectrum, 0.0308 g) as a mixture with 5% of Ph3P(O). Rf = 0.26 (30:1 CHCl3/MTBE). 1H NMR (500 MHz, CDCl3): δ 7.79–7.84 (m, 2H), 7.67–7.71 (m, 1H), 7.54–7.57 (m, 1H), 7.44–7.50 (m, 5H), 7.40–7.44 (m, 1H), 7.20–7.30 (m, 3H), 6.45 (d, JH-P = 23.96 Hz, 1H). 31P{1H} NMR (202 MHz, CDCl3): δ 37.26 (s); 13C{1H} NMR (125 MHz, CDCl3): δ 159.4 (d, JC-F = 247.8 Hz, C-F), 152.5 (d, JC-P = 16.4 Hz, C), 141.9 (d, JC-P = 27.3 Hz, C), 132.9 (d, JC-P = 105.4 Hz, C), 132.8 (d, JC-P = 1.8 Hz, CH), 132.3 (d, JC-P = 2.7 Hz, CH), 131.2 (d, JC-P = 8.7 Hz, CH), 131.0 (d, JC-P = 10.9 Hz, 2CH), 130.2 (d, JC-P = 1.8 Hz, CH), 129.6 (d, JC-P = 10.9 Hz, CH), 129.2 (d, JC-P = 102.6 Hz, CH), 128.9 (d, JC-P = 10.3 Hz, CH), 128.89 (d, JC-P = 10.3 Hz, CH), 129.7 (d, JC-P = 12.7 Hz, 2CH), 125.6 (d, JC-P = 98.1 Hz, CH), 124.6 (d, JC-P = 3.6 Hz, CH), 124.0 (d, JC-P = 1.82 Hz, JC-F = 10.9 Hz, CH), 122.8 (dd, JC-P = 16.4 Hz, JC-F = 16.4 Hz, CH), 116.9 (d, JC-F = 21.8 Hz, CH), GC-MS (EI) m/z: 321 (22), 320 (100) (M)+, 319 (66), 304 (25), 303 (10), 301 (10), 273 (28), 272 (21), 271 (19), 270 (18), 254 (18), 253 (46), 252 (38), 243 (20), 227 (20), 207 (24), 194 (12), 186 (18), 165 (12), 151 (10), 77 (12). HRMS (ESI/Q-TOF) m/z: calcd for C20H14FOP [M + Na]+, 343.0659; found: 343.0654.
1-Phenyl-3-(p-chlorophenyl)benzophosphole Oxide (5m)
3a (0.05 g, 0.134 mmol) was reacted with p-Cl-C6H4B(OH)2 (0.025 g, 0.16 mmol) according to general procedure B to afford 5m as a yellowish oil (82% according to the 1H NMR spectrum, 0.0414 g) as a mixture with 7% of Ph3P(O). Rf = 0.32 (30:1 CHCl3/MTBE). 1H NMR (500 MHz, CDCl3): δ 7.75–7.79 (m, 2H), 7.68–7.70 (m, 1H), 7.41–7.55 (m, 10H), 6.38 (d, JH-P = 23.64 Hz, 1H); 31P{1H} NMR (202 MHz, CDCl3): δ 36.83 (s); 13C{1H} NMR (125 MHz, CDCl3): δ 156.7 (d, JC-P = 15.4 Hz, C), 141.7 (d, JC-P = 27.3 Hz, C), 135.6 (s, C), 133.7 (d, JC-P = 105.4 Hz, C), 133.3 (d, JC-P = 17.3 Hz, C), 132.7 (d, JC-P = 1.8 Hz, CH), 132.4 (d, JC-P = 2.7 Hz, CH), 130.9 (d, JC-P = 10.9 Hz, 2CH), 129.7 (d, JC-P = 10.9 Hz, CH), 129.4 (d, JC-P = 10.0 Hz, CH), 129.3 (d, JC-P = 103.5 Hz, C), 129.1 (d, JC-P = 7.2 Hz, 2CH), 128.9 (d, JC-P = 12.7 Hz, CH), 123.8 (d, JC-P = 11.8 Hz, CH), 123.5 (d, JC-P = 99.0 Hz, CH). GC-MS (EI) m/z: 339 (8), 338 (35), 337 (48), 336 (100) (M)+, 335 (88), 332 (11), 321 (11), 320 (34), 319 (14), 289 (18), 288 (21), 285 (10), 283 (24), 281 (26), 259 (21), 255 (11), 254 (49), 253 (62), 252 (10), 243 (19), 212 (14), 209 (16), 208 (18), 207 (79), 196 (23), 194 (12), 178 (10), 177 (16), 176 (31), 165 (21), 152 (10), 151 (14), 150 (11), 139 (11), 126 (14), 107 (12), 77 (19). HRMS (ESI/Q-TOF) m/z: calcd for C20H14ClOPNa [M + Na]+, 359.0363; found: 359.0358.
3-(m-Nitrophenyl)-1-phenylbenzophosphole Oxide (5n)
3a (0.05 g, 0.134 mmol) was reacted with m-O2N-C6H4B(OH)2 (0.0268 g, 0.16 mmol) according to general procedure B to afford 5n (83%, 0.0416 g, 0.111 mmol) as yellow solid, mp = 142.5–143.5 °C. Rf = 0.28 (30:1 CHCl3/MTBE). 1H NMR (500 MHz, CDCl3): δ 8.41–8.42 (m, 1H), 8.34–8.36 (m, 1H), 7.87–7.90 (m, 1H), 7.77–7.80 (m, 1H), 7.72–7.77 (m, 2H), 7.64–7.69 (m, 1H), 7.53–7.58 (m, 2H), 7.44–7.49 (m, 3H), 7.37–7.39 (m, 1H), 6.50 (d, JH-P = 22.9 Hz, 1H). 31P{1H} NMR (202 MHz, CDCl3): δ 36.92 (s); 13C{1H} NMR (125 MHz, CDCl3): δ 155.2 (d, JC-P = 16.4 Hz, C), 148.4 (s, C), 142.1 (d, JC-P = 26.3 Hz, C), 136.5 (d, JC-P = 16.4 Hz, C), 133.8 (s, CH), 133.4 (d, JC-P = 105.4 Hz, C), 133.0 (d, JC-P = 1.8 Hz, CH), 132.6 (d, JC-P = 2.7 Hz, CH), 130.9 (d, JC-P = 10.9 Hz, 2CH), 130.1 (s, CH), 130.0 (d, JC-P = 10.9 Hz, CH), 129.7 (d, JC-P = 10.0 Hz, CH), 128.9 (d, JC-P = 10.0 Hz, 2CH), 128.7 (d, JC-P = 103.5 Hz, C), 125.4 (d, JC-P = 98.1 Hz, CH), 124.3 (s, CH), 123.5 (d, JC-P = 11.8 Hz, CH), 122.7 (s, CH). HRMS (ESI/Q-TOF) m/z: calcd for C20H15O3NP[M + H]+, 348.0789, found: 348.0790.
