The Reactivity of Phosphanylphosphinidene Complexes of Transition Metals Toward Terminal Dihaloalkanes

Abstract

The reactivities of phosphanylphosphinidene complexes [(DippN)₂W(Cl)(η²-P–PtBu₂)]⁻ (1), [(pTol₃P)₂Pt(η²-P=PtBu₂)] (2), and [(dppe)Pt(η²-P=PtBu₂)] (3) toward dihaloalkanes and methyl iodide were investigated. The reactions of the anionic tungsten complex (1) with stochiometric Br(CH₂)_nBr (n = 3, 4, 6) led to the formation of neutral complexes with a tBu₂PP(CH₂)₃Br ligand or neutral dinuclear complexes with unusual tetradentate tBu₂PP(CH₂)_nPPtBu₂ ligands (n = 4, 6). The methylation of platinum complexes 2 and 3 with MeI yielded neutral or cationic complexes bearing side-on coordinated tBu₂P–P-Me moieties. The reaction of 2 with I(CH₂)₂I gave a platinum complex with a tBu₂P—P—I ligand. When the same dihaloalkane was reacted with 3, the P—P bond in the phosphanylphosphinidene ligand was cleaved to yield tBu₂PI, phosphorus polymers, [(dppe)PtI₂] and C₂H₄. Furthermore, the reaction of 3 with Br(CH₂)₂Br yielded dinuclear complex bearing a tetraphosphorus tBu₂PPPPtBu₂ ligand in the coordination sphere of the platinum. The molecular structures of the isolated products were established in the solid state and in solution by single-crystal X-ray diffraction and NMR spectroscopy. DFT studies indicated that the polyphosphorus ligands in the obtained complexes possess structures similar to free phosphenium cations tBu₂P⁺=P−R (R = Me, I) or (tBu₂P⁺=P)₂.

Short abstract

The phosphanylphosphinidene complexes of tungsten and platinum as building blocks for syntheses of polydentate phosphorus ligands.

1. Introduction

The properties of phosphido and phosphinidene complexes of transition metals (TM) as synthetic tools in organic and inorganic chemistry have recently been intensely studied.¹ Formally, phosphinidene complexes can be divided into two classes: electrophilic, which are often very reactive transient species²⁻⁶ except for the stable phosphinidene complexes of cobalt and vanadium described by Carty group,^7,8 and nucleophilic, which are generally isolable.^5,6,9 It is commonly accepted that the electrophilicity versus nucleophilicity of a phosphinidene complex is primarily determined by the electronic properties of the spectator ligands¹⁰–acceptor ligands (especially CO) that result in electrophilic complexes, whereas donor spectator ligands, such as NR and PR₃, result in nucleophilic complexes. From this point of view, phosphanylphosphinidene complexes, which we discuss in this paper ([(DippN)₂W(Cl)(η²-P–PtBu₂)]⁻ (1),¹¹ [(pTol₃P)₂Pt(η²-P=PtBu₂)] (2),¹² and [(dppe)Pt(η²-P=PtBu₂)] (3)¹³) must be considered nucleophilic species (Scheme 1). Similar nucleophilic phosphanylphosphinidene complexes [(η²-R₂PP)Nb{N(Np)(3,5-Me₂-C₆H₃)}₃] and [(η²-R₂PP)W{N(iPr)(3,5-Me₂-C₆H₃)}₃]⁺ were studied by Cummins group.^14,15

Scheme 1. Phosphanylphosphinidene Complexes of W and Pt Used for Reactivity Studies.

The nucleophilicity of these species can also be enhanced by a donor phosphanyl group (PtBu₂) in the phosphinidene ligand. It should be stressed that stable phosphanylphosphinidene R₂P=P (R = nitrogen-based very bulky group) is singlet and electrophilic.¹⁶ Reactivity studies on tBu₂P–P=PtBu₂(Me)¹⁷ and DFT-calculations¹⁸ revealed that transient tBu₂P–P is also electrophilic. The nucleophilic phosphinidene complexes of early TM have been intensely studied and explored as P–R transfer vehicles to organic or inorganic molecules (phospha-Wittig reactivity). The first report concerned reactions of [(N₃N)Ta^V=PR], N₃N = (Me₃SiNCH₂CH₂)₃N (κ³-N-chelating ligand) with aldehydes yielding the corresponding phosphenes.¹⁹ Phosphinidene ate complex [(PNP)Sc^III(=PDmp)·LiBr] can transfer its P-Dmp moiety even to a Cp₂Zr-center, resulting in [Cp₂Zr^IV(=PDmp)(PMe₃)]. However, the analogous phosphinidene transfer was not observed for the reaction involving a Cp₂Ti-center.²⁰ Similarly, zirconium complexes [Cp*₂Zr(PPh)₂] and [Cp*₂Zr(PPh)₃] do not display phospha-Wittig reactivity.²¹ Otherwise, [Cp₂Zr^IV(=PDmp)(PMe₃)] itself displayed high reactivity toward electrophilic reagents.²² Similarly, [Cp₂Zr^IV(=PMes*)(PMe₃)] showed high phospha-Wittig reactivity and converted aldehydes and ketones into phosphenes. It reacted with CH₂Cl₂ and CHCl₃ yielding the related phosphenes as well.²³ Recently, the high reactivity of the phosphido complex [^MeNacNacTi^III(Cl)(η²-(Me₃Si)P–PR₂)] R₂ = tBu₂ or tBu(Ph) toward acetone, yielding Wittig products R₂P–P=C(CH₃)₂ was established.²⁴ The reactivity of nucleophilic phosphinidene complexes of iron, iridium, and platinum toward electrophilic reagents was briefly studied. Dinuclear complexes [Fe₂(η-PR)(η-CO)(CO)₂] (R = cHex or Ph) reacted with MeI, yielding related [Fe₂{η-P(Me)R}(η-CO)(CO)₂]I^25,26 and forming new P–C bonds. The reaction of iridium complex [Cp*(PPh₃)(=PMes*)] with CH₂I₂ or CHI₃ yielded the related phosphenes.²⁷ The reaction of dinuclear Pt⁰ complex [Pt(dppe)(μ-PMes)]₂ with MeI afforded [Pt(dppe){μ-P(Me)Mes}]₂²⁺, which is classically nucleophilic and undergoes protonation, oxidation, and Lewis acid complexation.²⁸ In comparison to phosphinidene TM complexes, the phosphinidene complexes of main group elements are significantly less explored. Since the introduction of stable carbenes, they found a wide application to stabilize low valent compounds of main group elements including phosphinidene group.²⁹⁻³²

The syntheses and properties of phosphanylphosphinidene complexes of TM are one of the main research interests of our group. We have elaborated practical methods for accessing a variety of complexes with R₂P–P ligands using R₂P–P(SiMe₃)Li^{11,12,33−36} or using tBu₂P–P=PtBu₂(X) (X = Me or Br)¹⁷ as transport vehicles for the tBu₂P–P moiety. The reactivity of anionic W^VI complex [(DippN)₂(Cl)W(η²-tBu₂P–P)]⁻ was studied in more detail.¹¹ It was nucleophilic and reacted with electrophilic reagents, such as Ph₂PBr, PhPCl₂, or MeI, forming new P—P or P—C bonds.^34,35 However, the nucleophilicity of this complex is rather low. It yields adducts with Lewis acids such as MCl₃ (M = Al or Ga) or Cr(CO)₅·THF, but these reactions are clearly reversible.¹⁸ Chronologically, the first complexes reported with phosphanylphosphinidene ligands were [(R₃P)Pt⁰(η²-tBu₂P=P)].³⁷ They are strongly nucleophilic and differ significantly from phosphanylphosphinidene early TM complexes but their properties remain almost unexplored.²⁵ Herein, we report the reactions of [(DippN)₂W(Cl)(η²-P–PtBu₂)]⁻ (1), [(pTol₃P)₂Pt(η²-P=PtBu₂)] (2), and [(dppe)Pt(η²-P=PtBu₂)] (3) with electrophilic dihaloalkanes X(CH₂)_nX (n = 2–6, X = Br, I) to investigate the effect of carbon chain length on the products as well as advance the field of phosphanylphosphinidene chemistry.

