Skip to main content
NCBI home page
ACS AuthorChoice logoLink to ACS AuthorChoice
. 2026 Jun 29;65(27):15640–15650. doi: 10.1021/acs.inorgchem.6c01373

Bis(pyridino‑o‑carboranyl)phosphenium Cation: A Platform for Dual-Site Reactivity

Shiv Kumar a, Deependra Bawari a,b,*, Roman Dobrovetsky a,*
PMCID: PMC13370872  PMID: 42370987

Abstract

Phosphenium salt, [L 2 P + ]­[B­(C6F5)4], substituted by two pyridino-ortho-carboranyl groups (L), was prepared, fully characterized, and its preliminary reactivity with small molecules was studied. Surprisingly, cation [L 2 P + ]­[B­(C6F5)4] reacts differently with O–H and N–H bonds. With RO–H (R = H, Me, Ph), the reaction takes place at P center in [L 2 P + ]­[B­(C6F5)4], via hydrolysis or alcoholysis of the P–C bonds, leading to the carboranopyridinium salt ([LH 2 + ]­[B­(C6F5)4]) and the complementary (RO)2P­(O)­H. In contrast, the reaction of [L 2 P + ]­[B­(C6F5)4] with R2N–H (Et2NH, Ph­(H)­NH, i Pr­(H)­NH) does not proceed at the P center, but takes place at the ortho-carboranyl (oCb) moiety by deboronation, producing zwitterionic phosphenium (L­(L nido )­P + ), with significant reduction in the reactivity of the P center compared to L 2 P + . Remarkably, [L 2 P + ]­[B­(C6F5)4] reacts with SO2 in MeCN at both sites, the P and oCb, stripping both oxygens from sulfur, leading to zwitterionic phosphonium sulfide (L­(L nido )­P + S).

graphic file with name ic6c01373_0016.jpg

graphic file with name ic6c01373_0014.jpg

Introduction

Transition metals (TMs) are well-known for their ability to activate small molecules and for their central role in catalysis. For a long time, this reactivity was considered the exclusive domain of TMs, but over the past two decades, this dogma has been challenged by significant advances in main-group (MG) chemistry. A variety of intriguing low-valent MG compounds capable of engaging in small-molecule activation have been prepared, − and the introduction of frustrated Lewis pairs (FLPs) propelled the field further, establishing MG species as potential alternatives for small-molecule activation and catalysis.

In recent years, the concept of applying structural constraints (SC) to MG centers has attracted considerable attention as an effective strategy for generating highly reactive MG compounds capable of small-molecule activation. Among structurally constrained MG centers, phosphorus stood out for its ability to access two stable oxidation states, typically cycling between PIII and PV. Several structurally constrained neutral PIII species have been reported and shown to activate various small molecules; however, the catalysis using these species was rather limited. In contrast, structurally constrained phosphenium cations (I–III) introduced by our group (Figure ) were found to be capable not only of small-molecule activation but also of metallomimetic catalysis, involving analogous key steps such as “oxidative addition” (OA) → “ligand metathesis” (LM) → “reductive elimination” (RE). For example, SC PIII cation I has been employed in the metallomimetic hydrosilylation of aldehydes (Figure ); II was used in the hydrodefluorination and amination of electron-poor fluoroarenes (Figure ). Since then, other groups have also become interested in this approach and reported the synthesis of SC phosphenium cations that showed reactivity toward strong bonds.

1.

1

Open in a new tab

Examples of previously reported SC PIII cations (I–III), and PIII cation (L 2 P +) reported in this work.

In recent years, oCb-based ligands have emerged as powerful tools for enhancing the reactivity of MG centers, particularly by amplifying their Lewis acidity. Such as exemplified by Wang and co-workers, who strategically designed an oCb-substituted borenium cation that enabled activation of inert bonds, including H3C–H. Martin reported the synthesis of oCb3B and oCb2BH benchmark Lewis superacids, noted for their exceptional reactivity. Ye reported 3D analogues of 9,10-diboraanthracene and 9-borafluorene that operate as neutral, boron-centered Lewis superacids, expanding the structural and functional diversity of this class. Peryshkov demonstrated the redox-active potential of oCb scaffolds, enabling N–H bond activation in ammonia using an ortho-carboranyl diphosphine. Very recently, Dutton reported the first oCb-supported hypervalent iodine­(III) type species, which was found to be more reactive than any known aryl hypervalent iodine­(III) compound.

Recently, our group used the high electron-withdrawing ability of oCb to synthesize SC phosphenium cation III (Figure ), which was used for the hydrogenation of C=C double bonds and fused aromatic systems. Motivated by this result, we aimed at synthesizing a modified version of III, L 2 P + , in which the strain is slightly released, and an additional pyridinyl donor is attached to increase the stability of this phosphenium cation (Figure ). We envisioned that one of the pyridyl donors in L 2 P + could be detached from the P center by heating, exposing the ambiphilicity of this center.

Herein, we report the synthesis, isolation, and preliminary reactivity studies of [L 2 P + ]­[B­(C6F5)4]. Interestingly, unlike previous PIII cationic and neutral analogs, [L 2 P + ]­[B­(C6F5)4] reacts differently with O–H and N–H bonds; while the former reacts with the cationic PIII center, the latter reacts at the oCb moiety. Remarkably, in the reaction with SO2 in MeCN, both sites (P and oCb) react, stripping both oxygen atoms of sulfur.

Results and Discussion

First, we decided to prepare L 2 PCl, which, after Cl– abstraction, should lead to the desired L 2 P + (Scheme ). To synthesize L 2 PCl, we first deprotonated pyridinocarborane (LH) with n BuLi, and then reacted it with 0.5 equiv of PCl3 in a one-pot reaction. This, however, did not result in the formation of L 2 PCl but led to a mixture of products. We, thus, decided to attempt the stepwise approach. First, we reacted deprotonated LH (LLi) with a slight excess of PCl3 (1.1 equiv), which cleanly led to LPCl 2 (Scheme ). LPCl 2 was isolated in 89% yield by crystallization from CHCl3. The molecular structure of LPCl 2 was determined by single-crystal X-ray diffraction (SC-XRD) (Figure a). Importantly, the P–N distance in LPCl 2 of 2.335 Å indicates the absence of a bonding interaction between these two centers. Isolated LPCl 2 was reacted with an additional equivalent of LLi; this, as well, did not yield the target compound L 2 PCl. An in situ 31P NMR revealed a single new phosphorus-containing species, displaying a sharp singlet at 76.8 ppm. While in the 1H and 13C NMR spectra, in addition to the expected signals of the pyridine moieties, several unexpected upfield signals were also observed. 1H–13C HSQC and HMBC NMR experiments showed a doublet of doublets at 4.63 ppm in the 1H NMR spectrum (J = 12 Hz, 6 Hz) correlated to a doublet at 56.42 ppm in the 13C NMR spectrum (J C–P = 19 Hz), indicative of an aliphatic CH fragment. Additionally, signals at 6.21, 5.60, and 5.39 ppm in the 1H NMR spectrum correlated to resonances at 125.1, 104.8, and 117.4 ppm in the 13C NMR spectrum. These data suggested the presence of a conjugated olefinic moiety (see Figures S8–S15). Overall, the spectral data indicated the formation of an unsymmetrical species featuring a dearomatized pyridine ring.

1. Attempted Synthesis of L 2 PCl, Formation of L’LP via a Reaction of LPCl 2 and LLi .

1

Open in a new tab

2.

2

Open in a new tab

Molecular structure of (a) LPCl 2, and (b) L’LP. Thermal ellipsoids have been adjusted to the 50% probability level; hydrogen atoms were omitted for clarity.

The clean product was isolated by crystallization from toluene. The SC-XRD of these crystals confirmed the identity of the product as L’LP (Figure b). The phosphorus center is bonded to two carbons (P1–C1 = 1.891 Å, P1–C7 = 1.940 Å) from two ligands and to a nitrogen (P1–N1 = 1.754 Å) of the dearomatized pyridine ring. The dearomatization is evident from the puckering of the ring and elongation of the C4–N1 (1.470 Å) and adjacent C–C (1.508 Å) bond distances (Figure b).

The formation of compound L’LP likely originates from the slow generation of L 2 PCl, which, upon formation, reacts rapidly with a second equivalent of LLi (Scheme ). The observed regioselectivity can be attributed to the LUMO being localized at the ortho position (see ESI, Figure S74).

The inability to obtain L 2 PCl and the formation of L’LP prompted us to try to get the desired cation L 2 P + from it. We hypothesized that, upon heating, the L’LP system could dissociate into the desired L 2 P + with the L – counteranion, driven by rearomatization of the pyridine ring. If the L – could be trapped, then the desired L 2 P + could be obtained. We thus decided to react L’LP with MeOTf. As a result, after 12 h, we were pleased to find that a reaction of L’LP with MeOTf resulted in the formation of the desired [L 2 P + ]­[OTf] and the complementary LMe at r.t. (Scheme ). This transformation was evidenced by the appearance of a new signal at 30 ppm (CH3CN) in the 31P NMR spectrum and the emergence of a more symmetric pattern in both 1H and 13C NMR spectra, accompanied by the complete disappearance of features associated with the dearomatized pyridine moiety. The observed downfield shift in the 31P NMR signal is significantly lower than that reported for previously characterized cationic PIII species (δ > 100 ppm), ,, suggesting a more electron-rich phosphorus center in L 2 P + . This may be attributed to additional coordination at the phosphorus center by the nitrogen atom of a second pyridine ring.

2. Synthesis of [L 2 P + ]­[B­(C6F5)4].

2

Open in a new tab

Due to the poor solubility of [L 2 P + ]­[OTf], the TfO– was replaced by the (C6F5)4B– anion by an ion exchange reaction of [L 2 P + ]­[OTf] with K­[B­(C6F5)4], affording [L 2 P + ]­[B­(C6F5)4] (Scheme ). [L 2 P + ]­[B­(C6F5)4] was purified by crystallization from a CH2Cl2:CHCl3 mixture (1:1.5), and its molecular structure was determined by SC-XRD (Figure ).

3.