1,3-Diphenyl-7-methylbenzophosphole Oxide (6a)
3b (0.052 g, 0.134 mmol) was reacted with PhB(OH)2 (0.0195 g, 0.16 mmol) according to general procedure B to afford 6a (85% according to the 1H NMR spectrum, 0.0373 g) as a mixture with 5% of Ph3P(O). Rf = 0.31 (30:1 CHCl3/MTBE). 1H NMR (500 MHz, CDCl3): δ 7.79–7.83 (m, 2H), 7.52–7.55 (m, 3H), 7.43–7.50 (m, 5H), 7.36–7.40 (m, 1H), 7.26–7.28 (m, 1H), 7.14–7.16 (m, 1H), 6.31 (d, JH-P = 24.28 Hz, 1H), 2.39 (s, 3H). 31P{1H} NMR (202 MHz, CDCl3): δ 37.44 (s); 13C{1H} NMR (125 MHz, CDCl3): δ 157.9 (d, JC-P = 15.4 Hz, C), 142.3 (d, JC-P = 27.3 Hz, C), 141.5 (d, JC-P = 9.1 Hz, C), 135.2 (d, JC-P = 16.4 Hz, C), 132.8 (d, JC-P = 1.8 Hz, CH), 132.1 (d, JC-P = 3.6 Hz, CH), 131.1 (d, JC-P = 105.4 Hz, C), 133.4 (d, JC-P = 10.0 Hz, CH), 130.9 (d, JC-P = 10.9 Hz, 2CH), 129.4 (s, CH), 129.0 (d, JC-P = 103.5 Hz, C), 128.8 (d, JC-P = 12.7 Hz, 2CH), 128.7 (s, 2CH), 127.8 (s, 2CH), 122.9 (d, JC-P = 99.9 Hz, CH), 121.6 (d, JC-P = 11.8 Hz, CH), 19.3 (d, JC-P = 4.5 Hz, CH3). GC-MS (EI) m/z: 317 (23), 316 (100) (M)+, 315 (56), 300 (11), 270 (12), 269 (48), 268 (36), 276 (10), 254 (22), 253 (26), 252 (21), 239 (18), 191 (15), 189 (15), 165 (16), 77 (14). HRMS (ESI/Q-TOF) m/z: calcd for C21H17OPNa [M + Na]+, 339.0909, found: 339.0907.
7-Methyl-1-phenyl-3-(p-tolyl)benzophosphole Oxide (6b)
3b (0.052 g, 0.134 mmol) was reacted with p-TolB(OH)2 (0.0218 g, 0.16 mmol) according to general procedure B to afford 6b (70% according to the 1H NMR spectrum, 0.0336 g) as a mixture with 5% of Ph3P(O). Rf = 0.28 (30:1 CHCl3/MTBE). 1H NMR (500 MHz, CDCl3): δ 7.78–7.82 (m, 2H), 7.65–7.70 (m, 1H), 7.52–7.55 (m, 1H), 7.43–7.51 (m, 5H), 7.36–7.39 (m, 1H), 7.29–7.30 (m, 1H), 7.13–7.15 (m, 1H), 6.28 (d, JH-P = 24.29 Hz, 1H), 2.43 (s, 3H), 2.39 (s, 3H); 31P{1H} NMR (202 MHz, CDCl3): δ 37.37 (s); 13C{1H} NMR (125 MHz, CDCl3): δ 158.1 (d, JC-P = 15.4 Hz, C), 142.4 (d, JC-P = 27.3 Hz, C), 141.5 (d, JC-P = 9.1 Hz, C), 139.6 (s, C), 132.8 (d, JC-P = 1.8 Hz, CH), 132.2 (d, JC-P = 2.7 Hz, CH), 131.03 (d, JC-P = 10.0 Hz, CH), 131.0 (d, JC-P = 10.9 Hz, CH), 129.4 (s, 2CH), 128.8 (d, JC-P = 10.0 Hz, CH), 128.5 (d, JC-P = 11.8 Hz, CH), 127.8 (s, CH), 122.0 (d, JC-P = 99.9 Hz, CH), 121.7 (d, JC-P = 10.9 Hz, CH), 21.4 (s, CH3), 19.3 (d, JC-P = 4.5 Hz, CH3). GC-MS (EI) m/z: 331 (23), 330 (100) (M)+, 329 (59), 314 (19), 284 (11), 283 (43), 282 (35), 268 (18), 267 (13), 253 (16), 252 (17), 189 (16), 165 (11). HRMS (ESI/Q-TOF) m/z: calcd for C22H19OP [M + Na]+, 353.1066, found: 353.1066.