2. Results and Discussion

The reactivity of phosphanylphosphinidene complex 1 toward dihaloalkanes was investigated (Scheme 2). The reaction of 1 with Br(CH₂)₃Br in a 1:1 molar ratio in DME is very clean and gave only tungsten complexes with tBu₂P–P(CH₂)₃Br (1b) as the ligand and LiX (X = Cl, Br) as main products (Scheme 2A). The ³¹P{¹H} NMR spectrum of the reaction mixture consists of only two pairs of doublets at 40.0/–125.3 ppm and at 36.9/–132.2 ppm, which can be attributed to complexes 1b-Cl and 1b-Br, respectively. These complexes differ only in the presence of chlorido (1b-Cl) or bromido ligands (1b-Br) directly bound to the tungsten atom. Moreover, the ¹J_PP coupling constants, with values of 375 Hz (1b-Cl) and 381 Hz (1b-Br), indicate that the P—P bond is retained in the newly formed ligand. Furthermore, the signals of 1b-Cl and 1b-Br in ³¹P{¹H} NMR spectra are accompanied by ¹J_PW satellites (¹J_P1W = 80 Hz), which confirm that the phosphorus ligand did not leave the coordination sphere of tungsten.

Scheme 2. Reactions of 1 with Dihaloalkanes.

A comparison of the ³¹P{¹H} NMR data of 1b-Cl/Br with the NMR data of parent compound 1 reveals that the doublets attributed to the P(CH₂)₃Br group in 1b-Cl/Br are strongly upfield shifted compared to those in 1 (−125.3/–132.2 ppm vs 17.7 ppm). Moreover, in the ³¹P{¹H} NMR spectra of 1b-Cl/Br these doublets split into doublets of triplets (²J_PH = 12 Hz). On the other hand, the ³¹P{¹H} NMR data of 1b-Cl/Br are similar to those observed for [(DippN)₂W(X)(1,2-η-tBu₂P–PCH₃)] (X= Cl, I) (1a) (44.1/–142.3 ppm and 33.7/–161.2 ppm, for the chloro- and iodo-derivatives, respectively), which were obtained previously by us.³⁵ Crystallization from a pentane solution gave yellow crystals in 48% yield, and the crystals contained 1b-Cl and 1b-Br in a 0.4:0.6 molar ratio according to the integrals of the ³¹P NMR signals. According to X-ray analysis the crystals were a solid solution of 1b-Cl and 1b-Br occupying the same positions (a kind of static disorder). Furthermore, we reacted 1 with 1,2-dibromoethane in a 1:1 molar ratio in DME, which led to a mixture of polyphosphorus compounds according to ³¹P{¹H} NMR analysis of the reaction solution. The only isolated product was [(ArN)₂WX₂(dme)] (X = Cl, Br),³⁸ and its structure was confirmed both by NMR spectroscopy and X-ray analysis. Therefore, we assume that the tBu₂P–P ligand leaves the coordination sphere of tungsten during this reaction.

The reactivity of 1 toward dihaloalkanes with longer aliphatic chains was also investigated. The progress of the reactions of 1 with Br(CH₂)_nBr (n = 4, 6) in a 1:1 molar ratio was monitored spectroscopically and revealed the formation of products with ³¹P{¹H} NMR spectra very similar to those of 1b-Cl/Br (see Table 1).

Table 1. ³¹P{¹H} NMR Data of Complexes 1b, 1c, and 1e.

	chemical shift [ppm]		coupling constant [Hz]
compound	(R-)P1	tBu2P2	1JP1P2	1JP1W	1JP2W
1b-Cl	–125.3	40.0	375	80	17
1b-Br	–132.2	36.9	381	80	17
1c-Cl	–122.2	40.3	378	76	17
1c-Br	–129.1	37.2	383	80	17
1e-Cl	–122.1	40.5	378	80	18
1e-Br	–129.0	37.4	382	80	18

A cursory analysis of the ³¹P{¹H} NMR spectra of the reaction mixtures would suggest the formation of a series of complexes analogous to 1b-Cl/Br. However, isolation of the products of these reactions in the crystalline form and X-ray structural analysis revealed the formation of dinuclear complexes (1c-Cl/Br, 1e-Cl/Br) with unusual tetradentate tBu₂P–P(CH₂)_nP–PtBu₂ ligands (Scheme 2B). As a result of halide exchange, these compounds were isolated as mixtures of isostructural chlorido and bromido complexes at a molar ratio of 1.3:0.7 according to the integrals of the ³¹P NMR signals. The bromido complexes can be easily converted into the corresponding chlorido complexes by the addition of three-fold excess of anhydrous LiCl in DME (Figure S17). In the case of the reaction involving 1,4-dibromobutane, the composition of the reaction mixture changes over time. The ³¹P{¹H} NMR spectrum of the reaction mixture after 0.5 h consists of only two sets of doublets, which can be attributed to 1c-Cl and 1c-Br. After prolonged stirring at room temperature, new resonances for 1d appeared (δ 42.3 ppm (d, tBu₂P); −37.3 (d, P (CH₂)₄); ¹J_PP = 203 Hz), and this was accompanied by a decrease in the intensities of the signals of 1c-Cl/Br. After 3 days, a high conversion of 1c-Cl/Br into 1d was observed. Furthermore, from this reaction mixture a significant amount of crystals of [(ArN)₂WX₂(dme)] (X = Cl, Br) was isolated. In the first stage of this reaction, dinuclear complexes 1c-Cl/Br are likely formed (Scheme 2C, n = 4). Next, 1c-Cl/Br reacts with the remaining Br(CH₂)₄Br, yielding diphosphane 1d consisting of a phospholane group and [(ArN)₂WX₂(dme)] (X = Cl, Br) (Scheme 2C). This type of reactivity is reminiscent of the reaction of nucleophilic phosphinidene zirconium complex [Cp₂Zr=PMes*(PMe₃)] with 1,2-dichloroxylene, which led to the formation of phospholane C₆H₄(CH₂)₂PMes*.²³ We did not observe the formation of the analogous diphosphanes with cyclic substituents from the reaction of equimolar amounts of 1 with Br(CH₂)_nBr (n = 3, 6). We suspect that the formation of 1d, containing a five-member phospholane ring, is thermodynamically favored. To verify this hypothesis, we calculated the ΔG° value for simplified ring-closing reactions: tBu₂P–P(H)(CH₂)_nBr → tBu₂P–P(CH₂)_n + HBr (n = 3–6) (see the SI for details). Indeed, the lowest and only negative value of ΔG° was found for reaction yielding 1d. Notably, reactions with a 2-fold excess of 1 relative to Br(CH₂)_nBr (n = 4, 6) gave the same dinuclear tungsten complexes as reactions with equimolar amounts of the substrates. Interestingly, the reaction of 1,3-dibromopropane even with excess 1 did not lead to a complex with tBu₂P–P(CH₂)₃P–PtBu₂ ligand. The space-filling model of 1c-Cl/Br, which contains four carbon atoms in the aliphatic chain linking the two P–PtBu₂ groups (Figure S2), reveals that this complex is very crowded. Therefore, the formation of analogous complexes with less than four carbon atoms in the aliphatic chain is not favored because of the steric effects of the bulky imido ligands.

The isolation of complexes 1b, 1c, and 1e in the crystalline form allowed us to discuss their solid-state structures in detail. The X-ray structures of 1b and 1c are presented in Figures 1 and 2, whereas the molecular structure of 1e is depicted in Figure S1. Complex 1b differs from complexes 1c and 1e in the number of metal centers and in the structure of the phosphorus ligands. In the solid-state structure of 1b, both phosphorus atoms of the tBu₂P–P(CH₂)₃Br ligand coordinate to the tungsten atom. Unlike 1b, where the propane chain is terminated by a bromine atom, in compounds 1c and 1e the aliphatic chain is terminated by a second tBu₂P–P group. The tetradentate tBu₂P–P(CH₂)_nP–PtBu₂ (n = 4, 6) ligands in 1c and 1e are side-on coordinated to two tungsten centers. Despite these differences, complexes 1b, 1c, and 1e exhibit many structural similarities. All the mentioned complexes feature pentacoordinated tungsten atoms. Furthermore, the P1—P2, P1—W1, and P2—W1 distances are very similar with values in ranges of 2.150(4)–2.168(2) Å, 2.506(1)–2.516(2) Å, and 2.540(2)–2.583(2) Å, respectively. The P1—P2 bonds in 1b, 1c, and 1e are longer than the corresponding distance in parent compound 1 (2.106(2) Å); however, they are still shorter than the sum of the single-bond covalent radii for P atoms (2.22 Å).³⁹ Furthermore, the P1—W1 bond distances in 1b, 1c, and 1e are significantly longer than that in 1 (2.406(1) Å), whereas the P2—W2 bond lengths are comparable to that observed in phosphanylphosphinidene complex 1 (2.571(1) Å). In comparison to 1b, 1c, and 1e, tungsten complexes possessing RP–PR′R″ ligand and PPW metallocycle such as [Cp(CO)₂W{P(tBu)−P(H)tBu}], and [Cp(CO)₂W{P(Cl)−P(Ph)N(SiMe₃)₂}] exhibit slightly longer P1—W1 distances (2.572(2)–2.576(3) Å) and significantly shorter P2—W1 bond lengths (2.335(2)–2.4209(9) Å).^40,41 Interestingly, all the P1 atoms show pyramidal geometries (sum of angles ΣP1 284.1–291.9°), and the P2 atoms are all tetrahedral; however, neglecting the P2—W1 bond, the tBu₂P phosphanyl groups exhibit a high degree of planarity (ΣP2 338.5°–341.7°). The torsion angles of (CH₂)C1—P1—P2—C4(tBu) are in the range from −17.0(6)° to 12.8(3)° and indicate the syn-periplanar orientation of the tBu group and the CH₂ moiety directly bound to the P1 atom; moreover, it points to the presence of a lone pair of electrons on the P1 atom. The analogous ligand geometry was previously observed by us for the methylated phosphanylphosphinidene group in [(DippN)₂W(X)(1,2-η-tBu₂P–PCH₃)] (X = Cl, I) (1a).³⁵