3

Open in a new tab

Molecular structure of [L 2 P +]­[B­(C6F5)4]. Thermal ellipsoids have been adjusted to the 50% probability level; hydrogen atoms and (C6F5)4B– were omitted for clarity.

The phosphorus center in the L 2 P + cation adopts a tetracoordinate, slightly distorted seesaw geometry, with bond angles of ∠C1–P1–C2 = 108.81° and ∠N1–P1–N2 = 173.84°. The P1–C1 and P1–C2 (1.910 and 1.913 Å, respectively) bond lengths are slightly longer than a typical covalent P–C bond length, while the P1–N1 and P1–N2 (2.054 and 2.031 Å, respectively) are significantly longer than typical covalent P–N bonds. , As well as elongated considerably in comparison to the coordinative P→N bond lengths in previously reported SC phosphenium cations. ,, This elongation is likely a consequence of the 3c-4e interaction involving the axial pyridine ligands, which weakens the N→P interactions via donation along the coordination axis. Notably, a similar bonding motif has previously been reported for similar species.

To gain deeper insight into the electronic structure of cation L 2 P + , density functional theory (DFT) calculations were performed at the B3LYP-D3­(BJ)/6–311++G­(d,p) level of theory. , The optimized geometry of L 2 P + is in good agreement with its experimental X-ray molecular structure (see Table T1 in ESI). Frontier molecular orbital (FMO) analysis reveals that the HOMO is primarily localized on the phosphorus center, whereas the LUMO is distributed over the π*-orbitals of the pyridine rings (Figure a). Natural Bond Orbital (NBO) analysis indicates a σ-type lone pair on the phosphorus atom with an occupancy of 1.93 electrons and sp0.52 hybrid character. Natural Population Analysis (NPA) charges show a significant positive charge on phosphorus (+1.315) and negative charges on nitrogen (−0.544) and carbon (−0.687) atoms.

4.

4

Open in a new tab

a) HOMO and LUMO orbitals (isovalue 0.05) of L 2 P +; b) AIM analysis of L 2 P +.

The Wiberg Bond Index (WBI) values indicate partial single-bond character for the P–N bonds (0.383), while the P–C bonds (0.782) exhibit predominantly single-bond character. Bader’s Atoms in Molecules (AIM) analysis further clarifies bonding interactions: the bond critical point (BCP) of the P1–N1 bond exhibits a positive Laplacian of electron density (∇2ρ = 0.00524), low electron density (ρ = 0.0818), the relationships G­(r) ≪ |V(r)| and a negative total energy density normalized by electron density (H b /ρ­(r) = – 0.4320) at the BCP, consistent with a donor–acceptor type interaction (Figure b). In contrast, the AIM parameters for the P–C bonds are indicative of covalent bonding. Collectively, these computational and experimental findings corroborate the description of L 2 P + as a bipyridyl-supported phosphenium cation.

Having [L 2 P + ]­[B­(C6F5)4] in hand, we started studying its reactivity with small molecules. First, [L 2 P + ]­[B­(C6F5)4] was reacted with one equiv of H2O in CDCl3, and the reaction progress was monitored by 31P NMR spectroscopy at r.t., after 5 min approximately 40% of [L 2 P + ]­[B­(C6F5)4] was consumed. The 31P NMR spectrum was recorded, which showed a doublet at 13.53 ppm (J­(PH) = 646 Hz), indicating the formation of a P–H moiety, which was corroborated by a corresponding doublet at 7.36 ppm (J­(PH) = 646 Hz) in the 1H NMR spectrum. After 30 min, the NMR picture remained the same, with [L 2 P + ]­[B­(C6F5)4] still present in the reaction mixture. The addition of excess (5 equiv) H2O resulted in complete consumption of [L 2 P + ]­[B­(C6F5)4]. Interestingly, the 1H NMR spectrum also displayed a broad singlet at 15.94 ppm, attributed to a pyridinium N–H fragment. These resonances are consistent with the formation of the protonated ligand LH 2 + . Over time, crystals precipitated from the reaction mixture, and the SC-XRD analysis confirmed the formation of [LH 2 + ]­[B­(C6F5)4] (see Figure S30). Overall, combined 1H and 31P NMR data and the isolation of [LH 2 + ]­[B­(C6F5)4] clearly indicate that the P-containing product of this reaction is (HO)2P­(O)H (Scheme ). , Notably, analogous reactivity was observed with MeOH and PhOH, yielding the corresponding alcoholysis products, (MeO)2P­(O)H and (PhO)2P­(O)­H, , respectively; however, unlike in the case with H2O, heating to 85 °C was required for these reactions to proceed (see ESI for more details).

3. Reactivity of [L 2 P + ]­[B­(C6F5)4] with ROH (R = H, Me, Ph).

3

Open in a new tab

This type of reactivity is very unusual for P–C bonds in PIII compounds, which are typically robust and resistant to hydrolysis and, more so, to alcoholysis. The observed reactivity is usually associated with P–X (X = Cl, Br, I), meaning that in the case of [L 2 P + ]­[B­(C6F5)4], the oCb moiety acts as a pseudohalide. , To examine whether this behavior is intrinsic to the P–C bonds in phosphinocarboranes, we treated Ph2P­(oCb) with H2O and MeOH. No hydrolysis or alcoholysis of Ph2P­(oCb) was observed, even after prolonged heating (see ESI Scheme S12 for more details). This indicates that the observed hydrolysis (alcoholysis) of L 2 P + represents an atypical case rather than a general property of phosphinocarboranes. The hydrolysis (alcoholysis) of the P–C bonds in L 2 P + likely arises due to their high polarity (Pδ+–Cδ−) along with the stabilization of the cationic intermediates by the pyridinyl moiety (see ESI for more details, Figure S44).

Next, we tested the reactivity of [L 2 P + ]­[B­(C6F5)4] with amines. First, a reaction between [L 2 P + ]­[B­(C6F5)4] and an equiv of Et2NH was performed in CDCl3, and its progress was monitored using 31P NMR spectroscopy at r.t.. In 31P NMR, after 1 h, the signal at 36 ppm, corresponding to L 2 P + , decreased, and a new signal appeared at 78 ppm. After 3 h, an additional signal at 69 ppm emerged, with approximately 50% of [L 2 P + ]­[B­(C6F5)4] consumed. Two additional equiv of Et2NH were added, which finally led to 69 ppm as the major signal, while the signals at 35 and 78 ppm completely disappeared (see ESI).

Upon completion of the reaction, CDCl3 was evaporated, and the remaining solid was washed with C6H6. The 31P NMR of both fractions was measured, showing that only C6H6 had P-containing products dissolved in it. Slow evaporation of the C6H6 resulted in the formation of crystals. SC-XRD analysis of these crystals revealed the molecular structure of the product as zwitterionic phosphenium L­(L nido )­P + (Figure ). Interestingly, a number of zwitterionic P­(I) compounds have been previously reported,13c‑d while the zwitterionic phosphenium cations are rare.

5.

5

Open in a new tab

Molecular structure of L­(L nido )­P +. Thermal ellipsoids have been adjusted to the 50% probability level; nonrelevant hydrogen atoms were omitted for clarity.

The formation of L­(L nido )­P + as the only P-containing product indicates that Et2NH reacted with the oCb moiety via a deboronation reaction, , and not at the PIII cationic center (Scheme ). Importantly, the reaction of [L 2 P + ]­[B­(C6F5)4] with other amines, such as PhNH2, i PrNH2, and 2,4,6-trimethylaniline, as well as with MeCN, also afforded L­(L nido )­P + , but required heating to 85 °C (Scheme ). It is important to note that, unlike in the reaction of [L 2 P + ]­[B­(C6F5)4] with amines, where changes in the 11B NMR spectra were observed and attributed to formation of a B3-amine adduct, , no significant changes in the 11B NMR spectra were detected at any stage during the reactions of [L 2 P + ]­[B­(C6F5)4] with ROH (R = H, Me, Ph) (see Figures S32 and S33). These observations indicate that, unlike amines, which react directly with the oCb cage in [L 2 P + ], water and alcohols preferentially react at the P center.

4. Reactivity of [L 2 P + ]­[B­(C6F5)4] with RR’NH (RR’NH = Et2NH, PhNH2, and iPrNH2) Formation of L­(L nido )­P + .

4

Open in a new tab

The structure of L­(L nido )­P + features a tetracoordinate phosphorus center that adopts a seesaw geometry, with key bond angles of ∠C1–P1–C3 = 105.02° and ∠N1–P1–N2 = 168.93°. The P1–N2 and P1–C3 (1.947 and 1.868 Å, respectively) bond lengths are shorter than the P1–N1 and P1–C1 (2.180 and 1.922 Å, respectively) bond lengths, indicating a stronger bonding of the nido oCb fragment to the P center. This can be explained by the fact that the nido cluster is anionic, and thus more electron-rich compared to closo oCb, which results in a stronger donor ability of the adjacent pyridine nitrogen, while the pyridine nitrogen bound to the electron-withdrawing closo oCb remains a weak donor.

To compare the electronic structures of L 2 P + and L­(L nido )­P + , the structure of L­(L nido )­P + was DFT computed (B3LYP-D3­(BJ)/6–311++G­(d,p)). , The optimized geometry is in good agreement with the experimentally determined solid-state structure (see ESI Table T2). MO analysis reveals that, in contrast to L 2 P + , where the phosphorus lone pair constitutes the HOMO, in L­(L nido )­P + , the lone pair at phosphorus corresponds to the HOMO–1­(Figure ), while the HOMO is primarily localized on the nido-carborane fragment (see ESI, Figure S73). The LUMO is mainly distributed over the π* system of the pyridine ring attached to the nido-carborane moiety (Figure ). NBO analysis indicates the presence of a σ-type lone pair at phosphorus with an occupancy of 1.94 electrons and an sp0.58 hybridization. NPA charges show that P1 bears a positive charge of +1.261, which is slightly lower than in L 2 P + (+1.315). Both N1 and N2 are negatively charged (−0.501 and – 0.587, respectively). The WBI values highlight the asymmetric bonding environment at phosphorus. The P1–N2 bond exhibits a WBI of 0.4913, whereas the P1–N1 bond shows a significantly lower value of 0.2532, indicating a stronger P1–N2 interaction and a weaker P1–N1 bond. This asymmetry reflects the electronic consequences of the deboronation process - conversion of the closo cluster into the nido form strengthens the P1–N2 interaction.