7-Methyl-1-phenyl-3-(p-anisyl)benzophosphole Oxide (6e)
3b (0.052 g, 0.134 mmol) was reacted with p-AnB(OH)2 (0.0243 g, 0.16 mmol) according to general procedure B to afford 6e as a yellowish oil (90%, 0.0418 g, 0.121 mmol). Rf = 0.26 (30:1 CHCl3/MTBE). 1H NMR (500 MHz, CDCl3): δ 7.77–7.82 (m, 2H), 7.48–7.52 (m, 3H), 7.41–7.47 (m, 2H), 7.36–7.40 (m, 1H), 7.31–7.33 (m, 1H), 7.13–7.15 (m, 1H), 7.00–7.01 (m, 2H), 6.25 (d, JH-P = 24.28 Hz, 1H), 3.89 (s, 3H), 2.39 (s, 3H). 31P{1H} NMR (202 MHz, CDCl3): δ 37.34 (s); 13C{1H} NMR (125 MHz, CDCl3): δ 160.6 (s, C), 157.6 (d, JC-P = 15.4 Hz, C), 142.2 (d, JC-P = 27.3 Hz, C), 141.4 (d, JC-P = 9.1 Hz, C), 132.7 (d, JC-P = 1.2 Hz, CH), 132.0 (d, JC-P = 2.7 Hz, CH), 131.9 (d, JC-P = 104.5 Hz, C), 131.0 (d, JC-P = 2.7 Hz, CH), 130.9 (d, JC-P = 10.9 Hz, CH), 129.3 (s, CH), 129.2 (d, JC-P = 101.7 Hz, C), 128.8 (d, JC-P = 11.8 Hz, CH), 127.5 (d, JC-P = 16.4 Hz, CH), 121.6 (d, JC-P = 10.9 Hz, CH), 121.5 (d, JC-P = 100.9 Hz, CH), 114.1 (s, CH), 55.4 (s, CH3), 19.3 (d, JC-P = 4.5 Hz, CH3). GC-MS (EI) m/z: 347 (25), 346 (100) (M)+, 345 (47), 331 (12), 330 (25), 299 (33), 298 (46), 284 (17), 283 (14), 281 (19), 287 (16), 253 (17), 252 (11), 207 (47), 178 (12), 165 (13), 134 (11), 73 (13). HRMS (ESI/Q-TOF) m/z: calcd for C22H20O2P: 347.1201; found: 347.1202.
3-(p-Hydroxyphenyl)-7-methyl-1-phenylbenzophosphole Oxide (6h)
3b (0.052 g, 0.134 mmol) was reacted with p-OH-C6H4B(OH)2 (0.0221 g, 0.16 mmol) according to general procedure B to afford 6h (84%, 0.0374 g, 0.112 mmol) as a brownish solid, mp = 135–136 °C. Rf = 0.21 (30:1 CHCl3/MTBE). 1H NMR (500 MHz, CDCl3): δ 9.36 (bs, 1H), 7.76–7.80 (m, 2H), 7.49–7.55 (m, 1H), 7.41–7.47 (m, 2H), 7.29–7.40 (m, 4H), 7.09–7.12 (m, 1H), 7.00–7.02 (m, 2H), 6.14 (d, JH-P = 24.59 Hz, 1H), 2.36 (s, 3H); 31P{1H} NMR (202 MHz, CDCl3): δ 38.98 (s); 13C{1H} NMR (125 MHz, CDCl3): δ 158.9 (s, C), 158.8 (d, JC-P = 15.4 Hz, C), 142.5 (d, JC-P = 28.16 Hz, C), 141.4 (d, JC-P = 9.1 Hz, C), 132.9 (s, CH), 132.3 (d, JC-P = 1.8 Hz, CH), 131.1 (d, JC-P = 7.2 Hz, CH), 131.0 (d, JC-P = 10.9 Hz, CH), 129.3 (s, CH), 128.9 (d, JC-P = 11.8 Hz, CH), 125.8 (d, JC-P = 16.4 Hz, CH), 122.0 (d, JC-P = 10.9 Hz, CH), 119.7 (d, JC-P = 101.7 Hz, CH), 116.0 (s, CH), 19.6 (d, JC-P = 4.5 Hz, CH3). HRMS (ESI/Q-TOF) m/z: calcd for C21H18O2P [M + H]+, 333.1044, found: 333.1044.
3-(m-Aminophenyl)-7-methyl-1-phenylbenzophosphole Oxide (6i)
3b (0.052 g, 0.134 mmol) was reacted with m-H2N-C6H4B(OH)2-H2O (0.0248 g, 0.16 mmol) according to general procedure B to afford 6i (96%, 0.0424 g, 0.128 mmol) as a brownish solid, mp = 171.3–172.1 °C. Rf = 0.43 (30:5:1 CHCl3/AcOEt/MeOH). 1H NMR (500 MHz, CDCl3): δ 7.77–7.81 (m, 2H), 7.51–7.54 (m, 1H), 7.42–7.46 (m, 2H), 7.30–7.38 (m, 2H), 7.23–7.26 (m, 1H), 7.11–7.14 (m, 1H), 6.89–6.92 (m, 1H), 6.76–6.82 (m, 2H), 6.26 (d, JH-P = 24.43 Hz, 1H), 3.85 (m, 2H), 2.38 (s, 3H). 31P{1H} NMR (202 MHz, CDCl3): δ 37.37 (s); 13C{1H} NMR (125 MHz, CDCl3): δ 158.2 (d, JC-P = 15.4 Hz, C), 146.8 (s, C), 142.3 (d, JC-P = 28.2 Hz, C), 141.3 (d, JC-P = 9.1 Hz, C), 136.2 (d, JC-P = 16.4 Hz, C), 132.7 (d, JC-P = 1.8 Hz, CH), 132.2 (d, JC-P = 2.7 Hz, CH), 131.8 (d, JC-P = 104.5 Hz, C), 130.96 (d, JC-P = 9.1 Hz, CH), 130.9 (d, JC-P = 10.9 Hz, CH), 129.6 (s, CH), 129.2 (d, JC-P = 101.7 Hz, C), 128.8 (d, JC-P = 12.7 Hz, CH), 122.4 (d, JC-P = 99.9 Hz, CH), 121.8 (d, JC-P = 11.8 Hz, CH), 117.9 (s, CH), 115.9 (s, CH), 114.1 (s, CH), 19.3 (d, JC-P = 4.5 Hz, CH3). GC-MS (EI) m/z: 332 (18), 331 (75) (M)+, 330 (32), 316 (8), 315 (27), 285 (14), 284 (55), 283 (22), 282 (18), 281 (41), 269 (15), 268 (15), 267 (21), 253 (16), 252 (12), 209 (15), 208 (22), 207 (100), 193 (12), 191 (17), 165 (13), 135 (13), 134 (18), 96 (12), 77 (11). HRMS (ESI/Q-TOF) m/z: calcd for C21H19ONP [M + H]+, 332.1204, found: 332.1206.