Figure 1.

Molecular structure of complex 1b. Displacement ellipsoids are shown at 50% probability. H atoms are omitted for clarity. Selected bond lengths (Å) and angles (°): P1—W1 2.508(2), P2—W1 2.583(2), P1—P2 2.155(2), C1—P1 1.869(4), ΣP1 291.9, ΣP2 338.5 (neglecting the P2—W1 bond), C1—P1—P2 113.4(2), C1—P1—P2—C4 7.8(3).

Figure 2.

Molecular structure of complex 1c. Ellipsoids are shown at 50% probability. H atoms are omitted for clarity. Selected bond lengths (Å) and angles (°): P1—W1 2.506(1), P2—W1 2.580(2), P1—P2 2.168(2), C1—P1 1.874(5), ΣP1 284.6, ΣP2 340.4 (neglecting the P2—W1 bond), C1—P1—P2 110.3(2), C1—P1—P2—C7 12.8(3). Atoms labeled with primes are related by symmetry code (1-x, 1-y, 1-z), i.e., symmetry center.

In the second part of our study, we investigated the reactivity of platinum phosphanylphosphinidene complexes 2 and 3 toward haloalkanes. The methylation of 2 and 3 by MeI afforded complexes 2a and 3a, respectively, bearing tBu₂P–PMe ligands (Scheme 3). In the case of the reaction of 2 with MeI, strong signals of free pTol₃P and resonances of 2a were observed in the ³¹P{¹H} NMR spectra of the reaction mixture. This suggests a replacement of pTol₃P with an iodido ligand in the coordination sphere of platinum. Because of the chelating nature of dppe, such ligand exchange was not observed in the reaction involving 3, and only cationic complex 3a was formed. Complex 2a was isolated in its crystalline form from a toluene solution at low temperature in 49% yield. Because of its ionic character, 3a exhibits lower solubility in hydrocarbons and was obtained from a THF solution at low temperature in 60% yield.

Scheme 3. Reactions of 2 and 3 with MeI.

The reactivities of 2 and 3 toward I(CH₂)₂I differ significantly. According to the ³¹P{¹H} NMR spectra of the reaction mixtures, the reaction of 2 with I(CH₂)₂I gave solely new platinum complex 2b bearing a tBu₂P–P–I ligand together with pTol₃P (Scheme 4A). Moreover, in the ¹H NMR spectrum of this reaction mixture, a resonance at 5.25 ppm attributed to ethylene is present. Complex 2b was isolated from a toluene solution at low temperature as brownish crystals in 50% yield. Otherwise, the reaction of 3 with I(CH₂)₂I did not yield the analogous platinum complex. The tBu₂P–P group was lost from the Pt center, and the P—P bond within this ligand was cleaved, resulting in the formation of tBu₂PI, insoluble orange phosphorus polymers, [(dppe)PtI₂] (3b)⁴² and C₂H₄ (Scheme 4B).

Scheme 4. Reactions of 2 and 3 with X(CH₂)₂X (X = Br or I).

Surprisingly, the reaction of 3 with Br(CH₂)₂Br led to the formation of dimeric platinum complex 3c (Scheme 4C). This complex features a high-order ³¹P{¹H} NMR spectrum with four multiplets at 67.9 ppm (t-Bu₂P), 50.1 ppm (dppe), 47.1 ppm (dppe), and 120.1 ppm (P) (spin system AA′LL′MM′XX′). This suggests the formation of a tBu₂PPPPtBu₂ ligand in the coordination sphere of platinum. Complex 3c exhibits very low solubility in hydrocarbons, but it is highly soluble in dichloromethane (DCM). Crystallization from this solvent layered with toluene at room temperature gave large light-green crystals of 3c in 27% yield. The reaction of 2 with Br(CH₂)₂Br also gave products with high-order spectra (66.0 ppm (t-Bu₂P), 23.3 ppm (pTol₃P), −71.5 ppm (P); AA′MM′XX′ spin system) together with a strong resonance from free pTol₃P and other minor unidentified products. This suggests the formation of the same tBu₂PPPPtBu₂ ligand, which coordinates to two Pt(pTol₃P)Br fragments. However, unlike 3b, this platinum complex is highly soluble in hydrocarbons, and we were not able to obtain X-ray-quality crystals of this product.

In contrast to reactions of 1 with Br(CH₂)_nBr (n = 3, 4, 6), the analogous reactions involving 2 and 3 gave mostly oily products that were difficult to isolate and characterize. Despite this fact, we were able to obtain crystals of complex 2c from the reaction of 2 with an equimolar amount of Br(CH₂)₆Br (Scheme 5). The structure of 2c was unambiguously characterized by both NMR spectroscopy and single-crystal X-ray diffraction. ³¹P{¹H} NMR spectroscopy showed that the aforementioned reaction is very clean, where 2c and free pTol₃P are the only products.

Scheme 5. Reactions of 2 with Br(CH₂)₆Br.

The ³¹P{¹H} NMR data of complexes 2a–c, 3a, and 3c, together with corresponding data of parent compounds 2 and 3, are collected in Table 2.

Table 2. ³¹P{¹H} NMR Data of 2, 3, 2a–c, 3a, and 3c.

	chemical shifts [ppm]				coupling constants [Hz]
compound	(R-)P1	tBu2P2	R′3P3	R′3P4	1JP1P22JP1P32JP1P4	2JP2P32JP2P42JP3P4	1JP1Pt1JP2Pt1JP3Pt1JP4Pt
2	–38.8	77.5	30.5	22.5	615	206	52
					2	34	1906
					21	4	3452
							3397
3	–48.2	71.5	58.3	42.6	622	214	116
					12	31	1894
					26	11	3358
							2915
2a	–97.7	61.2	22.3		483	295	349
					8		1653
							3623
2b	–30.6	64.2	21.5		520	299	170
					6		1598
							3523
2c	–68.0	54.8	23.4		483	299	432
					8		1694
							3606
3a	–130.8	54.5	51.2	49.9	455	230	290
					36	24	1710
					71		2990
							2774
3c	–120.1	67.9	50.1	47.1			416
							1696
							3052
							2854

The comparison of the ³¹P{¹H} NMR data of platinum complexes with tBu₂P2–P1–R (R = Me, I, (CH₂)₆Br, P–PtBu₂) ligands with those of parent compounds 2 and 3 leads to several interesting observations. The ³¹P{¹H} spectra of 2a, 2b, and 2c show only three resonances each, which suggests that one phosphine ligand left the coordination sphere of the metal center. On the other hand, the ³¹P{¹H} NMR spectra of 3a and 3c each contain four resonances, indicating the presence of four inequivalent P atoms in these compounds. In comparison to parent species 2 and 3, the resonances of P1–R in the aforementioned complexes, except 2b, which contains a P—I moiety, are strongly upfield shifted, indicating the formation of new P—C (in 2a, 2c, and 3a) or P—P bonds (3c). In contrast, the resonances of tBu₂P2 groups in the newly formed Pt complexes are comparable to those observed in parent species 2 and 3. A strong correlation between ¹J_P1P2 and P—P bond length is observed for phosphanylphosphinidene transition metal complexes.¹⁸ Two extreme examples are side-on platinum complex 2 (large ¹J_P1P2 = 615 Hz and very short P—P bond distance with value of 2.062(2) Å)¹² and terminal zirconium complex [Cp₂Zr(PPhMe₂)(η¹-P–PtBu₂)] (small ¹J_P1P2 = 284 Hz and very long P—P bond distance with a value of 2.20(4) Å).³³ The absolute values of ¹J_P1P2 in 2a–c and 3a are significantly decreased in comparison to those of 2 and 3, which suggests elongation of the P—P bond within the ligand. Notably, all resonances for P atoms in 2a–c, 3a, and 3c showed platinum satellites.