6.

6

Open in a new tab

(a) HOMO–1 and LUMO orbitals (isovalue 0.05) of L­(L nido )­P +; (b) AIM analysis of L­(L nido )­P +.

AIM analysis further supports this picture. The bond critical point (BCP) for P1–N1 shows a positive Laplacian of the electron density (∇2ρ = +0.06177) and relatively low electron density (ρ = 0.05627), consistent with a weak coordination-type interaction. In contrast, the P1–N2 BCP exhibits a near-zero, slightly negative Laplacian (∇2ρ = – 0.004420) and a significantly higher electron density (ρ = 0.10682) (Figure ), indicative of a strong coordinative bond with substantial covalent character. Collectively, these computational data indicate that the P1–N1 interaction is best described as a weak donor–acceptor contact, whereas P1–N2 represents a strong coordinative bond with pronounced covalent character.

These structural and electronic differences suggest that the reactivity of L­(L nido )­P + should differ significantly from that of the parent phosphenium cation L 2 P + , potentially accounting for their distinct reactivity profiles. This expectation was confirmed experimentally. A catalytic amount of L 2 P + (5 mol %) rapidly polymerizes THF at room temperature within approximately 10 min (Scheme ), dimerizes 1,1-diphenylethylene at r.t. after 24 h (Scheme ), and immediately catalyzes (5 mol %) the cyanosilylation of benzaldehyde using TMSCN (Scheme ). In contrast, L­(L nido )­P + is completely inactive toward THF and 1,1-diphenylethylene under identical conditions and does not promote cyanosilylation (Scheme ). These findings indicate that B-vertex decapitation and formation of L­(L nido )­P + substantially reduce the Lewis acidity relative to L 2 P + (see ESI for a comparison of the FIA values of L 2 P + , L­(L nido )­P + , and other reported phosphenium cations), thereby suppressing its catalytic activity.

5. Experimental Differences in the Reactivities of L 2 P + vs L­(Lnido)­P + .

5

Open in a new tab

Importantly, the finding that deboronation of the oCb substituent directly impacts the reactivity of the MG element bound to it highlights an attractive strategy for reactivity control. For instance, selective deboronation, as in the conversion of L 2 P + to L­(L nido )­P + , can be employed as a deliberate tool to “tune down” or completely “shut down” the Lewis acidity without altering much the core structure of the ligand framework. This approach introduces an additional level of flexibility in ligand design, enabling precise modulation of reactivity profiles in catalysis and small-molecule activation.

In an effort to probe the reactivity of L 2 P + at both sites (the P and oCb), we reacted [L 2 P + ]­[B­(C6F5)4] with SO2, an ambiphilic substrate, in CD3CN and monitored the reaction progress by 31P NMR spectroscopy (Scheme ). No reaction was observed at r.t., however, after heating at 100 °C for 3 h, in addition to the signal at δ = 31 ppm (in CD3CN) corresponding to L 2 P + , a new signal appeared at δ = – 1.9 ppm (see ESI, Figure S53). After 6 h, another signal appeared at 26.4 ppm, which, after 48 h, was the only signal in 31P NMR.

6. Reactivity of [L 2 P + ]­[B­(C6F5)4] with SO2 at Both Reactive Sites, the P Center and the oCb Moiety, Leading to L­(L nido )­P + S .

6

Open in a new tab

Over time, crystals precipitated from the reaction mixture (CD3CN). The SC-XRD analysis of these crystals revealed their identity as a nido-zwitterionic phosphonium sulfide species (L­(L nido )­P + S) (Figure ). In contrast to L­(L nido )­P + , compound L­(L nido )­P + S exhibits only slight differences between the P–N and P–C bond lengths: P1–N1 = 2.030 Å, P1–N2 = 1.980 Å, and P1–C1 = 1.890 Å, P1–C8 = 1.860 Å. This can be explained by the fact that the PV cationic center in L­(L nido )­P + S is significantly more electron-poor compared to the PIII cationic center in L­(L nido )­P + , which results in a contraction of the substituents toward the phosphorus atom. The PS bond length is 1.938 Å, consistent with a typical PS double bond.

7.

7

Open in a new tab

Molecular structure of L­(Lnido)­P + S. Thermal ellipsoids have been adjusted to the 50% probability level; nonrelevant hydrogen atoms were omitted for clarity.

The formation of L­(L nido )­P + S could potentially be explained by cooperative engagement of the two reactive sites present in L 2 P + : the PIII center and the oCb moiety. We speculate that, rather than acting independently, these sites operate synergistically, and that this dual-site reactivity, assisted by MeCN-induced deboronation (see above) of L 2 P + , ultimately enables the cleavage of both SO bonds. It is important to note that the fate of the boron species generated upon oCb decapitation is difficult to follow; however, related species have previously been shown to deoxygenate organic molecules. , To support this hypothesis, we conducted two control experiments: (i) the reaction of isolated L­(L nido )­P + with SO2 in CH2Cl2 (see ESI), and (ii) the in situ formation of L­(L nido )­P + from L 2 P + and MeCN, followed by the addition of SO2 (see ESI). In both cases, L­(L nido )­P + S was not formed. Instead, prolonged heating of both reactions at 100 °C resulted in a complex mixture of products (see ESI, Figures S54 and S55). Although this proposal remains preliminary and more detailed mechanistic studies are required to fully elucidate the reaction pathway, these experiments support our hypothesis that, in the direct reaction of L 2 P + with SO2 in MeCN, both the P and oCb sites act cooperatively.

Conclusions

In summary, we synthesized, isolated, and characterized the phosphenium salt [L 2 P + ]­[B­(C6F5)4]. Preliminary reactivity studies of [L 2 P + ]­[B­(C6F5)4] showed that it has two reactive sites: one is the cationic PIII center, and the second is the oCb moiety. In reactions with ROH (R = H, Me, Ph), L 2 P + reacts through the P center, leading to the hydrolysis (or alcoholysis) of the P–C bonds, giving (RO)2P­(O)H (R = H, Me, Ph). In contrast, L 2 P + reacted with R2NH (R2NH = Et2NH, PhNH2, i PrNH2) through deboronation of the oCb moiety, producing a zwitterion L­(L nido )­P + . We found that the reactivity of L­(L nido )­P + is significantly diminished compared to L 2 P + , which can provide an interesting avenue for modulating the chemical properties, such as acidity or basicity, of MG centers by modification of oCb-based periphery. Finally, in the reaction with SO2 in MeCN, L 2 P + reacted at both reactive sites, leading to L­(L nido )­P + S, in which both of the oxygens are stripped of the S center. We continue our research on MG reactive centers and carborane-based substituents.

Experimental Section

Safety Statement

No unexpected, unusual, or unusually hazardous materials, conditions, or procedures were encountered in this study.

General Considerations

All preparations were carried out under an anhydrous N2 atmosphere using standard Schlenk and glovebox techniques. All glassware was oven-dried and cooled under vacuum before use. Commercial reagents were purchased from Sigma-Aldrich, Yunali Tech., Stream, or Apollo Scientific and used without further purification unless indicated otherwise. LH and SO 2 were prepared following the reported procedures. , NMR spectra were recorded at room temperature using a Bruker AvanceIII-400 MHz spectrometer. Data for 1H NMR are reported as follows: chemical shift (δ ppm), integration, multiplicity (s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet, br = broad, brs = broad singlet), coupling constant (Hz), assignment. High-resolution mass spectrometry was performed with a Waters SYNAPT G2-S.

Synthesis of LPCl2

n BuLi (1.0 equiv., 1.87 mL, 3.0 mmol, 1.6 M in hexanes) was added to Et2O solution (20 mL) of LH (663 mg, 3.0 mmol) at 0 °C. The reaction mixture was left in a cold bath to warm slowly to room temperature. The appearance of a light-yellow color indicated the lithiation of LH, and the solution was stirred for an additional hour at room temperature. The mixture was cooled again at 0 °C, and PCl3 (1.1 equiv. 287 μL, 3.3 mmol) was added. The solution was left in a cold bath to warm to room temperature and then stirred for an additional 12 h. After completion of the reaction, all the volatiles were evaporated under vacuum, and the solid was extracted with CH2Cl2 (20 mL). A yellow-white solid was obtained upon evaporation. The solid was crystallized by slow evaporation from a chloroform solution, yielding colorless crystals after 2 days. Overall isolated yields of LPCl 2 were: 863 mg (89%). 1 H NMR (400 MHz, CDCl3); δ = 8.35 (d, J = 4 Hz, 1H), 7.89 (t, J = 8 Hz, 1H), 7.57 (d, J = 8 Hz, 2H), 7.51–7.47 (m, 1H), 3.3–1.7 (br, 10H, carboraneB–H). 13 C­{ 1 H} NMR (100 MHz, CDCl3); δ = 150.29 (d, J = 6 Hz, Ar–CPyridine‑carborane), 144.13 (Ar–CH), 139.53 (Ar–CH), 125.33 (Ar–CH), 121.71 (Ar–CH), 80.73 (d, J = 152 Hz, carboraneC–P), 79.15 (d, J = 7 Hz, carboraneC–P) ppm. 31 P NMR (162 MHz, CDCl3); δ = 111.2 ppm. 11 B NMR (128 MHz, CDCl3); δ = – 10.1 to – 7.9 (m), – 2.0 (d, J = 147 Hz) ppm. HRMS (APCI positive mode): Calc. for C7 H14 10B2 11B8 N P 35Cl1 = 286.1555; found = 286.1558.