3-(p-Fluorophenyl)-7-methyl-1-phenylbenzophosphole Oxide (6j)
3b (0.052 g, 0.134 mmol) was reacted with p-F-C6H4B(OH)2 (0.0223 g, 0.16 mmol) according to general procedure B to afford 6j (84% according to the 1H NMR spectrum, 0.0394 g) as a mixture with 5% of Ph3P(O). Rf = 0.21 (30:1 CHCl3/MTBE). 1H NMR (500 MHz, CDCl3): δ 7.77–7.81 (m, 2H), 7.50–7.56 (m, 3H), 7.43–7.47 (m, 2H), 7.37–7.40 (m, 1H), 7.22–7.24 (m, 1H), 7.15–7.20 (m, 3H), 6.29 (d, JH-P = 23.7 Hz, 1H), 2.39 (s, 3H); 31P{1H} NMR (202 MHz, CDCl3): δ 37.23 (s); 13C{1H} NMR (125 MHz, CDCl3): δ 163.2 (d, JC-F = 248.9 Hz, C-F), 156.8 (d, JC-P = 15.4 Hz, C), 142.1 (d, JC-P = 27.3 Hz, C), 141.6 (d, JC-P = 9.1 Hz, C), 132.8 (d, JC-P = 1.8 Hz, CH), 132.2 (d, JC-P = 3.6 Hz, CH), 131.6 (d, JC-P = 103.6 Hz, C), 131.2 (d, JC-P = 10.0 Hz, CH), 130.9 (d, JC-P = 10.9 Hz, 2CH), 129.7 (d, JC-F = 7.2 Hz, 2CH), 129.1 (d, JC-P = 101.7 Hz, C), 128.8 (d, JC-P = 11.8 Hz, 2CH), 123.2 (d, JC-P = 99.0 Hz, CH), 121.4 (d, JC-P = 10.9 Hz, CH), 115.8 (d, JC-F = 21.8 Hz, 2CH), 19.3 (d, JC-P = 4.5 Hz, CH3). GC-MS (EI) m/z: 335 (20), 334 (90) (M)+, 333 (47), 318 (17), 288 (11), 287 (43), 286 (40), 285 (11), 283 (14), 282 (12), 281 (37), 272 (19), 271 (23), 270 (19), 257 (17), 253 (13), 214 (14), 210 (10), 209 (23), 208 (24), 207 (100), 191 (19), 189 (11), 183 (13), 135 (11), 133 (19), 96 (14), 77 (12), 73 (29). HRMS (ESI/Q-TOF) m/z: calcd for C21H17OFP [M + H]+, 335.1001, found: 335.1002.
3-(m-Nitrophenyl)-7-methyl-1-phenylbenzophosphole Oxide (6n)
3b (0.052 g, 0.134 mmol) was reacted with m-O2N-C6H4B(OH)2 (0.0268 g, 0.16 mmol) according to general procedure B to afford 6n (99%, 0.0479 g, 0.133 mmol) as a yellowish solid, mp = 207–208 °C. Rf = 0.23 (30:1 CHCl3/MTBE). 1H NMR (500 MHz, CDCl3): δ 8.39–8.41 (m, 1H), 8.33–8.36 (m, 1H), 7.86–7.88 (m, 1H), 7.78–7.82 (m, 2H), 7.69–7.72 (m, 1H), 7.56–7.60 (m, 1H), 7.46–7.50 (m, 2H), 7.41–7.46 (m, 1H), 7.16–7.23 (m, 2H), 6.44 (d, JH-P = 23.01 Hz, 1H), 2.41 (s, 3H). 31P{1H} NMR (202 MHz, CDCl3): δ 37.15 (s); 13C{1H} NMR (125 MHz, CDCl3): δ 155.1 (d, JC-P = 16.4 Hz, C), 148.4 (s, C), 142.1 (d, JC-P = 9.1 Hz, C), 141.3 (d, JC-P = 27.2 Hz, C), 136.8 (d, JC-P = 17.2 Hz, C), 133.8 (s, CH), 133.1 (d, JC-P = 1.8 Hz, CH), 132.5 (d, JC-P = 3.6 Hz, CH), 131.6 (d, JC-P = 10.0 Hz, CH), 130.9 (d, JC-P = 10.9 Hz, CH), 130.1 (s, CH), 129.0 (d, JC-P = 12.7 Hz, CH), 125.5 (d, JC-P = 98.1 Hz, CH), 124.2 (s, CH), 122.8 (s, CH), 121.7 (d, JC-P = 10.9 Hz, CH), 19.4 (d, JC-P = 4.5 Hz, CH3). HRMS (ESI/Q-TOF) m/z: calcd for C21H17NO3 [M + H]+, 331.1208, found: 331.1208.