The small absolute values of ¹J_P1Pt, which are very characteristic of phosphanylphosphinidene complexes 2 and 3, are significantly increased in the newly formed compounds. Furthermore, the ¹J_P2Pt, ¹J_P3Pt, or ¹J_P4Pt coupling constants are similar to the corresponding values observed for 2, 3, [trans-(R₃P)₂PtCl₂],⁴³ and Pt(0) complexes with phosphine ligands.⁴⁴ The relatively large absolute value of the ²J_P2P3 couplings (295–299 Hz) in 2a–c suggests the trans orientation of the tBu₂P1 moiety and the pTol₃P3 ligand.

The solid-state structures of platinum complexes 2a, 2b, 2c, 3a, and 3c were studied by X-ray diffraction. The molecular structures of these compounds are shown in Figures 3–7. The X-ray studies of 2a, 2b, 2c, 3a, and 3c in solution are fully consistent with the NMR data of these complexes. In 2a, 2b, 2c, and 3a, the tBu₂P–P–R moiety (R = Me (2a, 3a), I (2b), (CH₂)₆Br (2c)) is side-on coordinated to the Pt center (Figures 3–6), and the metal atom is tetracoordinated with a planar geometry. In 2a–c, in accordance with the ³¹P NMR data, the pTol₃P ligand and tBu₂P are in a trans orientation. Surprisingly, the geometries of the tBu₂P–P–R ligands in 2a–c and 3a resemble those observed for tungsten complexes 1a–e: (i) the tBu₂P group displays a high degree of planarity (ΣP2: 345.4° to 347.2°); (ii) the P—P bonds have lengths in between the lengths typical of single and double bonds (2.149(3) Å to 2.173(1) Å) and are significantly longer than P—P bonds in precursor complexes 2 (2.062(2) Å)¹² and 3 (2.072(3) Å);¹³ (iii) the angles P2—P1—R have values in a narrow range of 108.6(2)° to 110.1(3)°; (iv) one of the tBu groups is syn-periplanar with respect to the R group with torsion angles for C(tBu)–P2—P1—R from −12.5(5)° to 8.3(4)°.

Figure 3.

Molecular structure of complex 2a. Ellipsoids are shown at 50% probability. H atoms are omitted for clarity. Selected bond lengths (Å) and angles (°): P1—Pt1 2.350(2), P2—Pt1 2.285(1), P3—Pt1 2.292(1), I1—Pt1 2.6658(5), P1—P2 2.156(2), C1—P1 1.863(6), ΣP1 278.2, ΣP2 347.1 (neglecting the P2—Pt1 bond), C1—P1—P2 108.6(2), C1—P1—P2—C6 −10.3(3).

Figure 7.

Molecular structure of complex dication 3c. Ellipsoids are shown at 50% probability. H atoms and bromide anions are omitted for clarity. Selected bond lengths (Å) and angles (°): P1—Pt1 2.415(1), P2—Pt1 2.287(1), P3—Pt1 2.304(1), P4—Pt1 2.275(1), P1—P2 2.165(1), P1—P1′ 2.235(1), ΣP1 277.8, ΣP2 346.8 (neglecting the P2—Pt1 bond), P2—P1—P1′ 106.34(5), P2—P1—P1′—P2′ 180 (centrosymmetric structure).

Figure 6.

Molecular structure of complex cation 3a. One molecule out of the three present in the asymmetric unit was selected. Ellipsoids are shown at 50% probability. H atoms, solvent molecules, and iodide anion are omitted for clarity. Selected bond lengths (Å) and angles (°): P1—Pt1 2.406(2), P2—Pt1 2.285(2), P3—Pt1 2.274(2), P4—Pt1 2.274(2), P1—P2 2.157(3), C100—P1 1.862(8), ΣP1 278.5, ΣP2 345.4 (neglecting the P2—Pt1 bond), C100—P1—P2 108.6(2), C100—P1—P2–C62 8.3(4).

Figure 4.

Molecular structure of complex 2b. Ellipsoids are shown at 50% probability. H atoms are omitted for clarity. Selected bond lengths (Å) and angles (°): P1—Pt1 2.310(1), P2—Pt1 2.282(1), P3—Pt1 2.3004(9), I1—Pt1 2.6551(5), P1—P2 2.173(1), I2—P1 2.491(1), ΣP1 280.4, ΣP2 347.2 (neglecting the P2—Pt1 bond), I2—P1—P2 109.57(5), I2—P1—P2—C1 −7.9(2).

Figure 5.

Molecular structure of complex 2c. Ellipsoids are shown at 50% probability. H atoms are omitted for clarity. Selected bond lengths (Å) and angles (°): P1—Pt1 2.322(3), P2—Pt1 2.282(2), P3—Pt1 2.283(2), Br1—Pt1 2.519(1), P1—P2 2.149(3), C9—P1 1.87(1), ΣP1 278.0, ΣP2 347.2 (neglecting the P2—Pt1 bond), C9—P1—P2 109.6(3), C9—P1—P2—C5 −12.5(5).

Unlike tungsten complexes 1a–c and 1e, in the aforementioned platinum complexes significant elongation of the P1—M1 bond resulting from the attachment of the R group to the P1 atom was not observed. The P1—Pt1 distances in 2a–c (2.310(1) Å to 2.350(2) Å) are even shorter than that in parent species 2 (2.409(2) Å), whereas in 3a, the P1—Pt1 bond length (2.406(2) Å) is very similar to the corresponding distance in 3 (2.387(2) Å). The P2—Pt1, P3—Pt1, and P4—Pt1 distances are comparable to those observed in platinum complexes with phosphine ligands.⁴⁵

The molecular structure of complex dication 3c is presented in Figure 7. It consists of tetraphosphorus ligand tBu₂P2—P1—P1′—P2′tBu₂ and two dppe ligands that coordinate to two platinum centers. Additionally, two bromide counterions are present in the second coordination sphere (not shown in Figure 7).

The metal centers show square planar geometries and the whole molecule is centrosymmetric (point group C_i). As a consequence, the P2—P1—P1′—P2′ bonds lie in the same plane with a corresponding torsion angle of 180° and the two (dppe)Pt moieties are located on opposite sides of this plane. The P1—P1′ bond (2.235(1) Å) has a length typical of a single covalent P—P bond, whereas the P2—P1 and P2′—P1′ bonds are 0.07 Å shorter. The platinum—phosphorus bonds in 3c and in parent complex 3 have very similar lengths. Dimeric molybdenum and tungsten complexes with analogous tBu₂PPPPtBu₂ ligands were previously synthesized by our group from the reaction of Li[Cp*(CO)₃] with tBu₂P–PCl₂.⁴⁶ The tetraphosphorus ligands in these complexes displayed geometries very similar to the corresponding ligand in 3c.