Synthesis of L’LP

A 100 mL Schlenk flask equipped with a magnetic stir bar was charged with 30 mL of dry benzene and 700 mg of LPCl 2 (2.17 mmol). The resulting solution was cooled to 0 °C using an ice bath, and a solution of the lithiated ligand (LLi, 2.0 equiv, 4.34 mmol) in benzene was added dropwise over 10 min. After the addition was complete, the reaction mixture was allowed to gradually warm to room temperature and was subsequently stirred for an additional 12 h. After completion of the reaction, all volatiles were removed under vacuum. The resulting solid was extracted with 20 mL CH2Cl2, producing a brownish-red precipitate upon solvent evaporation. This solid was washed with hexane, yielding an off-white product. The isolated yield of the compound was 704 mg (47%). The off-white solid was dissolved in 10 mL of toluene, and after 4 days at room temperature, slow evaporation afforded colorless crystals. 1 H NMR (400 MHz, CDCl3); δ = 8.58 (d, J = 16 Hz, 2H), 7.72–7.66 (m, 3H), 7.43 (d, J = 8 Hz, 1H), 7.41–7.35 (m, 2H), 6.21 (brs, 1H­(H d )), 5.60 (brs, 1H­(H b )), 5.39 (t, J = 6.8, 1H­(H c )), 4.63 (dd, J = 12.0, 6.2 Hz, 1H­(H e )), 3.1–1.7 (br, 30H, carboraneB–H) ppm. 13 C­{ 1 H} NMR (100 MHz, CDCl3); δ = 151.25 (d, J = 4 Hz), 149.92, 149.07, 147.67, 138.36, 137.86, 126.31, 125.96­(C d ), 125.13, 124.52, 122.43, 117.46­(C c ), 104.84­(C b ), 102.61­(C a ), 87.45 (d, J = 11 Hz­(C f )), 85.47­(C g ), 83.16 (d, J = 6 Hz­(C j )), 81.93 (d, J = 87 Hz­(C i )),78.79 (d, J = 4 Hz­(C h )), 71.89 (d, J = 46 Hz­(C k )) 56.41 (d, J = 19 Hz­(C e )) ppm. 31 P NMR (162 MHz, CDCl3); δ = 76.8 ppm. 11 B NMR (128 MHz, CDCl3); δ = – 9.1 to – 1.6 (br) ppm. HRMS (APPI positive mode): Calc. for C21 H42 10B6 11B24 N3 P= 691.6126; found = 691.6129.

Synthesis of [L 2 P + ]­[OTf]

MeOTf (10 equiv) was added dropwise to a 20 mL benzene solution of L’LP (700 mg, 1.01 mmol) under constant stirring. A precipitate gradually formed as the reaction progressed. The mixture was stirred for an additional 12 h at room temperature. The resulting solid was collected by filtration and washed with hexane (3 × 20 mL) to remove excess MeOTf. The obtained off-white solid ([L 2 P + ]­[OTf]; 315 mg, 51% yield) exhibits a singlet at 30.78 ppm in acetonitrile (soluble in dilute solution) and was used in subsequent steps without further purification. [L 2 P + ]­[OTf] exhibited poor solubility in most organic solvents, which precluded its characterization by 1H and 13C NMR. Repeated attempts to obtain a crystal suitable for single-crystal X-ray diffraction analysis were not successful. 31 P NMR (162 MHz, CDCl3); δ = 30.7 ppm.

Synthesis of [L 2 P + ]­[B­(C6F5)4

]: 15 mL of CH2Cl2 was added to a mixture of [L 2 P + ]­[OTf] (500 mg, 0.80 mmol) and [K]­[ B­(C6F5)4] (637 mg, 0.88 mmol). The reaction mixture was stirred for 12 h, then filtered to remove KOTf. The solvent was evaporated under reduced pressure, and the resulting solid was washed thoroughly with hexane (3 × 10 mL) to afford an off-white solid. This material was subsequently dissolved in a CH2Cl2/CHCl3 mixture (1:1.5) and left to crystallize by slow evaporation at room temperature. After 5 days, colorless crystals of [L 2 P + ]­[B­(C6F5)4] were obtained. The SC-XRD analysis of [L 2 P + ]­[B­(C6F5)4], revelaved that K­[B­(C6F5)4] was cocrystallized with it. The isolated yield of the crystal was 670 mg (42%). Notably, for the synthesis of [L 2 P + ]­[B­(C6F5)4], 1.1 equiv K­[B­(C6F5)4] were used, which after washing with hexane result to off white powder [L 2 P + ]­[B­(C6F5)4. Subsequently, the solid [L 2 P + ]­[B­(C6F5)4] was dissolved in CHCl3 to remove insoluble [K]­[ B­(C6F5)4]. The isolated yield of the crystal was 670 mg (72%). 1 H NMR (400 MHz, CDCl3); δ = 8.73 (d, J = 8 Hz, 2H (H d )), 8.37 (t, J = 8 Hz, 2H (H e )), 7.91 (t, J = 8 Hz, 2H (H c )), 7.83 (d, J = 8 Hz, 2H (H b )), 3.5–1.5 (br, 20H, carboraneB–H) ppm. 13 C­{ 1 H} NMR (100 MHz, CDCl3); δ = 149.43 (d, J = 5 Hz, (C a )), 148.09 (d, J C–F = 236 Hz, B­(C6F5)4), 146.41 (d, J = 8 Hz, (C d )), 145.46­(C e ), 138.13 (d, J C–F = 248 Hz, B­(C6F5)4), 136.25 (d, J C–F = 242 Hz, B­(C6F5)4), 126.64­(C c ), 122.76­(C b ), 76.43 (d, J = 11 Hz, (C f )), 70.77 (d, J = 107 Hz, (C g )) ppm. 31 P NMR (162 MHz, CDCl3); δ = 36.0 ppm. 11 B NMR (128 MHz, CDCl3); δ = – 16.7 (s, B­(C6F5)4), – 10.5 to 0.2 (br) ppm. 19 F NMR (376.5 MHz, CDCl3); δ = – 167.2, – 163.1, – 133.2 ppm. HRMS (APCI positive mode): Calc. for C14 H28 10B5 11B15 N2 P= 470.4039; found = 470.4040.

General Procedure for Reaction of [L2P+]­[B­(C6F5)4] with O–H Bond Containing Molecules

In a J-Young NMR tube, a solution of [L 2 P + ]­[B­(C6F5)4] (50 mg, 0.043 mmol) was prepared in 0.5 mL CDCl3 and followed by the addition of an excess amount of the respective alcohols or H2O. The progress of the reaction was monitored by 31P NMR spectroscopy. Notably the reaction with H2O proceeded at r.t. while MeOH and PhOH required heating at 85 °C for 24–48 h.

General Procedure for Reaction of [L2P+]­[B­(C6F5)4] with N–H Bond Containing Molecules or Synthesis of L­(Lnido)­P+

In a J-Young NMR tube, a solution of [L 2 P + ]­[B­(C6F5)4] (50 mg, 0.043 mmol) was prepared in 0.5 mL CDCl3 and followed by the addition of an excess amount of the respective amines. The progress of the reaction was monitored by 31P NMR spectroscopy. Following the completion of the reaction, the solvent was evaporated, and the residue was washed with hexane (2 × 5 mL). The isolated solid exhibits very low solubility in benzene. The product was isolated by crystallization (21 mg, 84%) from a THF:benzene (1:5) mixture via slow evaporation at room temperature. The SC-XRD of these crystals was measured, determining the molecular structure of the obtained product as a zwitterion (L­(L nido )­P + ). Notably the reaction with Et2NH proceeded at r.t. while 2,4,6-trimethylaniline, isopropylamine, and aniline required heating at 85 °C for 24 h. NMR of L­(L nido )­P + : 1 H NMR (400 MHz, CD2Cl2); δ = 8.60 (d, J = 4 Hz, 1H), 8.36 (d, J = 8 Hz, 1H), 8.06 (m, 2H), 7.68 (d, J = 8 Hz, 1H), 7.63 (t, J = 6 Hz, 1H), 7.49 (d, J = 8 Hz, 1H), 7.44 (t, J = 6 Hz, 1H), 2.35 (br, 19H, carboraneB–H), −2.01 (brs, 1H, B–Hbridge) ppm. 13 C­{ 1 H} NMR (100 MHz, CD2Cl2); δ = 166.74 (d, J = 5 Hz), 148.95 (d, J = 6), 144.91 (ArC–H), 143.90 (ArC–H), 142.59 (d, J = 15 Hz), 141.49 (ArC–H), 125.43 (ArC–H), 121.89 (ArC–H), 121.07 (ArC–H), 120.37 (d, J = 3 Hz), 77.45 (d, J = 8 Hz, carboraneC‑Pyridine), 75.40 (d, J = 106 Hz, carboraneC–P) ppm. 31 P NMR (162 MHz, CD2Cl2); δ = 71.0 ppm. 11 B NMR (128 MHz, CD2Cl2); δ = – 32.2 (d, J = 147 Hz), – 29.7 (d, J = 129 Hz), – 21.8 (d, J = 142 Hz), – 19.4 (d, J = 145 Hz), – 15.7 (d, J = 151 Hz), – 9.6 (d, J = 124 Hz), – 7.7 (br), – 3.9 (br) ppm. HRMS (APCI positive mode): Calc. for C14 H26 10B4 11B15 N2 P = 458.3755; found = 458.3752.