6-Chloro-1,3-diphenylbenzophosphole Oxide (7a)
3c (0.0547 g, 0.134 mmol) was reacted with PhB(OH)2 (0.0195 g, 0.16 mmol) according to general procedure B to afford 7a as a yellowish oil (68%, 0.0307 g, 0.0911 mmol). Rf = 0.31 (30:1 CHCl3/MTBE). 1H NMR (500 MHz, CDCl3): δ 7.77–7.82 (m, 2H), 7.63–7.65 (m, 1H), 7.55–7.60 (m, 1H), 7.49–7.55 (m, 8H), 7.40–7.42 (m, 1H), 6.39 (d, JH-P = 24.28 Hz, 1H). 31P{1H} NMR (202 MHz, CDCl3): δ 36.04 (s); 13C{1H} NMR (125 MHz, CDCl3): δ 157.6 (d, JC-P = 14.5 Hz, C), 140.2 (d, JC-P = 26.4 Hz, C), 136.3 (d, JC-P = 100.8 Hz, C), 136.1 (d, JC-P = 14.5 Hz, CH), 134.5 (d, JC-P = 16.5 Hz, CH), 133.9 (d, JC-P = 10.9 Hz, CH), 132.6 (d, JC-P = 2.7 Hz, CH), 132.4 (d, JC-P = 1.8 Hz, CH), 130.9 (d, JC-P = 10.9 Hz, CH), 129.8 (s, CH), 129.5 (d, JC-P = 10.9 Hz, CH), 129.0 (d, JC-P = 12.7 Hz, CH), 128.9 (s, 2CH), 127.7 (s, 2CH), 125.1 (d, JC-P = 11.8 Hz, CH), 122.8 (d, JC-P = 99.9 Hz, CH). HRMS (ESI/Q-TOF) m/z: calcd for C20H15ClOP [M + H]+, 337.0549; found: 337.0548.
1,3-Diphenyl-5-methoxybenzophosphole Oxide (8a)
3d (0.0542 g, 0.134 mmol) was reacted with PhB(OH)2 (0.0195 g, 0.16 mmol) according to general procedure B to afford 8a (90% according to the 1H NMR spectrum, 0.0436 g) as a mixture with 7% of Ph3P(O). Rf = 0.22 (30:1 CHCl3/MTBE). 1H NMR (500 MHz, CDCl3): δ 7.76–7.80 (m, 2H), 7.62–7.64 (m, 1H), 7.44–7.55 (m, 8H), 7.00–7.01 (m, 1H), 6.88–6.89 (m, 1H), 6.39 (d, JH-P = 23.64 Hz, 1H), 3.82 (s, 3H). 31P{1H} NMR (202 MHz, CDCl3): δ 36.07 (s); 13C{1H} NMR (125 MHz, CDCl3): δ 163.5 (s, C), 157.2 (d, JC-P = 14.5 Hz, C), 144.5 (d, JC-P = 29.1 Hz, C), 134.8 (d, JC-P = 16.4 Hz, C), 132.1 (d, JC-P = 2.7 Hz, CH), 130.9 (d, JC-P = 10.9 Hz, 2CH), 130.8 (d, JC-P = 10.9 Hz, CH), 129.1 (d, JC-P = 104.5 Hz, C), 129.5 (s, CH), 128.8 (s, CH), 127.7 (d, JC-P = 12.7 Hz, 2CH), 127.8 (s, 2CH), 124.4 (d, JC-P = 111.7 Hz, C), 125.3 (d, JC-P = 99.0 Hz, CH), 112.9 (d, JC-P = 11.8 Hz, CH), 111.9 (d, JC-P = 12.7 Hz, CH), 55.6 (s, CH3). GC-MS (EI) m/z: 333 (4), 332 (100) (M)+, 331 (44), 317 (16), 316 (67), 315 (14), 301 (14), 285 (31), 271 (11), 270 (31), 255 (35), 252 (17), 241 (14), 240 (13), 239 (50), 220 (11), 183 (19), 165 (32), 152 (13), 139 (10), 77 (15). HRMS (ESI/Q-TOF) m/z: calcd for C21H18O2P [M + H]+, 333.1044, found: 333.1044.
1-Phenyl-5-methoxy-3-(p-tolyl)benzophosphole Oxide (8b)
3d (0.0542 g, 0.134 mmol) was reacted with p-TolB(OH)2 (0.0218 g, 0.16 mmol) according to general procedure B to afford 8b (81% according to the 1H NMR spectrum, 0.0418 g) as a mixture with 7% of Ph3P(O). Rf = 0.53 (30:5:1 CHCl3/AcOEt/MeOH). 1H NMR (500 MHz, CDCl3): δ 7.75–7.79 (m, 2H), 7.59–7.63 (m, 1H), 7.51–7.54 (m, 1H), 7.42–7.45 (m, 4H), 7.29–7.31 (m, 2H), 7.02–7.03 (m, 1H), 6.88–6.89 (m, 1H), 6.36 (d, JH-P = 23.80 Hz, 1H), 3.82 (s, 3H), 2.44 (s, 3H). 31P{1H} NMR (202 MHz, CDCl3): δ 36.07 (s); 13C{1H} NMR (125 MHz, CDCl3): δ 163.5 (d, JC-P = 1.8 Hz, C), 157.3 (d, JC-P = 14.5 Hz, C), 144.6 (d, JC-P = 29.1 Hz, C), 139.7 (s, CH), 132.1 (d, JC-P = 2.7 Hz, CH), 132.0 (d, JC-P = 4.5 Hz, CH), 130.9 (d, JC-P = 10.9 Hz, 2CH), 130.8 (d, JC-P = 11.8 Hz, CH), 129.9 (d, JC-P = 104.5 Hz, C), 129.5 (s, 2CH), 128.7 (d, JC-P = 12.7 Hz, 2CH), 127.7 (s, 2CH), 124.5 (d, JC-P = 111.7 Hz, C), 123.7 (d, JC-P = 99.0 Hz, CH), 112.9 (d, JC-P = 11.8 Hz, CH), 111.9 (d, JC-P = 11.8 Hz, CH), 55.5 (s, CH3), 21.3 (s, CH3). GC-MS (EI) m/z: 347 (5), 346 (19) (M)+, 345 (12), 330 (19), 283 (11), 282 (13), 281 (46), 267 (12), 253 (19), 209 (15), 208 (23), 207 (100), 193 (10), 191 (13), 147 (12), 135 (12), 133 (14), 95 (13), 73 (36). HRMS (ESI/Q-TOF) m/z: calcd for C22H20O2P [M + H]+, 347.1201, found: 347.1202.