We performed DFT calculations (see SI for details) to further elucidate the electronic structures of the obtained tungsten and platinum complexes. As presented in the previous paragraphs, W or Pt complexes with tBu₂P–P–R exhibit many common structural features. Therefore, for this study we selected representative complexes 1a, 2a (tBu₂P–P–Me ligand), and 2b (tBu₂P–P–I ligand). Moreover, we studied the electronic properties of complex 3c′ (tBu₂P–P–P–PtBu₂ ligand) with a skeleton similar to that of 3c in which the dppe ligands were replaced by dmpe (Me₂PCH₂CH₂PMe₂) groups to simplify the calculations. Our previous theoretical studies on tungsten complex 1 revealed that the P1—P2 bond within the tBu₂P2–P1 ligand is polarized toward the phosphinidene P1-atom. Furthermore, the P1—P2 and P2—W1 bonds are essentially single bonds, whereas the P1—W1 bond has double bond character. Moreover, a lone electron pair is present on the P1 atom. In the case of Pt complex 2, similar to 1, the phosphanylphosphinidene ligand displays a positively charged P2 atom and a negatively charged P1 atom. In contrast to 1, Pt complex 2 exhibits a P1=P2 double bond and has two lone pairs on the P1 atom.¹⁸ NBO analysis of complexes 1a, 2a, and 2b indicates that the P1—P2 bond within the tBu₂P–P–R ligand as well as the P1—M1 and P2—M1 bonds have single-bond character. The mentioned complexes display one lone pair of electrons on the P1 atom. The shortening of the P1—P2 bonds in 1a, 2a, and 2b can be explained by the interactions of the antibonding σ*(P2–C) orbitals with the orbital attributed to the lone pair on the P1 atom (negative hyperconjugation). The analysis of the Hirshfeld charges of complexes 1a, 2a, and 2b revealed that the positive charge is located on the P2 atom of the phosphanyl group, whereas the charge on the P1 atom is close to zero (Table 3). Moreover, the W1 atom in 1a is positively charged, whereas the charges on the Pt1 atoms in 2a and 2b are close to zero. As it can be expected, in the case of 1a significant negative charges are located on imido and chlorido ligands, as well as methyl group bound to P1 atom (Figure S72). In complexes 2a and 2b, negative charge is located primarily on iodido ligands and on the methyl group (2a) or iodine atom (2b) directly bound to P1 atom (Figures S73 and S74). These results indicate that the phosphorus ligands in 1a, 2a, and 2b can be seen as coordinated diphosphenium cations tBu₂P⁺=P–R resulting formally from the reaction of the tBu₂P–P group with the R⁺ cation. A similar bonding mode is observed in complex 3c, where dicationic tBu₂P⁺=P–P=P⁺tBu₂ ligand coordinates to two platinum metal centers. Notably, based on our previous calculations, the phosphorus ligands in dimeric complexes [Cp*M(CO)₃(η²-tBu₂PP)]₂ (M = Mo, W) possess analogous Lewis structures.⁴⁶

Table 3. Calculated Hirshfeld Charges (q) and Wiberg Bond Indexes for Complexes 1a, 2a, 2b, and 3c.

	Hirshfeld charges			Wiberg bond indexes
compound	q(P2)	q(P1)	q(M1)	P1—P2	P1—P1′	P1—M	P2—M
1a	0.194	0.057	0.431	1.002		0.727	0.511
2a	0.208	0.033	0.030	1.116		0.510	0.490
2b	0.205	0.004	0.043	1.093		0.556	0.479
3c′	0.193	–0.023	0.035	1.089	0.983	0.412	0.461

Consequently, we performed analogous calculations for free phosphenium cations tBu₂P⁺=P–Me (I),tBu₂P⁺=P–I (II) and (tBu₂P⁺=P)₂ (III). On the basis of our calculations, these species have a singlet ground state. The optimized structures of I–III are presented in Figures S66, S70, and S71, and their selected optimized parameters together with Hirshfeld charges are collected in Table 4.

Table 4. Calculated Hirshfeld Charges (q) and Optimized Parameters for Free Phosphenium Cations I–III^a.

cation	q(P2)	q(P1)	P1—P2 (Å)	P1—P1′ (Å)	ΣP2 (°)	P2—P1—R (°)
tBu2P+=P-Me(I)	0.304	0.220	2.036		359.3	107.4
			(1a: 2.160) (2a: 2.156)		(1a: 341.7) (2a: 347.1)	(1a: 109.9) (2a: 108.6)
tBu2P+=P—I(II)	0.294	0.168	2.055		359.3	109.0
			(2b: 2.173)		(2b: 347.2)	(2b: 109.6)
(tBu2P+=P)2(III)	0.345	0.140	2.057	2.224	359.9	102.4
			(3c: 2.165)	(3c: 2.235)	(3c: 346.8)	(3c: 106.3)

^aValues in parentheses are experimental parameters for the corresponding ligands in 1a, 2a, 2b, and 3c.

As expected, the P atoms in I-III are positively charged with a large charge on the P2 atom and a smaller positive charge on the P1 atom. A comparison of the geometries of I-III with the geometries of the corresponding ligands in 1a, 2a, 2b, and 2c reveals several similarities, such as the planar geometric alignment of the tBu₂P2 phosphanyl group, the very close values of the P2—P1—R angles, and the same syn-periplanar conformation (Table 4). Similar structural features also include the isolated, noncoordinated diphosphenium cation Mes*(Me)P⁺=PMes*.⁴⁷ However, in comparison to the corresponding ligands in the W and Pt complexes, the P1—P2 bonds in I–III are significantly shorter and have double bond character. This important structural difference can be explained by considering the complexation of these cationic ligands to the metal center. In free ligands I–III, the lone pair on the P2 atom (tBu₂P group) is mainly involved in P—P π-bonding, whereas in the corresponding complexes, this lone pair interacts with the metal center.

3. Conclusions

Our studies showed that phosphanylphosphinidene complexes of tungsten and platinum are valuable substrates in the synthesis of not only new diphosphorus ligand species but also new polydentate phosphorus ligands. The reactions of complexes [(DippN)₂W(Cl)(η²-P–PtBu₂)]⁻ (1), [(pTol₃P)₂Pt(η²-P=PtBu₂)] (2), and [(dppe)Pt(η²-P=PtBu₂)] (3) with MeI and haloalkanes gave a wide range of transition metal complexes bearing ligands with two or four P-donor atoms. Nucleophilic 1 is very reactive toward Br(CH₂)_nBr (n = 3, 4, 6), forming unprecedented dinuclear complexes bearing tetradentate ligands where two tBu₂P–P groups are linked by an aliphatic chain (n = 4, 6) or monometallic complexes with a tBu₂P–P(CH₂)₃Br ligand. The reactions of platinum complexes with MeI and dihaloalkanes gave even more diverse compounds. We showed that the tBu₂P–P ligand in the starting platinum complexes can be easily functionalized by introducing a wide range of substituents on terminal P-phosphinidene atoms, such as halogen atoms, Me, (CH₂)_nBr or P–PtBu₂ groups. Despite the diversity of functionalized phosphanylphosphinidene ligands, they exhibit many structural similarities and can be described as phosphenium cations tBu₂P⁺=P − R or (tBu₂P⁺=P)₂. In summary, the presented results may be of importance in the synthesis of polydentate phosphorus ligands coordinated to TM with possible catalytic activity.

4. Experimental Section

General Information

All experiments were carried out under an argon atmosphere using Schlenk techniques. All manipulations were performed using standard vacuum, Schlenk, and glovebox techniques. All solvents were purified and dried using common methods. Solvents for NMR spectroscopy (C₆D₆ and CDCl₃) were purified from metallic sodium or P₂O₅. The phosphanylphosphinidene tungsten complex [(2,6-iPr₂C₆H₃N)₂(Cl)W(η²-tBu₂P–P)]Li·3DME (1)¹¹ and phosphanylphosphinidene platinum complex [(pTol₃P)₂Pt(η²-tBu₂P=P)] (2)¹² were synthesized following literature methods. Methyl iodide, 1,2-diiodoethane, 1,2-dibromoethane, 1,3-dibromopropane, 1,4-dibromobutane and 1,6-dibromohexane were purchased from commercial sources. All of the solutions of dibromoalkanes, methyl iodide, and 1,2-diiodoethane used in this work were freshly prepared prior to use. NMR spectra were recorded on a Bruker Avance III HD 400 MHz spectrometer at ambient temperature (external standards: TMS for ¹H and ¹³C; 85% H₃PO₄ for ³¹P). The chemical shifts of C_i and CH₂ in some cases were not determined due to the absence of these signals in the ¹³C{¹H} NMR spectra. The Cl/Br ratio in the case of tungsten complexes was determined on the basis of the ³¹P NMR spectra. Crystallographic analyses were performed on an STOE IPDS II diffractometer using MoKα radiation (λ = 0.71073 Å). Elemental analyses were performed at the University of Gdańsk using a Vario El Cube CHNS apparatus.