General Procedure for Reaction of [L2P+]­[B­(C6F5)4] with SO2 or Synthesis of L­(Lnido)­P+S

A solution of [L 2 P + ]­[B­(C6F5)4] (50 mg, 0.043 mmol) was prepared in 0.7 mL of CH3CN and transferred into a J-Young NMR tube under an inert atmosphere. The tube was degassed two times using freeze–pump–thaw cycles. While the tube was immersed in liquid nitrogen, SO2 was added. The sealed tube was then placed in an oil bath and heated at 100 °C for 48 h.The reaction progress was monitored by 31P NMR spectroscopy. After 3 h, in addition to the signal corresponding to L 2 P + (at 31 ppm in CD3CN), a new signal appeared at δ = – 1.9 ppm, possibly assigned to an adduct formed between SO2 and the boron center of the o-Cb cluster. After 6 h, another signal appeared at 26 ppm, which, after 48 h, was the only signal in 31P NMR. After 5 days, crystals were formed from the reaction mixture. The SC-XRD of these crystals showed the molecular structure as a nido-zwitterionic phosphonium sulfide (L­(L nido )­P + S). NMR of L­(L nido )­P + S: 1 H NMR (400 MHz, DMSO-d 6); δ = 8.99 (d, J = 4 Hz, 1H), 8.81 (d, J = 4 Hz, 1H), 8.08–8.0 (m, 2H), 7.51 (t, J = 8 Hz, 2H), 7.31 (d, J = 8.0 Hz, 1H), 7.24 (d, J = 8 Hz, 1H), 1.23 (br, 19H, carboraneB–H), – 2.51 (brs, 1H, B–Hbridge) ppm. 13 C­{ 1 H} NMR (100 MHz, DMSO-d 6); δ = 157.18 (d, J = 4 Hz), 154.16 (d, J = 6), 143.97 (ArC–H), 143.62 (ArC–H), 142.96 (ArC–H), 142.65 (d, J = 10) (ArC–H), 120.96 (ArC–H), 120.19 (ArC–H), 119.46 (ArC–H), 117.96 (ArC–H), 117.45 (ArC–H), 63.70 (d, J = 13 Hz carboraneC–P), 60.68 (d, J = 10 Hz carboraneC–P) ppm. 31 P NMR (162 MHz, DMSO-d 6); δ = 24.1 ppm. 11 B NMR (128 MHz, DMSO-d 6); δ = −32.3 to 20.5 (br) ppm. HRMS for [M – B+ ] (APCI negative mode): Calc. for C14 H28 10B3 11B15 N2 P S = 482.3495; found = 482.3493.

X-ray Crystallography Details

The crystals for all the compounds herein were mounted on a cryoloop with Paratone oil, and all data were collected at 100(2) or 110(2) K (for L’LP). Single crystal X-ray diffraction data for LPCl 2 , L 2 P + , L­(L nido )­P + , LH 2 + were collected on a Rigaku Oxford Diffraction - XtaLAB Synergy-S diffractometer operated with monochromated MoKα (α = 0.71073 Å) or CuKα (for L2P+, LH2 +; α = 1.54184 Å) X-ray source, respectively. The data collection, cell refinement, data reduction, and analytical method absorption correction were performed using CrysAlisPro. Single crystal X-ray diffraction data for L’LP were collected on a Bruker D8 KAPPA APEXDuo diffractometer equipped with an APEX II CCD detector using a TRIUMPH monochromator with a MoKα X-ray source (α = 0.71073 Å). Unit cell determination, refinement, and data collection were done using the Bruker APEX-III suite, data reduction and integration were performed using SAINT v8.34A (Bruker, 2013) and absorption corrections and scaling were done using SADABS-2014/5 (Bruker,2014/5). All the crystal structures were solved through OLEX2 package using SHELXT and the structures were refined using SHELXL. All non-hydrogen atoms were refined anisotropically. All the figures were generated using Mercury 3.0.

DFT Computational Details

DFT calculations were performed using Gaussian 09.2. Geometry optimization of all the molecules was carried out using the B3LYP-D3­(BJ)/6–311++G­(d,p) , and BP86-D3­(BJ)/def2-TZVP implemented in the Gaussian 09 software. Conductor-like polarizable continuum model (CPCM) was used to account for the effect of chloroform. Thermal energy corrections were extracted from the results of frequency analysis performed at the same level of theory. Frequency analysis of all the molecules and intermediates contained no imaginary frequency, showing that these are energy minima. AIM analysis was performed using Multiwfn. The computational pictures were generated using Avogadro.

Supplementary Material

ic6c01373_si_001.pdf (6.3MB, pdf)

Acknowledgments

This work was supported by the Israeli Science Foundation, Grant 195/22, and the Israel Ministry of Science Technology & Space, Grant 01032376. We acknowledge Mr. Kham Lek Chaton for the help with the DFT computations.

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.inorgchem.6c01373.

  • NMR spectra (PDF)

The authors declare no competing financial interest.

Published as part of Inorganic Chemistry special issue “Current Advancements in Main Group Chemistry”.