3-(p-Hydroxyphenyl)-1-phenyl-5-methoxybenzophosphole Oxide (8h)
3d (0.0542 g, 0.134 mmol) was reacted with p-OH-C6H4B(OH)2 (0.0221 g, 0.16 mmol) according to general procedure B to afford 8h (73%, according to the 1H NMR spectrum, 0.035 g) as a pale yellow solid, mp = 248.4–249.6 °C. Rf = 0.26 (30:5:1 CHCl3/AcOEt/MeOH). 1H NMR (500 MHz, CDCl3): δ 7.74–7.79 (m, 2H), 7.58–7.61, (m, 1H), 7.52–7.54 (m, 1H), 7.42–7.46 (m, 2H), 7.34–7.36 (m, 2H), 7.07–7.08 (m, 1H), 7.01–7.03 (m, 2H), 6.85–6.89 (m, 1H), 6.24 (d, JH-P = 24.12 Hz, 1H), 3.81 (s, 3H). 31P{1H} NMR (202 MHz, CDCl3): δ 37.76 (s); 13C{1H} NMR (125 MHz, CDCl3): δ 163.4 (s, C), 159.1 (s, C), 158.2 (d, JC-P = 15.4 Hz, C), 144.8 (d, JC-P = 29.9 Hz, C), 132.3 (d, JC-P = 2.7 Hz, CH), 130.9 (d, JC-P = 10.9 Hz, CH), 130.8 (d, JC-P = 11.8 Hz, CH), 129.3 (d, JC-P = 103.5 Hz, C), 129.2 (s, CH), 128.8 (d, JC-P = 12.7 Hz, CH), 125.4 (d, JC-P = 17.3 Hz, C), 123.8 (d, JC-P = 112.6 Hz, C), 120.0 (d, JC-P = 101.7 Hz, CH), 116.1 (s, CH), 113.2 (d, JC-P = 11.8 Hz, CH), 112.1 (d, JC-P = 12.7 Hz, CH), 55.6 (s, CH3). HRMS (ESI/Q-TOF) m/z: calcd for C21H18O3P [M + H]+, 349.0994, found: 349.0995.
3-(m-Aminophenyl)-5-methoxy-1-phenylbenzophosphole Oxide (8i)
3d (0.0542 g, 0.134 mmol) was reacted with m-H2N-C6H4B(OH)2-H2O (0.0248 g, 0.16 mmol) according to general procedure B to afford 8i (85%, 0.0395 g, 0.114 mmol) as an orange oil. Rf = 0.33 (30:5:1 CHCl3/AcOEt/MeOH). 1H NMR (500 MHz, CDCl3): δ 7.72–7.77 (m, 2H), 7.57–7.59 (m, 1H), 7.49–7.53 (m, 1H), 7.40–7.43 (m, 2H), 7.23–7.25 (m, 1H), 7.03–7.04 (m, 1H), 6.79–6.91 (m, 4H), 6.32 (d, d, JH-P = 23.96 Hz, 1H), 4.07 (bs, 1H), 3.80 (s, 3H). 31P{1H} NMR (202 MHz, CDCl3): δ 35.89 (s); 13C{1H} NMR (125 MHz, CDCl3): δ 163.5 (d, JC-P = 1.8 Hz, C), 157.4 (d, JC-P = 14.5 Hz, C), 146.3 (s, C), 144.6 (d, JC-P = 28.2 Hz, C), 135.9 (d, JC-P = 16.4 Hz, C), 132.0 (d, JC-P = 2.7 Hz, CH), 130.9 (d, JC-P = 10.9 Hz, 2CH), 130.6 (d, JC-P = 10.9 Hz, CH), 129.6 (s, CH), 128.7 (d, JC-P = 10.9 Hz, 2CH), 124.4 (d, JC-P = 111.7 Hz, C), 123.9 (d, JC-P = 99 Hz, CH), 118.2 (s, CH), 116.4 (s, CH), 112.9 (d, JC-P = 11.8 Hz, CH), 111.9 (d, d, JC-P = 11.8 Hz, CH), 55.6 (s, CH3). HRMS (ESI/Q-TOF) m/z: calcd for C21H19O2NP [M + H]+, 348.1204, found: 348.1204.
1-Phenyl-5-methoxy-3-(p-nitrophenyl)benzophosphole Oxide (8n)
3d (0.0542 g, 0.134 mmol) was reacted with m-O2N-C6H4B(OH)2 (0.0268 g, 0.16 mmol) according to general procedure B to afford 8n (88% according to the 1H NMR spectrum, 0.047 g) as a mixture with 5% of Ph3P(O). Rf = 0.21 (30:1 CHCl3/MTBE). 1H NMR (500 MHz, CDCl3): δ 8.34–8.40 (m, 2H), 7.86–7.88 (m, 1H), 7.73–7.79 (m, 2H), 7.66–7.71 (m, 2H), 7.55–7.59 (m, 1H), 7.45–7.49 (m, 2H), 6.92–6.94 (m, 1H), 6.87–6.88 (m, 1H), 6.52 (d, JH-P = 22.54 Hz, 1H), 3.85 (s, 3H). 31P{1H} NMR (202 MHz, CDCl3): δ 35.58 (s); 13C{1H} NMR (125 MHz, CDCl3): δ 163.8 (d, JC-P = 1.8 Hz, C), 154.3 (d, JC-P = 16.4 Hz, C), 148.5 (s, C), 143.5 (d, JC-P = 28.2 Hz, C), 136.5 (d, JC-P = 16.4 Hz, C), 133.8 (s, CH), 132.4 (d, JC-P = 2.7 Hz, CH), 132.1 (d, JC-P = 10.0 Hz, CH), 131.4 (d, JC-P = 11.8 Hz, CH), 131.0 (d, JC-P = 10.9 Hz, 2CH), 130.1 (s, CH), 128.9 (d, JC-P = 12.7 Hz, 2CH), 127.0 (d, JC-P = 97.2 Hz, CH), 124.2 (s, CH), 123.9 (d, JC-P = 112.6 Hz, C), 122.8 (s, CH), 113.2 (d, JC-P = 11.8 Hz, CH), 111.5 (d, JC-P = 11.8 Hz, CH), 55.7 (s, CH3). HRMS (ESI/LQT) m/z: calcd for C21H17O4NP [M + H]+, 378.0895, found: 378.0894.