Synthesis of 1b

To a solution of 1 (0.512 g, 0.500 mmol) in 4 mL of DME was dropwise added 0.873 mL of a solution of 1,3-dibromopropane (0.500 mmol, C_M = 0.573 M) at −30 °C. After warming to room temperature, NMR spectra were collected every 5 min for 30 min. The reaction was complete after this time. The solvent was evaporated, the solid residue was redissolved in pentane, and the LiBr precipitate was removed by filtration. Yellow crystals of 1b-Cl/1b-Br (0.213 g, 0.240 mmol, yield 48%, molar ratio 1b-Cl/1b-Br equals 0.6:0.4 on the basis of the ³¹P NMR spectrum) were obtained from the pentane filtrate at −30 °C. Mixing in C₆D₆ or DME and heating overnight at 50 °C did not result in the formation of a compound analogous to 1d.

NMR data for 1b:

¹H NMR (C₆D₆, 400 MHz, 298 K δ): 1.22 (broad s, 12H, HC(CH₃)₂), 1.27 (d, ³J_HH = 7 Hz, 6H, HC(CH₃)₂), 1.28 (d, ³J_HH = 7 Hz, 6H, HC(CH₃)₂), 1.35 (d, ³J_PH = 16 Hz, 18H, C(CH₃)₃), 1.82 (m, 2H, PCH₂), 2.44 (m, 2H, CH₂), 2.89 (m, 2H, CH₂Br), 4.09 (m, 4H, HC(CH₃)₂), 6.97 (m, 2H, C_Ar–H_p), 7.07 (m, overlapped, 4H, C_Ar–H_m).

1b-Cl: ³¹P{¹H} NMR (C₆D₆, 162 MHz, 298 K, δ): 40.0 (d, ¹J_PP = 375 Hz, ¹J_PW = 17 Hz, tBu₂P), −125.3 (d, ¹J_PP = 375 Hz, ¹J_PW = 80 Hz, P(CH₂)₃Br).

1b-Br: ³¹P{¹H} NMR (C₆D₆, 162 MHz, 298 K, δ): 36.9 (d, ¹J_PP = 381 Hz, ¹J_PW = 17 Hz, tBu₂P), −132.2 (d, ¹J_PP = 381 Hz, ¹J_PW = 80 Hz, P(CH₂)₃Br).

¹³C{¹H} NMR (C₆D₆, 100 MHz, 298 K δ): 22.8 (dd, ¹J_CP= 44 Hz, ²J_CP= 4 Hz, PCH₂), 23.7 (broad s, HC(CH₃)₂), 23.8 (broad s, HC(CH₃)₂), 24.1 (broad s, HC(CH₃)₂), 27.9 (m, HC(CH₃)₂), 31.6 (broad s, C(CH₃)₃), 32.8 (m, CH₂), 35.1 (m, BrCH₂), 37.6 (very broad s, C(CH₃)₃), 122.4 (s, C_m), 122.5 (s, C_m), 125.8 (broad s, C_p), 144.3 (m, overlapped, C_o), 152.3 (m, overlapped, C_i).

Elemental analysis calculated for C₃₅H₅₈Br_1.4Cl_0.6N₂P₂W (M = 885.77 g/mol): % C = 47.46%, % H = 6.60%, % N = 3.16%; found % C = 47.55%, % H = 6.70%, % N = 3.15%.

Synthesis of 1c

To a solution of 1 (0.506 g, 0.494 mmol) in 4 mL of DME was dropwise added 1.29 mL of a solution of 1,4-dibromobutane (0.494 mmol, C_M = 0.383 M) at −30 °C. After warming to room temperature, NMR spectra were collected every 5 min for 30 min. The solvent was evaporated, the solid residue was redissolved in pentane, and the LiBr precipitate was removed by filtration. Yellow crystals of 1c-Cl/1c-Br (0.133 g, 0.084 mmol, yield 34.1%, molar ratio 1c-Cl/1c-Br equals 1.3:0.7 on the basis of the ³¹P NMR spectrum) were obtained from the pentane filtrate at −30 °C. Crystals for NMR spectroscopy and elemental analysis were obtained from a toluene solution at −30 °C, and the crystals contain two molecules of toluene in the structure.

NMR data for 1c:

¹H NMR (C₆D₆, 400 MHz, 298 K δ): 1.23 (very broad s, overlapped, 24H, HC(CH₃)₂), 1.28 (d, overlapped, ³J_HH = 7 Hz, 24H, HC(CH₃)₂), 1.38 (d, ³J_PH = 16 Hz, 36H, C(CH₃)₃), 1.55 (broad m, 4H, PCH₂), 2.32 (m, 4H, CH₂), 4.11 (very broad s, 8H, HC(CH₃)₂), 6.98 (m, 4H, C_Ar–H_p), 7.07 (m, overlapped, 8H, C_Ar–H_m).

1c-Cl: ³¹P{¹H} NMR (C₆D₆, 162 MHz, 298 K, δ): 40.3 (d, ¹J_PP = 378 Hz, ¹J_PW = 17 Hz, tBu₂P), −122.2 (d, ¹J_PP = 378 Hz, ¹J_PW = 76 Hz, P(CH₂)₄).

1c-Br: ³¹P{¹H} NMR (C₆D₆, 162 MHz, 298 K, δ): 37.2 (d, ¹J_PP = 383 Hz, ¹J_PW = 17 Hz, tBu₂P), −129.1 (d, ¹J_PP = 383 Hz, ¹J_PW = 80 Hz, P(CH₂)₄).

¹³C{¹H} NMR (C₆D₆, 100 MHz, 298 K δ): 23.7 (broad s, HC(CH₃)₂), 23.8 (broad s, HC(CH₃)₂), 24.2 (broad s, HC(CH₃)₂), 27.8 (m, overlapped, HC(CH₃)₂), 31.6 (broad s, (C(CH₃)₃), 37.4 (broad s, C(CH₃)₃), 122.4 (s, C_m), 122.5 (s, C_m), 125.7 (broad s, C_p), 144.2 (m, overlapped, C_o), 152.3 (m, overlapped, C_i), CH₂– are not visible due to the broadness.

Elemental analysis calculated for C₈₂H₁₂₈Br_0.5Cl_1.5N₄P₄W₂ (M = 1754.63 g/mol): % C = 56.13%, % H = 7.35%, % N = 3.19%; found % C = 56.03%, % H = 7.26%, % N = 3.18%.

Synthesis of 1d

The reaction was conducted using the same amounts of reactants as were used to synthesize 1c-Cl/1c-Br at room temperature, and after 3 days almost all 1c-Cl/1c-Br was gone and 1d was formed along with [(2,6-iPr₂C₆H₃N)₂WX₂·DME (X = Cl, Br). The molar ratio of the products (1d/1c) was 2.3:1 based on the ³¹P{¹H} NMR spectrum (70% 1d and 30% 1c-Cl/1c-Br, not taking into account other products of this reaction).

NMR data for 1d:

¹H NMR (C₆D₆, 400 MHz, 298 K δ): 1.24 (d, ³J_PH = 7 Hz, 18H, C(CH₃)₃), 1.54 (m, 4H, CH₂), 1.77 (m, 4H, CH₂).

³¹P{¹H} NMR (C₆D₆, 162 MHz, 298 K, δ): δ 42.3 (d, ¹J_PP = 203 Hz, tBu₂P), −37.3 (d, ¹J_PP = 203 Hz, P(CH₂)₄).

¹³C{¹H} NMR (C₆D₆, 100 MHz, 298 K δ): 26.2 (dd, ¹J_CP = 18 Hz, ²J_CP = 13 Hz, PCH₂), 28.6 (broad s, CH₂), 31.6 (broad s, (C(CH₃)₃), 32.8 (dd, ¹J_CP = 30 Hz, ²J_CP = 7 Hz, C(CH₃)₃).

Synthesis of 1e

To a solution of 1 (0.493 g, 0.480 mmol) in DME was dropwise added 1.68 mL of a solution of 1,6-dibromohexane (0.480 mmol, C_M = 0.286 M) at −30 °C. After warming to room temperature, NMR spectra were collected every 5 min for 30 min. The solvent was evaporated, and the solid residue was redissolved in pentane. Colorless crystals of 1e-Cl/1e-Br (0.162 g, 0.101 mmol, yield 42%, molar ratio 1e-Cl/1e-Br equals 1.3:0.7 on the basis of the ³¹P NMR spectrum) were grown at −30 °C. Adding the reactants in the reverse manner results in the same NMR spectra and crystalline product. No formation of a compound analogous to 1d was observed at RT.