References

  1. a Crabtree, R. H. The Organometallic Chemistry of the Transition Metals, 6th ed.; Wiley-VCH: Hoboken, NJ, 2014. [Google Scholar]; b Cornils, B. ; Herrmann, W. A. . Applied Homogeneous Catalysis with Organometallic Compounds; Wiley-VCH: Weinheim, 2002. [Google Scholar]; c Docherty J. H., Lister T. M., Mcarthur G., Findlay M. T., Domingo-Legarda P., Kenyon J., Choudhary S., Larrosa I.. Transition-Metal-Catalyzed C–H Bond Activation for the Formation of C–C Bonds in Complex Molecules. Chem. Rev. 2023;123(12):7692–7760. doi: 10.1021/acs.chemrev.2c00888. [DOI] [PMC free article] [PubMed] [Google Scholar]; d Beletskaya I. P., Ananikov V. P.. Transition-Metal-Catalyzed C–S, C–Se, and C–Te Bond Formations via Cross-Coupling and Atom-Economic Addition Reactions. Achievements and Challenges. Chem. Rev. 2022;122(21):16110–16293. doi: 10.1021/acs.chemrev.1c00836. [DOI] [PubMed] [Google Scholar]; e Alig L., Fritz M., Schneider S.. First-Row Transition Metal (De)­Hydrogenation Catalysis Based On Functional Pincer Ligands. Chem. Rev. 2019;119(4):2681–2751. doi: 10.1021/acs.chemrev.8b00555. [DOI] [PubMed] [Google Scholar]
  2. a Power P. P.. Main-Group Elements as Transition Metals. Nature. 2010;463(7278):171–177. doi: 10.1038/nature08634. [DOI] [PubMed] [Google Scholar]; b Melen R. L.. Frontiers in Molecular P-Block Chemistry: From Structure to Reactivity. Science. 2019;363(6426):479–484. doi: 10.1126/science.aau5105. [DOI] [PubMed] [Google Scholar]
  3. a Chu T., Nikonov G. I.. Oxidative Addition and Reductive Elimination at Main-Group Element Centers. Chem. Rev. 2018;118(7):3608–3680. doi: 10.1021/acs.chemrev.7b00572. [DOI] [PubMed] [Google Scholar]; b Weetman C., Inoue S.. The Road Travelled: After Main-Group Elements as Transition Metals. ChemCatChem. 2018;10(19):4213–4228. doi: 10.1002/cctc.201800963. [DOI] [Google Scholar]
  4. a Martin D., Soleilhavoup M., Bertrand G.. Stable Singlet Carbenes as Mimics for Transition Metal Centers. Chem. Sci. 2011;2(3):389–399. doi: 10.1039/C0SC00388C. [DOI] [PMC free article] [PubMed] [Google Scholar]; b Frey G. D., Lavallo V., Donnadieu B., Schoeller W. W., Bertrand G.. Facile Splitting of Hydrogen and Ammonia by Nucleophilic Activation at a Single Carbon Center. Science. 2007;316:439–441. doi: 10.1126/science.1141474. [DOI] [PubMed] [Google Scholar]; c Nesterov V., Reiter D., Bag P., Frisch P., Holzner R., Porzelt A., Inoue S.. NHCs in Main Group Chemistry. Chem. Rev. 2018;118(19):9678–9842. doi: 10.1021/acs.chemrev.8b00079. [DOI] [PubMed] [Google Scholar]
  5. a Légaré M.-A., Bélanger-Chabot G., Dewhurst R. D., Welz E., Krummenacher I., Engels B., Braunschweig H.. Nitrogen fixation and reduction at boron. Science. 2018;359:896–900. doi: 10.1126/science.aaq1684. [DOI] [PubMed] [Google Scholar]; b Dahcheh F., Martin D., Stephan D. W., Bertrand G.. Synthesis and Reactivity of a CAAC-Aminoborylene Adduct: A Hetero-Allene or an Organoboron Isoelectronic with Singlet Carbenes. Angew. Chem., Int. Ed. 2014;53(48):13159–13163. doi: 10.1002/anie.201408371. [DOI] [PubMed] [Google Scholar]; c Soleilhavoup M., Bertrand G.. Borylenes: An Emerging Class of Compounds. Angew. Chem., Int. Ed. 2017;56(35):10282–10292. doi: 10.1002/anie.201705153. [DOI] [PubMed] [Google Scholar]; d Légaré M.-A., Pranckevicius C., Braunschweig H.. Metallomimetic Chemistry of Boron. Chem. Rev. 2019;119(14):8231–8261. doi: 10.1021/acs.chemrev.8b00561. [DOI] [PubMed] [Google Scholar]
  6. a Hicks J., Vasko P., Goicoechea J. M., Aldridge S.. Synthesis, Structure and Reaction Chemistry of a Nucleophilic Aluminyl Anion. Nature. 2018;557(7703):92–95. doi: 10.1038/s41586-018-0037-y. [DOI] [PubMed] [Google Scholar]; b Hicks J., Vasko P., Goicoechea J. M., Aldridge S.. The Aluminyl Anion: A New Generation of Aluminium Nucleophile. Angew. Chem., Int. Ed. 2021;60(4):1702–1713. doi: 10.1002/anie.202007530. [DOI] [PubMed] [Google Scholar]; c Protchenko A. V., Birjkumar K. H., Dange D., Schwarz A. D., Vidovic D., Jones C., Kaltsoyannis N., Mountford P., Aldridge S.. A Stable Two-Coordinate Acyclic Silylene. J. Am. Chem. Soc. 2012;134(15):6500–6503. doi: 10.1021/ja301042u. [DOI] [PubMed] [Google Scholar]; d Spikes G. H., Fettinger J. C., Power P. P.. Facile Activation of Dihydrogen by an Unsaturated Heavier Main Group Compound. J. Am. Chem. Soc. 2005;127(35):12232–12233. doi: 10.1021/ja053247a. [DOI] [PubMed] [Google Scholar]; e Peng Y., Ellis B. D., Wang X., Power P. P.. Diarylstannylene Activation of Hydrogen or Ammonia with Arene Elimination. J. Am. Chem. Soc. 2008;130(37):12268–12269. doi: 10.1021/ja805358u. [DOI] [PubMed] [Google Scholar]
  7. a Stephan D. W.. Frustrated Lewis Pairs: From Concept to Catalysis. Acc. Chem. Res. 2015;48(2):306–316. doi: 10.1021/ar500375j. [DOI] [PubMed] [Google Scholar]; b Stephan D. W.. The broadening reach of frustrated Lewis pair chemistry. Science. 2016;354:aaf7229. doi: 10.1126/science.aaf7229. [DOI] [PubMed] [Google Scholar]
  8. a Hannah T. J., Chitnis S. S.. Ligand-Enforced Geometric Constraints and Associated Reactivity in p-Block Compounds. Chem. Soc. Rev. 2024;53(2):764–792. doi: 10.1039/D3CS00765K. [DOI] [PubMed] [Google Scholar]; b Lipshultz J. M., Li G., Radosevich A. T.. Main Group Redox Catalysis of Organopnictogens: Vertical Periodic Trends and Emerging Opportunities in Group 15. J. Am. Chem. Soc. 2021;143(4):1699–1721. doi: 10.1021/jacs.0c12816. [DOI] [PMC free article] [PubMed] [Google Scholar]; c Abbenseth J., Goicoechea J. M.. Recent Developments in the Chemistry of Non-Trigonal Pnictogen Pincer Compounds: From Bonding to Catalysis. Chem. Sci. 2020;11(36):9728–9740. doi: 10.1039/D0SC03819A. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. a Bonfante S., Lorber C., Lynam J. M., Simonneau A., Slattery J. M.. Metallomimetic C–F Activation Catalysis by Simple Phosphines. J. Am. Chem. Soc. 2024;146(3):2005–2014. doi: 10.1021/jacs.3c10614. [DOI] [PMC free article] [PubMed] [Google Scholar]; b Fujimoto H., Kodama T., Yamanaka M., Tobisu M.. Phosphine-Catalyzed Intermolecular Acylfluorination of Alkynes via a P­(V) Intermediate. J. Am. Chem. Soc. 2020;142(41):17323–17328. doi: 10.1021/jacs.0c08928. [DOI] [PubMed] [Google Scholar]; c Xie C., Smaligo A. J., Song X.-R., Kwon O.. Phosphorus-Based Catalysis. ACS Cent. Sci. 2021;7(4):536–558. doi: 10.1021/acscentsci.0c01493. [DOI] [PMC free article] [PubMed] [Google Scholar]; d Fujimoto H., Yasui K., Tobisu M.. Non-Classical Molecular Activation by Phosphines and N-Heterocyclic Carbenes and Its Application to Catalytic Reactions. Bull. Chem. Soc. Jpn. 2023;96(9):872–886. doi: 10.1246/bcsj.20230150. [DOI] [Google Scholar]; e Š imon P., Jambor R., Růzič ka ˇ A., Dostál L.. Oxidative Addition of Diphenyldichalcogenides PhEEPh (E = S, Se, Te) to Low-Valent CN- and NCN-Chelated Organoantimony and Organobismuth Compounds. Organometallics. 2013;32(1):239–248. doi: 10.1021/om3010383. [DOI] [Google Scholar]; f Ganesamoorthy C., Wölper C., Dostál L., Schulz S.. Syntheses and Structures of N,C,N-Stabilized Antimony Chalcogenides. J. Organomet. Chem. 2017;845:38–43. doi: 10.1016/j.jorganchem.2017.01.007. [DOI] [Google Scholar]; g Moon H. W., Cornella J.. Bismuth Redox Catalysis: An Emerging Main-Group Platform for Organic Synthesis. ACS Catal. 2022;12(2):1382–1393. doi: 10.1021/acscatal.1c04897. [DOI] [PMC free article] [PubMed] [Google Scholar]; h Mato M., Cornella J.. Bismuth in Radical Chemistry and Catalysis. Angew. Chem., Int. Ed. 2024;63(8):e202315046. doi: 10.1002/anie.202315046. [DOI] [PubMed] [Google Scholar]
  10. a Lin Y.-C., Hatzakis E., McCarthy S. M., Reichl K. D., Lai T.-Y., Yennawar H. P., Radosevich A. T.. P–N Cooperative Borane Activation and Catalytic Hydroboration by a Distorted Phosphorous Triamide Platform. J. Am. Chem. Soc. 2017;139(16):6008–6016. doi: 10.1021/jacs.7b02512. [DOI] [PMC free article] [PubMed] [Google Scholar]; b Dunn N. L., Ha M., Radosevich A. T.. Main Group Redox Catalysis: Reversible PIII/PV Redox Cycling at a Phosphorus Platform. J. Am. Chem. Soc. 2012;134(28):11330–11333. doi: 10.1021/ja302963p. [DOI] [PubMed] [Google Scholar]
  11. a Bawari D., Toami D., Dobrovetsky R.. Advancing Metallomimetic Catalysis through Structural Constraints of Cationic PIII Species. Chem. Commun. 2025;61(32):5871–5882. doi: 10.1039/D5CC00723B. [DOI] [PubMed] [Google Scholar]; b Volodarsky S., Dobrovetsky R.. Ambiphilic Geometrically Constrained Phosphenium Cation. Chem. Commun. 2018;54(50):6931–6934. doi: 10.1039/C8CC02423E. [DOI] [PubMed] [Google Scholar]; c Bawari D., Malahov I., Dobrovetsky R.. Sb-to-P Metathesis: A Direct Route to Structurally Constrained, Cationic PIII Compound. Angew. Chem., Int. Ed. 2025;64(7):e202419772. doi: 10.1002/anie.202419772. [DOI] [PubMed] [Google Scholar]