C: Procedure for the Reaction of 3b with 4n in a Higher Scale
To a reaction vial (30 mL) equipped with a magnetic stirrer and an argon inlet, 3b (0.389 g, 1 mmol), m-NO2-C6H4B(OH)2 (4n) (0.2 g, 1.2 mmol), K2CO3 (0.276 g, 2.0 mmol), and Pd(PPh3)4 (58.0 mg, 0.05 mmol) were added followed by DME (10 mL). The vial was closed using an aluminum cap and heated at 110 °C using heating transfer blocks for 24 h. After that time, the reaction was cooled to rt, and the solvent was evaporated. To the residue, a saturated solution of NaHCO3 (10 mL) and DCM (10 mL) was added, and the mixture was transferred to an extraction funnel. The mixture was extracted with DCM (3 × 15 mL), and the collected organic phases were dried over Na2SO4. The solid was filtered off, and the filtrate evaporated under reduced pressure. The crude reaction mixture was checked using the NMR technique. The crude product was purified by column chromatography on silica gel using CHCl3/MTBE (30:1 v/v) as the eluent.
3-(m-Nitrophenyl)-7-methyl-1-phenylbenzophosphole Oxide (6n)
3b was reacted according to general procedure C to afford 6n (91%, 0.329 g, 0.91 mmol).
D: Procedure for the Reaction of 3a with 4a Using Pd(PPh3)4 in Different Solvents (Table 1, Entries 1–11)
To a reaction vial (5 mL) equipped with a magnetic stirrer and an argon inlet, 3a (0.0375 g, 0.1 mmol), PhB(OH)24a (0.0195 g, 0.12 mmol), base (0.2 mmol), and Pd(PPh3)4 (7.7 mg, 5.0 μmol) were added followed by the solvent (1 mL). The vial was closed using an aluminum cap and heated at indicated temperature using heating blocks for 24 h. After that time, the reaction was cooled to rt, and the solvent was evaporated. To the residue, a saturated solution of NaHCO3 (5 mL) and DCM (10 mL) were added, and the mixture was transferred to an extraction funnel. The mixture was extracted with DCM (3 × 15 mL), and the collected organic phases were dried over Na2SO4. The solid was filtered off, and the filtrate evaporated under reduced pressure. The crude reaction mixture was checked using the NMR technique. The crude product was purified by column chromatography on silica gel using CHCl3/MTBE (30:1 v/v) as an eluent.
1,3-Diphenylbenzophosphole Oxide (5a)13
3a was reacted according to procedure D using K2CO3 (0.0276 g, 0.2 mmol) as a base in DMF at 110 °C to afford 5a (85%, 0.026 g, 0.085 mmol).
1,3-Diphenylbenzophosphole Oxide (5a)13
3a was reacted according to procedure D using K2CO3 (0.0276 g, 0.2 mmol) as a base in THF at 60 °C to afford 5a (57%, 0.0172 g, 0.057 mmol).
1,3-Diphenylbenzophosphole Oxide (5a)13
3a was reacted according to procedure D using K2CO3 (0.0276 g, 0.2 mmol) as a base in toluene at 80 °C to afford 5a (52%, 0.0157 g, 0.052 mmol).
1,3-Diphenylbenzophosphole Oxide (5a)13
3a was reacted according to procedure D using K2CO3 (0.0276 g, 0.2 mmol) as a base in toluene at 110 °C to afford 5a (87%, 0.0263 g, 0.087 mmol).
1,3-Diphenylbenzophosphole Oxide (5a)13
3a was reacted according to procedure D using K2CO3 (0.0276 g, 0.2 mmol) as a base in 1,4-dioxane at rt to afford 5a (79%, 0.0239 g, 0.079 mmol).
1,3-Diphenylbenzophosphole Oxide (5a)13
3a was reacted according to procedure D using K2CO3 (0.0276 g, 0.2 mmol) as a base in 1,4-dioxane at 80 °C to afford 5a (74%, 0.0224 g, 0.074 mmol).
1,3-Diphenylbenzophosphole Oxide (5a)13
3a was reacted according to procedure D using K2CO3 (0.0276 g, 0.2 mmol) as a base in DME at 50 °C to afford 5a (55%, 0.0166 g, 0.055 mmol).
1,3-Diphenylbenzophosphole Oxide (5a)13
3a was reacted according to procedure D using K2CO3 (0.0276 g, 0.2 mmol) as a base in DME at 80 °C to afford 5a (61%, 0.0184 g, 0.061 mmol).
1,3-Diphenylbenzophosphole Oxide (5a)13
3a was reacted according to procedure D using Na2CO3 (0.1 mL, 0.2 mmol, 2 M) as a base in DME at 110 °C to afford 5a (62%, 0.0187 g, 0.062 mmol).
1,3-Diphenylbenzophosphole Oxide (5a)13
3a was reacted according to procedure D using Na2CO3 (0.1 mL, 0.2 mmol, 2 M) as a base and LiCl (0.0127 g, 0.3 mmol) in DME at 110 °C to afford 5a (60%, 0.0181 g, 0.06 mmol).
E: Procedure for the Reaction of 3a with 4a Using Pd(OAc)2 as a Catalyst (Table 1, Entries 12–13)
To a reaction vial (5 mL) equipped with a magnetic stirrer and an argon inlet, 3a (0.1 g, 0.268 mmol), PhB(OH)2 (4a) (0.039 g, 0.32 mmol), KF (0.031 g, 0.543 mmol), Pd(OAc)2 (1.2 mg, 5.3 μmol), and ligand (6.4 μmol) were added followed by the solvent (1 mL). The vial was closed using an aluminum cap and heated at 85 °C using heating transfer blocks for 24 h or stirred at rt for 24 h. After that time, the solvent was evaporated. To the residue, a saturated solution of NaHCO3 (5 mL) and DCM (10 mL) was added, and the mixture was transferred to an extraction funnel. The mixture was extracted with DCM (3 × 10 mL), and the collected organic phases were dried over Na2SO4. The solid was filtered off and the filtrate was evaporated under reduced pressure. The crude reaction mixture was checked using the NMR technique. The crude product was purified by column chromatography on silica gel using CHCl3/MTBE (30:1 v/v) as an eluent.