NMR data for 1e:

¹H NMR (C₆D₆, 400 MHz, 298 K δ): 0.99 (broad m, overlapped, 4H, PCH₂), 1.25 (broad s, overlapped, 4H, CH₂), 1.25 (very broad s, 18H, HC(CH₃)₂), 1.30 (d, overlapped, 30H, ³J_HH = 7 Hz, HC(CH₃)₂), 1.40 (d, 36H, ³J_PH = 16 Hz, C(CH₃)₃), 2.38 (m, 4H, CH₂), 4.14 (m, 8H, HC(CH₃)₂), 6.97 (m, 4H, C_Ar–H_p), 7.08 (m, overlapped, 8H, C_Ar–H_m).

1e-Cl: ³¹P{¹H} NMR (C₆D₆, 162 MHz, 298 K, δ): 40.5 (d, ¹J_PP = 378 Hz, ¹J_PW = 18 Hz, tBu₂P), −122.1 (d, ¹J_PP = 378 Hz, ¹J_PW = 80 Hz, P(CH₂)₆).

1e-Br: ³¹P{¹H} NMR (C₆D₆, 162 MHz, 298 K, δ): 37.4 (d, ¹J_PP = 382 Hz, ¹J_PW = 18 Hz, tBu₂P), −129.0 (d, ¹J_PP = 382 Hz, ¹J_PW = 80 Hz, P(CH₂)₆).

¹³C{¹H} NMR (C₆D₆, 100 MHz, 298 K δ): 23.8 (broad s, HC(CH₃)₂), 23.9 (broad s, HC(CH₃)₂), 24.2 (broad s, HC(CH₃)₂), 24.2 (dd, ¹J_CP = 44 Hz, ²J_CP = 6 Hz, PCH₂), 27.8 (s, overlapped, HC(CH₃)₂), 27.9 (s, overlapped, HC(CH₃)₂), 30.4 (m, CH₂), 31.7 (broad s, C(CH₃)₃), 32.7 (m, CH₂), 37.5 (broad s, C(CH₃)₃), 122.4 (s, C_m), 122.5 (s, C_m), 125.7 (broad s, C_p), 144.4 (m, overlapped, C_o), 152.5 (m, overlapped, C_i).

Additionally, the signals attributable to pentane are visible in the ¹H and ¹³C{¹H} NMR spectra.

Elemental analysis calculated for (1e·pentane): C₇₅H₁₂₈Br_0.7Cl_1.3N₄P₄W₂ (M = 1679.44 g/mol): % C = 53.64%, % H = 7.68%, % N = 3.34%; found % C = 53.41%, % H = 7.80%, % N = 3.13%.

Synthesis of 2a

To a suspension of 2 (0.379 g, 0.383 mmol) in toluene was dropwise added 0.586 mL of a solution of methyl iodide (0.383 mmol, C_M = 0.653 M) at −30 °C. The reaction was complete after 1 h, which was confirmed by NMR spectroscopy. The solvent was evaporated, and the solid residue was dissolved partially in pentane and the rest in toluene. Colorless crystals of 2a were obtained from both fractions at −30 °C but they were contaminated with pTol₃P (the crystals obtained from toluene were much less contaminated than those from pentane). The yield of crystals from the toluene fraction was 49.2% (0.154 g, 0.188 mmol).

NMR data for 2a:

¹H NMR (C₆D₆, 400 MHz, 298 K δ): 0.73 (m, 3H, H₃C–P), 1.35 (d, ³J_PH = 16 Hz, 9H, C(CH₃)₃), 1.37 (d, ³J_PH = 16 Hz, 9H, C(CH₃)₃), 1.93 (s, 9H, p-CH₃-C₆H₄), 6.90 (d, ³J_HH = 7 Hz, 6H, C_Ar–H_m), 7.80 (m, 6H, C_Ar–H_o).

³¹P{¹H} NMR (C₆D₆, 162 MHz, 298 K, δ): 61.2 (dd, ¹J_PP = 483 Hz, ²J_PP = 295 Hz, ¹J_PPt = 1653 Hz, tBu₂P), 22.3 (dd, ²J_PP = 295 Hz, ²J_PP = 8 Hz, ¹J_PPt = 3623, pTol₃P), −97.7 (dd, ¹J_PP = 483 Hz, ²J_PP = 8 Hz, ¹J_PPt = 349 Hz, PMe), weak signal of pTol₃P (s, −7.9 ppm) was visible.

¹³C{¹H} NMR (C₆D₆, 100 MHz, 298 K δ): 3.7 (dd, ¹J_CP = 55 Hz, ²J_CP = 7 Hz, H₃C-P), 20.8 (s, p-CH₃–C₆H₄), 31.8 (d, ²J_CP = 8 Hz, C(CH₃)₃), 32.2 (m, C(CH₃)₃), 36.1 (m, C(CH₃)₃), 37.2 (m, C(CH₃)₃), 128.9 (d, ³J_CP = 10 Hz, C_m), 130.8 (dd, ¹J_CP = 51 Hz, ³J_CP = 2 Hz, C_i), 134.5 (d, ²J_CP = 12 Hz, C_o), 139.9 (d, ⁴J_CP = 2 Hz, C_p).

Elemental analysis calculated for C₃₀H₄₂IP₃Pt (M = 817.5642 g/mol): % C = 44.07%, % H = 5.18%, found % C= 44.84%, % H = 5.23%

Synthesis of 2b

To a suspension of 2 (0.418 g, 0.422 mmol) in toluene was dropwise added a solution of 1,2-diiodoethane (0.119 g, 0.422 mmol) in 1 mL of toluene at −30 °C. The reaction was complete after 2 h, which was confirmed by NMR spectroscopy. Light-brown crystals of 2b (0.198 g, 0.213 mmol, yield 50.5%) were obtained from a toluene solution at −30 °C.

NMR data for 2b:

¹H NMR (C₆D₆, 400 MHz, 298 K δ): 1.24 (d, ³J_PH = 16 Hz, 9H, (CH₃)₃C), 1.68 (d, ³J_PH = 17 Hz, 9H, (CH₃)₃C), 1.99 (s, 9H, p-CH₃–C₆H₄), 6.97 (d, ³J_HH = 7 Hz, 6H, C_Ar–H_m), 7.87 (m, 6H, C_Ar–H_o).

³¹P{¹H} NMR (C₆D₆, 162 MHz, 298 K, δ): 64.2 (dd, ¹J_PP = 520 Hz, ²J_PP = 299 Hz, ¹J_PPt = 1598 Hz, tBu₂P), 21.5 (dd, ²J_PP = 299 Hz, ²J_PP = 6 Hz, ¹J_PPt = 3523, pTol₃P), −30.6 (dd, ¹J_PP = 520 Hz, ²J_PP = 6 Hz, ¹J_PPt = 170 Hz, PI).

¹³C{¹H} NMR (C₆D₆, 100 MHz, 298 K δ): 20.8 (s, p-CH₃–C₆H₄), 31.6 (m, overlapped, (CH₃)₃C), 37.8 (m, (CH₃)₃C), 39.2 (m, (CH₃)₃C), 129.1 (d, ³J_CP = 11 Hz, C_m), 134.6 (d, ²J_CP = 11 Hz, C_o), 140.3 (d, ⁴J_CP = 2 Hz, C_p), C_i not visible in the spectrum.

Elemental analysis calculated for C₂₉H₃₉I₂P₃Pt (M = 929.4342 g/mol): % C = 37.47%, % H = 4.23%, found % C = 38.01%, % H = 4.29%.

Synthesis of 2c

To a suspension of 2 (0.373 g, 0.376 mmol) in 4 mL of DME was dropwise added 1.32 mL of a solution of 1,6-dibromohexane (0.376 mmol, C_M = 0.284 M) at −30 °C. The reaction mixture was allowed to warm to room temperature, and NMR spectra were acquired. The reaction was complete (no signals of the starting complex) after 30 min. The solvent was evaporated, and the oily residue was partially dissolved in pentane. A small amount of yellow crystals of 2c suitable for X-ray analysis were obtained upon dilution of the pentane solution at room temperature.

NMR data for 2c:

¹H NMR (C₆D₆, 400 MHz, 298 K δ): 0.94 (m, overlapped, 6H, PCH₂ and CH₂), 1.33 (m, overlapped, 4H, CH₂), 1.42 (d, ³J_PH = 15 Hz, 9H, C(CH₃)₃), 1.51 (d, ³J_PH = 16 Hz, 9H, C(CH₃)₃), 1.78 (broad m, 2H, BrCH₂), 1.90 (s, 9H, p-CH₃–C₆H₄), 6.94 (m, 6H, C_Ar–H_m), 7.86 (m, 6H, C_Ar–H_o).