  12. a Volodarsky S., Bawari D., Dobrovetsky R.. Dual Reactivity of a Geometrically Constrained Phosphenium Cation. Angew. Chem., Int. Ed. 2022;61(36):e202208401. doi: 10.1002/anie.202208401. [DOI] [PMC free article] [PubMed] [Google Scholar]; b Chulsky K., Malahov I., Bawari D., Dobrovetsky R.. Metallomimetic Chemistry of a Cationic, Geometrically Constrained Phosphine in the Catalytic Hydrodefluorination and Amination of Ar–F Bonds. J. Am. Chem. Soc. 2023;145(6):3786–3794. doi: 10.1021/jacs.2c13318. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. a Roth D., Radosevich A. T., Greb L.. Reversible Oxidative Addition of Nonactivated C–H Bonds to Structurally Constrained Phosphenium Ions. J. Am. Chem. Soc. 2023;145(44):24184–24190. doi: 10.1021/jacs.3c08456. [DOI] [PMC free article] [PubMed] [Google Scholar]; b You L., Roth D., Greb L.. Structural Constraint at a P–P Bond: Phosphinophosphination of Alkenes, Alkynes, and Carbonyls by a Concerted Mechanism. Chem. Sci. 2025;16(4):1716–1721. doi: 10.1039/D4SC06581F. [DOI] [PMC free article] [PubMed] [Google Scholar]; c Dube J. W., Macdonald C. L. B., Ragogna P. J.. Accessing the Coordination Chemistry of Phosphorus­(I) Zwitterions. Angew. Chem., Int. Ed. 2012;51:13026–13030. doi: 10.1002/anie.201205744. [DOI] [PubMed] [Google Scholar]; d Liu Q., Zhou J., Zhang S.. Zwitterionic Phosphorus­(I) Compounds Supported by a Bis­(Carbene)­Borate: Synthesis, Protonation, and Thermodynamics of P–H Bonds. Inorg. Chem. 2026;65:6049–6059. doi: 10.1021/acs.inorgchem.5c05780. [DOI] [PubMed] [Google Scholar]
  14. Liu Y., Dong W., Li Z. H., Wang H.. Methane Activation by a Borenium Complex. Chem. 2021;7(7):1843–1851. doi: 10.1016/j.chempr.2021.03.010. [DOI] [Google Scholar]
  15. a Akram M. O., Tidwell J. R., Dutton J. L., Martin C. D.. Tris­(ortho-Carboranyl)­Borane: An Isolable, Halogen-Free, Lewis Superacid. Angew. Chem., Int. Ed. 2022;61(46):e202212073. doi: 10.1002/anie.202212073. [DOI] [PMC free article] [PubMed] [Google Scholar]; b Akram M. O., French K. A., Shuford K. L., Martin C. D.. A Crystalline Boravinylidene from an Arrested Hydroboration Reaction. J. Am. Chem. Soc. 2025;147(36):33120–33126. doi: 10.1021/jacs.5c11053. [DOI] [PubMed] [Google Scholar]
  16. a Zhang C., Wang J., Su W., Lin Z., Ye Q.. Synthesis, Characterization, and Density Functional Theory Studies of Three-Dimensional Inorganic Analogues of 9,10-DiboraanthraceneA New Class of Lewis Superacids. J. Am. Chem. Soc. 2021;143(23):8552–8558. doi: 10.1021/jacs.1c03057. [DOI] [PubMed] [Google Scholar]; b Diab M., Jaiswal K., Bawari D., Dobrovetsky R.. The Chemistry of [1,1′-bis­(o-Carboranyl)]­Borane η2 -σ-Silane Adduct. Isr. J. Chem. 2023;63:e202300010 [Google Scholar]
  17. a Humphries A. L., Tellier G. A., Smith M. D., Chianese A. R., Peryshkov D. V.. N–H Bond Activation of Ammonia by a Redox-Active Carboranyl Diphosphine. J. Am. Chem. Soc. 2024;146(48):33159–33168. doi: 10.1021/jacs.4c12146. [DOI] [PubMed] [Google Scholar]; b Riffle J. R., Jowers C. L., Luna S., Smith M. D., Peryshkov D. V.. Non-Spectator Behavior of a Neutral Phosphine Ligand Driven by a Redox-Active Boron Cluster. Chem. Sci. 2025;16(35):15997–16003. doi: 10.1039/D5SC04058B. [DOI] [PMC free article] [PubMed] [Google Scholar]
  18. a.Sceney M., White K. F., Dutton J. L.. Ortho-Carborane-Supported Hypervalent Iodine­(III) Reagents: A Scaffold for Enhanced Oxidative Capability. J. Am. Chem. Soc. 2025;147(36):32347–32351. doi: 10.1021/jacs.5c10358. [DOI] [PubMed] [Google Scholar]
  19. Bawari D., Toami D., Jaiswal K., Dobrovetsky R.. Hydrogen Splitting at a Single Phosphorus Center and Its Use for Hydrogenation. Nat. Chem. 2024;16(8):1261–1266. doi: 10.1038/s41557-024-01569-y. [DOI] [PubMed] [Google Scholar]
  20. Anderson K. P., Mills H. A., Mao C., Kirlikovali K. O., Axtell J. C., Rheingold A. L., Spokoyny A. M.. Improved Synthesis of Icosahedral Carboranes Containing Exopolyhedral B C and C C Bonds. Tetrahedron. 2019;75(2):187–191. doi: 10.1016/j.tet.2018.11.040. [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. Deposition Numbers 2512627; 2512628; 2512629; 2512630; 2512631; 2512661 contain the supplementary crystallographic data for this paper. These data are provided free of charge by the joint Cambridge Crystallographic Data Center and Fachinformationszentrum Karlsruhe Access Structures service.
  22. a Lamande′ L., Munoz A.. Stabilisation de cations oxophosphenium par liaisons datives P←N. Tetrahedron Lett. 1991;32:75–78. doi: 10.1016/S0040-4039(00)71222-6. [DOI] [Google Scholar]; b Pipko S. E., Balitzky Y. V., Sinitsa A. D., Gololobov Y. G.. Peculiarities of Structure and Properties of Phosphorus-Containing Cations with Two Intramolecular Donor-Acceptor Bonds N→P. Synthesis of the First 5-Coordinated P-Cation with P–N Bond. Tetrahedron Lett. 1994;35(1):165–168. doi: 10.1016/0040-4039(94)88191-X. [DOI] [Google Scholar]; c Carré F., Chuit C., Corriu R. J. P., Mehdi A., Reyé C.. N → P Intramolecular Stabilization of Phosphenium Ions and Preparation of Hypercoordinated Phosphanes with Unusual Properties. J. Organomet. Chem. 1997;529:59–68. doi: 10.1016/S0022-328X(96)06659-4. [DOI] [Google Scholar]; d Ellis B. D., Ragogna P. J., Macdonald C. L. B.. Computational Insights into the Acceptor Chemistry of Phosphenium Cations. Inorg. Chem. 2004;43:7857–7867. doi: 10.1021/ic0488738. [DOI] [PubMed] [Google Scholar]; e Karsch H. H., Witt E., Hahn F. E.. A Triphosphete and a Spirocyclic Cation with a PP4 Skeleton and a 10e Spiro P Atom. Angew. Chem., Int. Ed. 1996;35:2242–2244. doi: 10.1002/anie.199622421. [DOI] [Google Scholar]; f Kilian P., Slawin A. M. Z.. 1,8,9-Substituted Anthracenes, Intramolecular Phosphine Donor Stabilized Metaphosphonate and Phosphenium. Dalton Trans. 2007;30:3289–3296. doi: 10.1039/b705286c. [DOI] [PubMed] [Google Scholar]; g Clark E. R., Borys A. M., Pearce K.. Donor-Substituted Phosphanes – Surprisingly Weak Lewis Donors for Phosphenium Cation Stabilisation. Dalton Trans. 2016;45:16125–16129. doi: 10.1039/C6DT03478K. [DOI] [PubMed] [Google Scholar]; h Zhang T., Lee V. Y., Morisako S., Aoyagi S., Sasamori T.. Ferrocene-Based Phosphenium Ion with Intramolecular Phosphine Coordination. Eur. J. Inorg. Chem. 2021;2021:3988–3991. doi: 10.1002/ejic.202100615. [DOI] [Google Scholar]; i Franz R., Bartek M., Bruhn C., Kelemen Z., Pietschnig R.. P+ Addition and Transfer Involving a Tetraphosphenium Ion. Chem. Sci. 2024;16:139–146. doi: 10.1039/D4SC06823H. [DOI] [PMC free article] [PubMed] [Google Scholar]
  23. a Becke A. D.. Density-Functional Thermochemistry. III. The Role of Exact Exchange. J. Chem. Phys. 1993;98:5648–5652. doi: 10.1063/1.464913. [DOI] [Google Scholar]; b Lee C., Yang W., Parr R. G.. Development of the Colle-Salvetti Correlation-Energy Formula into a Functional of the Electron Density. Phys. Rev. B. 1988;37(2):785–789. doi: 10.1103/PhysRevB.37.785. [DOI] [PubMed] [Google Scholar]; c Grimme S., Antony J., Ehrlich S., Krieg H.. A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu. J. Chem. Phys. 2010;132:154104. doi: 10.1063/1.3382344. [DOI] [PubMed] [Google Scholar]; d Grimme S., Ehrlich S., Goerigk L.. Effect of the Damping Function in Dispersion Corrected Density Functional Theory. J. Comput. Chem. 2011;32(7):1456–1465. doi: 10.1002/jcc.21759. [DOI] [PubMed] [Google Scholar]
  24. a Krishnan R., Binkley J. S., Seeger R., Pople J. A.. Self-Consistent Molecular Orbital Methods. XX. A Basis Set for Correlated Wave Functions. J. Chem. Phys. 1980;72(1):650–654. doi: 10.1063/1.438955. [DOI] [Google Scholar]; b Hariharan P. C., Pople J. A.. The Influence of Polarization Functions on Molecular Orbital Hydrogenation Energies. Theor. Chim. Acta. 1973;28(3):213–222. doi: 10.1007/BF00533485. [DOI] [Google Scholar]; c Francl M. M., Pietro W. J., Hehre W. J., Binkley J. S., Gordon M. S., DeFrees D. J., Pople J. A.. Self-Consistent Molecular Orbital Methods. XXIII. A Polarization-Type Basis Set for Second-Row Elements. J. Chem. Phys. 1982;77(7):3654–3665. doi: 10.1063/1.444267. [DOI] [Google Scholar]
  25. a Wiberg K. B., Pfeiffer J. G.. Orbital Factors in Cyclobutyl Solvolyses. J. Am. Chem. Soc. 1968;90(19):5324–5325. doi: 10.1021/ja01021a077. [DOI] [Google Scholar]; b Glendening, E. D. ; Badenhoop, J. K. ; Reed, A. E. ; Carpenter, J. E. ; Bohmann, J. A. ; Morales, C. M. ; Weinhold, F. . NBO 6.0; Theoretical Chemistry Institute, University of Wisconsin: Madison, WI, 2013. [Google Scholar]
  26. Bader, R. F. W. Atoms in Molecules: A Quantum Theory; Clarendon Press: Oxford, 1994. [Google Scholar]
  27. a Li C., Wang Q., Zhang J.-Q., Ye J., Xie J., Xu Q., Han L.-B.. Water Determines the Products: An Unexpected Bro̷nsted Acid-Catalyzed PO–R Cleavage of P­(III) Esters Selectively Producing P­(O)–H and P­(O)–R Compounds. Green Chem. 2019;21(11):2916–2922. doi: 10.1039/C9GC01254K. [DOI] [Google Scholar]; b Plutnar J., Sofer Z., Pumera M.. Products of Degradation of Black Phosphorus in Protic Solvents. ACS Nano. 2018;12(8):8390–8396. doi: 10.1021/acsnano.8b03740. [DOI] [PubMed] [Google Scholar]
  28. a Inoue A., Shinokubo H., Oshima K.. Oxidative Heck-Type Reaction Involving Cleavage of a Carbon–Phosphorus Bond of Arylphosphonic Acids. J. Am. Chem. Soc. 2003;125(6):1484–1485. doi: 10.1021/ja026758v. [DOI] [PubMed] [Google Scholar]; b Garrou P. E.. Transition-Metal-Mediated Phosphorus-Carbon Bond Cleavage and Its Relevance to Homogeneous Catalyst Deactivation. Chem. Rev. 1985;85(3):171–185. doi: 10.1021/cr00067a001. [DOI] [Google Scholar]; c Budzelaar P. H. M., van Doorn J. A., Meijboom N. R.. Reductive Cleavage of the Carbon–Phosphorus Bond with Alkali Metals. I. Cleavage of Functionalised Triphenylphosphines; Formation of Secondary and Primary Phosphines. Trav. Chim. Pays-Bas. 1991;110:420–432. doi: 10.1002/recl.19911101006. [DOI] [Google Scholar]; d Shephard A. C. G., Daniels D. P., Deacon G. B., Guo Z., Jaroschik F., Junk P. C.. Selective Carbon-Phosphorus Bond Cleavage: Expanding the Toolbox for Accessing Bulky Divalent Lanthanoid Sandwich Complexes. Chem. Commun. 2022;58(27):4344–4347. doi: 10.1039/D2CC00698G. [DOI] [PubMed] [Google Scholar]