1,3-Diphenylbenzophosphole Oxide (5a)13
3a was reacted according to procedure E using PCy3 (1.8 mg, 6.4 μmol) as a ligand in DME at 85 °C for 24 h to afford 5a (21%, 0.0167 g, 0.056 mmol).
1,3-Diphenylbenzophosphole Oxide (5a)13
3a was reacted according to procedure E using PTol3 (2.0 mg, 6.4 μmol) as a ligand in THF at rt for 24 h to afford 5a (17%, 0.0137 g, 0.0454 mmol) and 2a (24%, 0.011 g, 0.045 mmol).
1-Phenylbenzophosphole Oxide (2a)42
1H NMR (500 MHz, CDCl3): δ 8.05–8.07 (m, 1H), 7.85–7.90 (m, 1H), 7.77–7.83 (m, 2H), 7.55–7.60 (m, 3H), 7.45–7.47 (m, 2H), 3.12–3.31 (m, 2H). 31 P NMR (202 MHz, CDCl3): δ 29.92 (s). 13C NMR (125 MHz, CDCl3): δ 194.3 (d, JC-P = 12.7 Hz, C), 141.5 (d, JC-P = 80.8 Hz, C), 141.3 (d, JC-P = 23.6 Hz, C), 135.9 (d, JC-P = 10.9 Hz, CH), 133.6 (d, JC-P = 2.7 Hz, CH), 132.6 (d, JC-P = 2.7 Hz, CH), 130.8 (d, JC-P = 105.4 Hz, C), 130.6 (d, JC-P = 10.9 Hz, 2CH), 129.4 (d, JC-P = 6.4 Hz, CH), 128.9 (d, JC-P = 13.6 Hz, 2CH), 124.7 (d, JC-P = 10.9 Hz, CH), 40.1 (d, JC-P = 71.8 Hz, CH2).
F: Procedure for the Reaction of 3a with 4a Using PdCl2 as a Catalyst (Table 1, Entry 14)
To a reaction vial (5 mL) equipped with a magnetic stirrer and an argon inlet, 3a (0.1 g, 0.268 mmol), PhB(OH)2 (4a) (0.039 g, 0.32 mmol), Na2CO3 (0.0566 g, 0.543 mmol), PdCl2 (2.4 mg, 13.3 μmol), and PTol3 (4.1 mg, 13.3 μmol) were added followed by THF (1 mL). The vial was closed and heated at 40 °C using an oil bath for 24 h. After that time, the reaction was cooled to rt, and the solvent was evaporated. To the residue, a saturated solution of NaHCO3 (5 mL) and DCM (10 mL) was added, and the mixture was transferred to an extraction funnel. The mixture was extracted with DCM (3 × 10 mL), and the collected organic phases were dried over Na2SO4. The solid was filtered off, and the filtrate evaporated under reduced pressure. The crude reaction mixture was checked using the NMR technique. The crude product was purified by column chromatography on silica gel using CHCl3/MTBE (30:1 v/v) as an eluent.
1,3-Diphenylbenzophosphole Oxide (5a)13
3a was reacted according to procedure F to afford 5a (13%, 0.0105 g, 0.0345 mmol) and 2a (13%, 0.008 g, 0.0345 mmol).
Acknowledgments
This work was partially supported by a grant from the National Center of Science (Narodowe Centrum Nauki) in Poland (proj. no. 2018/02/X/ST5/00635) and standard university statutory funding. Ł.P. thanks for financial support of these studies from the Gdańsk University of Technology by the DEC-2/2021/IDUB/V.6/Si grant under the SILICIUM SUPPORTING CORE R&D FACILITIES—“Excellence Initiative—Research University” program is gratefully acknowledged. S.S. wishes to thank Dr. Rafał Typek from the Department of Chromatographic Methods (Maria Curie-Sklodowska University in Lublin) for some HRMS measurements. S.S. wants to thank Prof. Marta Arczewska from the Department of Biophysics (the University of Life Sciences in Lublin) for the possibility of carrying out some comparison measurements and discussion. The authors want to thank Prof. Marek Majdan from the Department of Inorganic Chemistry (Maria Curie-Sklodowska University in Lublin) and Prof. Piotr Borowski from the Department of Theoretical Chemistry (Maria Curie-Sklodowska University in Lublin) for the useful suggestions regarding fluorescence and DFT calculations. S.S. wants to thank Prof. Christian Hackenberger from Chemical Biology II (Leibniz-Research Institute for Molecular Pharmacology and the Humboldt Universität zu Berlin) (Germany) for kindly reading the manuscript and Dr. Duncan Carmichael from Laboratoire “Hétéroéléments et Coordination”, Ecole Polytechnique, CNRS, Palaiseau (France) for lexical and grammar evaluation. The authors want to thank all of the anonymous reviewers for all of the knowledge and advice they shared with us.
Data Availability Statement
The data underlying this study are available in the published article and its Supporting Information.
Supporting Information Available
The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.joc.2c02355.
1H NMR, 13C{1H} NMR, and 31P{1H} NMR spectra for all products (2a, 5a–n, 6a–b,e,h–j,n, 7a, 8a–b,h–i,n) and starting materials (3a–d); crystallographic data (3d, 5n, 6n); and data/figures obtained from DFT and TD-DFT calculations at the B3LYP/6–31+G(d,p) level of theory (PDF)
Author Contributions
S.S.: Conceptualization; S.M. and S.S.: investigation; A.B.: DFT calculations; A.B. and S.S.: interpretation; Ł.P.: X-ray analysis and interpretation; A.L., A.G.-P., M.Z.-D., and S.S.: absorption and emission measurements; S.S. and A.L.: interpretation; S.S.: writing-original draft; S.S.: writing-review; S.S., A.B., Ł.P., M.Z.-D., and A.L: editing. All authors have read and agreed to the published version of the manuscript.
The authors declare no competing financial interest.
Supplementary Material
References
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Data Availability Statement
The data underlying this study are available in the published article and its Supporting Information.