³¹P{¹H} NMR (C₆D₆, 162 MHz, 298 K, δ): 54.8 (dd, ¹J_PP = 483 Hz, ²J_PP = 299 Hz, ¹J_PPt = 1694 Hz, tBu₂P), 23.4 (dd, ²J_PP = 299 Hz, ²J_PP = 8 Hz, ¹J_PPt = 3606 Hz, pTol₃P), −68.0 (dd, ¹J_PP = 483 Hz ²J_PP = 8 Hz, ¹J_PPt = 432 Hz, P(CH₂)₆Br).

¹³C{¹H} NMR (C₆D₆, 100 MHz, 298 K δ): 20.0 (dd, ¹J_CP = 50 Hz, ²J_CP = 7 Hz, PCH₂), 20.8 (s, p-CH₃–C₆H₄), 27.6 (s, CH₂), 30.0 (m, CH₂), 30.8 (m, CH₂), 31.6 (broad d, ²J_CP = 8 Hz, C(CH₃)₃), 32.2 (broad m, C(CH₃)₃), 32.4 (s, CH₂)), 33.2 (s, CH₂), 36.1 (m, C(CH₃)₃), 37.6 (m, C(CH₃)₃), 128.9 (d, ³J_CP = 11 Hz, C_m), 130.7 (d, ¹J_CP = 50 Hz, C_i), 134.6 (d, ²J_CP = 12 Hz, C_o), 139.9 (broad s, C_p).

Synthesis of 3

A slightly modified version of the synthesis of [(dppe)Pt(η²-tBu₂P=P)] previously described in the literature was used.¹³ A solution of dppe in toluene was added to a suspension of 2 in toluene at room temperature, and the mixture was stirred for 2–3 days. The volume of the solution was decreased to a quarter of the original volume and it was stirred for another day. Then, the solution was layered with two volumes of petroleum ether, and the resulting precipitate was washed with a 1:2 toluene/ether mixture, resulting in pure [(dppe)Pt(η²-tBu₂P=P)] as a solid (∼60% yield).

NMR data for 3: see ref (13).

Synthesis of 3a

To a suspension of 3 (0.385 g, 0.5 mmol) in toluene was dropwise added 0.577 mL of a solution of methyl iodide (0.5 mmol, C_M = 0.653 M) at −30 °C. The reaction mixture was then warmed to room temperature, and a large amount of white solid formed. The solvent was evaporated, and the solid residue was dissolved in THF. Colorless crystals of 3a (290 mg, 0.295 mmol, 60% yield) were obtained from the THF solution at −20 °C.

NMR data for 3a:

¹H NMR (CDCl₃, 400 MHz, 298 K δ): 0.99 (m, 3H, PCH₃), 1.11 (d, ³J_PH = 16 Hz, 9H, C(CH₃)₃), 1.16 (d, ³J_PH = 16 Hz, 9H, C(CH₃)₃), 1.18 (m, 4H, THF), 2.50 (broad m, 2H, CH₂, dppe), 2.87 (broad m, 2H, CH₂, dppe), 3.67 (m, 4H, THF), 7.31–7.56 (m, overlapped, 16 H, C_Ar-H), 7.66 (m, overlapped, 2H, C_Ar-H), 7.82 (m, overlapped, 2H, C_Ar-H).

³¹P{¹H} NMR (CDCl₃, 162 MHz, 298 K, δ): 54.5 (ddd, ¹J_PP = 455 Hz, ²J_PP = 230 Hz, ²J_PP = 24 Hz, ¹J_PPt = 1710 Hz, tBu₂P), 51.2 (dd, ²J_PP = 230 Hz, ²J_PP = 36 Hz, ¹J_PPt = 2990 Hz, dppe), 49.9 (dd, ²J_PP = 71 Hz, ²J_PP = 24 Hz, ¹J_PPt = 2774 Hz, dppe), −130.8 (ddd, ¹J_PP = 455 Hz, ²J_PP = 71 Hz, ²J_PP = 36 Hz, ¹J_PPt 290 Hz, PMe).

¹³C{¹H} NMR (CDCl₃, 100 MHz, 298 K δ): 5.13 (dd, ¹J_CP = 52 Hz, ²J_CP = 8 Hz, ³J_CP = 4 Hz, PCH₃), 25.6 (s, THF), 28.3 (dd, ²J_CP = 37 Hz, ²J_CP = 13 Hz, CH₂, dppe), 30.6 (ddd, ²J_CP = 37 Hz, ²J_CP = 11 Hz, ³J_CP = 4 Hz CH₂, dppe), 31.7 (d, ²J_CP = 9 Hz, C(CH₃)₃), 31.8 (m, overlapped, C(CH₃)₃), 36.3 (broad m, C(CH₃)₃), 38.2 (broad m, C(CH₃)₃), 68.0 (s, THF), 129.2–134.2 (m, overlapped, C_Ar, dppe).

Elemental analysis calculated for C₃₉H₅₃IOP₄Pt (M = 983.7210g/mol): % C = 47.62%, % H = 5.43%, found % C = 47.60%, % H = 5.54%.

Synthesis of 3b

To a suspension of 3 (0.385 g, 0.5 mmol) in 4 mL toluene was dropwise added a solution of 1,2-diiodoethane (0.141 g, 0.500 mmol) in 1 mL of toluene at −30 °C. The solvent was evaporated, and the solid residue was partially dissolved in toluene and the rest was dissolved in DCM. A small amount of orange solid (polyphosphorus compounds) was not soluble in any accessible solvent. After evaporation of the toluene, the oily residue of tBu₂PI⁴⁸ remained, which was confirmed by NMR spectroscopy. Large yellow crystals of 3b(42) were obtained from a DCM solution at −30 °C.

Synthesis of 3c

To a suspension of 3 (0.308 g, 0.400 mmol) in 4 mL of DME was dropwise added 0.847 mL of a solution of 1,2-dibromoethane (0.400 mmol, C_M = 0.472 M) at −30 °C. Then, the mixture was allowed to warm to room temperature, and a substantial amount of yellow residue formed during heating. The residue was washed with toluene and dissolved in DCM. The DCM solution was further layered with toluene, and large, light-green crystals of 3c (0.111 g, 0.108 mmol, yield 27%) suitable for X-ray analysis were obtained at room temperature.

NMR data for 3c:

¹H NMR (CDCl₃, 400 MHz, 298 K δ): 0.82 (broad d, overlapped, ³J_PH = 16 Hz, 36H, C(CH₃)₃), 1.54 (broad s, 2H, CH₂, dppe), 2.12 (broad s, 2H, CH₂, dppe), 2.77 (broad s, 2H, CH₂, dppe), 3.16 (broad s, 2H, CH₂, dppe), 5.31 (s, 4H, CH₂Cl₂), 7.36 (broad, s, 4H, C_Ar–H), 7.52 (broad, s, 18H, C_Ar–H), 7.71 (broad, s, 14H, C_Ar–H), 8.14 (broad, s, 4H, C_Ar–H).

³¹P{¹H} NMR (CDCl₃, 162 MHz, 298 K, δ): 67.9 (m, tBu₂P), 50.1 (d, ²J_PP = 120 Hz, dppe), 47.1 (m, dppe), −120.1 (m, P).

¹³C{¹H} NMR (CDCl₃, 100 MHz, 298 K δ): 30.2 (m, CH₂, dppe), 30.6 (m, CH₂, dppe), 31.4 (broad s, C(CH₃)₃), 37.2 (very broad m, C(CH₃)₃), 40.4 (very broad m, C(CH₃)₃), 53.4 (s, CH₂Cl₂), 129.7 (broad s, C_Ar, dppe), 130.5 (broad m, overlapped, C_Ar, dppe), 131.5 (broad m, overlapped, C_Ar, dppe), 132.6 (broad m, overlapped, C_Ar, dppe), 133.4 (broad m, overlapped, C_Ar, dppe), 134.7 (broad m, overlapped, C_Ar, dppe).

Elemental analysis calculated for C₃₆H₄₆BrCl₄P₄Pt (M = 1019.44 g/mol): % C = 42.41%, % H = 4.55%, found % C = 42.66%, % H = 4.60%.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.inorgchem.0c00091.

• Crystallographic details, spectroscopic details, and computational details (PDF)

Accession Codes

CCDC 1963412–1963419 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

The authors declare no competing financial interest.