  29. a Hudson R. F., Moss G.. The mechanism of hydrolysis of phosphorochloridates and related compounds. Part IV. Phosphoryl chloride. J. Chem. Soc. 1962:3599–3604. doi: 10.1039/jr9620003599. [DOI] [Google Scholar]; b Delley R. J., O’Donoghue A. C., Hodgson D. R. W.. Hydrolysis Studies of Phosphodichloridate and Thiophosphodichloridate Ions. J. Org. Chem. 2012;77(13):5829–5831. doi: 10.1021/jo300808m. [DOI] [PubMed] [Google Scholar]
  30. Notably, the P–N bonds are also known to react with water and alcohols, see for example:; Gopalakrishnan J.. Aminophosphines: Their Chemistry and Role as Ligands and Synthons. Appl. Organometal. Chem. 2009;23(8):291–318. doi: 10.1002/aoc.1515. [DOI] [Google Scholar]
  31. Oberdorfer R., Nieger M., Niecke E.. 1,3-Diaza-2λ2-phosphonia-4λ4-gallatacyclobutane. Chem. Ber. 1994;127:2397–2401. doi: 10.1002/cber.19941271210. [DOI] [Google Scholar]
  32. a Willans C. E., Kilner C. A., Fox M. A.. Deboronation and Deprotonation of ortho-Carborane with N-Heterocyclic Carbenes. Chem.Eur. J. 2010;16(35):10644–10648. doi: 10.1002/chem.201001730. [DOI] [PubMed] [Google Scholar]; b Fox M. A., Wade K.. Deboronation of 9-Substituted-Ortho- and -Meta-Carboranes. J. Organomet. Chem. 1999;573(1–2):279–291. doi: 10.1016/S0022-328X(98)00881-X. [DOI] [Google Scholar]; c Genady A. R., Tan J., El-Zaria M. E., Zlitni A., Janzen N., Valliant J. F.. Synthesis, characterization and radiolabeling of carboranefunctionalized tetrazines for use in inverse electron demand DielseAlder ligation reactions. J. Organomet. Chem. 2015;791:204–213. doi: 10.1016/j.jorganchem.2015.05.033. [DOI] [Google Scholar]; d Zheng F., Xie Z.. Reaction of O-Carboranes with Sterically Demanding N-Heterocyclic Carbene: Synthesis and Structural Characterization of 1:1 Adducts. Dalton Trans. 2012;41(41):12907. doi: 10.1039/c2dt31765f. [DOI] [PubMed] [Google Scholar]
  33. For details on the fate of the decapitated B vertex, see the ESI and the following references:; a Taoda Y., Sawabe T., Endo Y., Yamaguchi K., Fujii S., Kagechika H.. Identification of an Intermediate in the Deboronation of Ortho-Carborane: An Adduct of Ortho-Carborane with Two Nucleophiles on One Boron Atom. Chem. Commun. 2008;17:2049–2051. doi: 10.1039/b716079h. [DOI] [PubMed] [Google Scholar]; b Davidson M. G., Fox M. A., Hibbert T. G., Howard J. A. K., Mackinnon A., Neretin I. S., Wade K.. Deboronation of Ortho-Carborane by an Iminophosphorane: Crystal Structures of the Novel Carborane Adduct Nido-C2B10H12·HNP­(NMe2)3 and the Borenium Salt [(Me2N)3PNHBNP­(NMe2)3]2O2 +(C2B9H12 –)2 . Chem. Commun. 1999;17:1649–1650. doi: 10.1039/a903030a. [DOI] [Google Scholar]
  34. Grimes, R. N. Carboranes, 2nd ed.; Academic Press: London, 2011. [Google Scholar]
  35. a Han Z.-Z., Zhang C.-P.. Phenyl­(Trifluoroethyl)­Iodonium-Triflate-Initiated Ring-Opening Polymerization of Tetrahydrofuran. Tetrahedron Lett. 2021;73:153146. doi: 10.1016/j.tetlet.2021.153146. [DOI] [Google Scholar]; b Yoshida E., Sugita A.. Synthesis of Poly­(Tetrahydrofuran) with a Nitroxyl Radical at the Chain End and Its Application to Living Radical Polymerization. Macromolecules. 1996;29(20):6422–6426. doi: 10.1021/ma9605210. [DOI] [Google Scholar]
  36. Pérez M., Hounjet L. J., Caputo C. B., Dobrovetsky R., Stephan D. W.. Olefin Isomerization and Hydrosilylation Catalysis by Lewis Acidic Organofluorophosphonium Salts. J. Am. Chem. Soc. 2013;135(49):18308–18310. doi: 10.1021/ja410379x. [DOI] [PubMed] [Google Scholar]
  37. Rawat S., Bhandari M., Prashanth B., Singh S.. Three Coordinated Organoaluminum Cation for Rapid and Selective Cyanosilylation of Carbonyls under Solvent-Free Conditions. ChemCatChem. 2020;12(9):2407–2411. doi: 10.1002/cctc.202000309. [DOI] [Google Scholar]
  38. a Hu C., Pink M., Goicoechea J. M.. Isolation of a Phosphinidene Sulfide and Selenide. Chem. Sci. 2025;16(32):14690–14697. doi: 10.1039/D5SC04352B. [DOI] [PMC free article] [PubMed] [Google Scholar]; b Li X., Chen Y., Zhang Y., Xu L., Tan G.. Isolable Arylphosphinidene Chalcogenides and their Radical Anions. Angew. Chem., Int. Ed. 2025;64(42):e202514521. doi: 10.1002/anie.202514521. [DOI] [PubMed] [Google Scholar]; c Bawari D., Prashanth B., Ravi S., Shamasundar K. R., Singh S., Wright D. S.. Two Different Pathways in the Reduction of [(S = )­PCl­(μ-Nt Bu)]2 with Na. Chem.Eur. J. 2016;22(34):12027–12033. doi: 10.1002/chem.201600839. [DOI] [PubMed] [Google Scholar]
  39. a Adenot A., von Wolff N., Lefevre ` G., Berthet J.-C., Thuéry P., Cantat T.. Activation of SO2 by N/Si+ and N/B Frustrated Lewis Pairs: Experimental and Theoretical Comparison with CO2 Activation. Chem.Eur. J. 2019;25(34):8118–8126. doi: 10.1002/chem.201901088. [DOI] [PubMed] [Google Scholar]; b Emmett E. J., Willis M. C.. The Development and Application of Sulfur Dioxide Surrogates in Synthetic Organic Chemistry. Asian J. Org. Chem. 2015;4(7):602–611. doi: 10.1002/ajoc.201500103. [DOI] [Google Scholar]
  40. a Bruker (2019). APEX ΙΙΙ. Bruker AXS Inc.: Madison, Wisconsin, USA. [Google Scholar]; b Bruker (2013). SAINT v8.34A. Bruker AXS Inc.,: Madison, Wisconsin, USA.. [Google Scholar]; c Bruker (2014/5). Sadabs, 2014/5. Bruker AXS Inc.: Madison, Wisconsin, USA. [Google Scholar]
  41. a Dolomanov O. V., Bourhis L. J., Gildea R. J., Howard J. A. K., Puschmann H.. OLEX2: A Complete Structure Solution, Refinement and Analysis Program. J. Appl. Crystallogr. 2009;42:339–341. doi: 10.1107/S0021889808042726. [DOI] [Google Scholar]; b Sheldrick G. M.. SHELXT–Integrated space-group and crystal-structure determination. Acta Cryst. A. 2015;71:3–8. doi: 10.1107/S2053229614024218. [DOI] [PMC free article] [PubMed] [Google Scholar]; c Sheldrick G. M.. Crystal structure refinement with SHELXL. Acta Cryst. A. 2015;71:3–8. doi: 10.1107/S2053229614024218. [DOI] [PMC free article] [PubMed] [Google Scholar]
  42. Gaussian 09, Revision D.01, M. J., Frisch , G. W., Trucks , H. B., Schlegel , G. E., Scuseria , M. A., Robb , J. R., Cheeseman , G., Scalmani , V., Barone , B., Mennucci , G. A., Petersson , H., Nakatsuji , M., Caricato , X., Li , H. P., Hratchian , A. F., Izmaylov , J., Bloino , G., Zheng , J. L., Sonnengerg , M., Hada , M., Ehara , K., Toyota , R., Fukuda , J., Hasegawa , M., Ishida , T., Nakajima , Y., Honda , O., Kitao , H., Nakai , T., Vreven , J. A., Montgomery, Jr. , J. E., Peralta , F., Ogliaro , M., Bearpark , J. J., Heyd , E., Brothers , K. N., Kudin , V. N., Staroverov , T., Keith , R., Kobayashi , J., Normand , K., Raghavachari , A., Rendell , J. C., Burant , S. S., Iyengar , J., Tomasi , M., Cossi , N., Rega , N. J., Millam , M., Klene , J. E., Knox , J. B., Cross , V., Bakken , C., Adamo , J., Jaramillo , R., Gomperts , R. E., Stratmann , O., Yazyev , A. J., Austin , R., Cammi , C., Pomelli , J. W., Ochterski , R. L., Martin , K., Morokuma , V. G., Zakrzewski , G. A., Voth , P., Salvador , J. J., Dannenberg , S., Dapprich , A. D., Daniels , Ö., Farkas , J. B., Foresman , J. V., Ortiz , J., Cioslowski ; D. J., Fox , Gaussian, Inc.: Wallingford CT, 2010. [Google Scholar]
  43. a Becke A. D.. Density-functional exchange-energy approximation with correct asymptotic behavior. Phys. Rev. A. 1988;38:3098–3100. doi: 10.1103/PhysRevA.38.3098. [DOI] [PubMed] [Google Scholar]; b Perdew J. P.. Density-functional approximation for the correlation energy of the inhomogeneous electron gas. Phys. Rev. B. 1986;34:8822–8824. doi: 10.1103/PhysRevB.33.8822. [DOI] [PubMed] [Google Scholar]; c Weigend F., Ahlrichs R.. Balanced basis sets of split valence, triple zeta valence and quadruple zeta valence quality for H to Rn: Design and assessment of accuracy. Phys. Chem. Chem. Phys. 2005;7:3297–3305. doi: 10.1039/b508541a. [DOI] [PubMed] [Google Scholar]
  44. a Barone V., Cossi M.. Quantum Calculation of Molecular Energies and Energy Gradients in Solution by a Conductor Solvent Model. J. Phys. Chem. A. 1998;102:1995–2001. doi: 10.1021/jp9716997. [DOI] [Google Scholar]; b Cossi M., Rega N., Scalmani G., Barone V.. Energies, structures, and electronic properties of molecules in solution with the C-PCM solvation model. J. Comput. Chem. 2003;24:669–681. doi: 10.1002/jcc.10189. [DOI] [PubMed] [Google Scholar]
  45. a.Lu T., Chen F.. Multiwfn: A Multifunctional Wavefunction Analyzer. J. Comput. Chem. 2012;33:580–592. doi: 10.1002/jcc.22885. [DOI] [PubMed] [Google Scholar]
  46. Hanwell M. D., Curtis D. E., Lonie D. C., Vandermeersch T., Zurek E., Hutchison G. R.. Avogadro: An advanced semantic chemical editor, visualization, and analysis platform. J. Cheminform. 2012;4:17. doi: 10.1186/1758-2946-4-17. [DOI] [PMC free article] [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

ic6c01373_si_001.pdf (6.3MB, pdf)

Articles from Inorganic Chemistry are provided here courtesy of American Chemical Society

RESOURCES