Indirect Access to Carbene Adducts of Bismuth- and Antimony-Substituted Phosphaketene and Their Unusual Thermal Transformation to Dipnictines and [(NHC)₂OCP][OCP]

Abstract

The synthesis and thermal redox chemistry of the first antimony (Sb)– and bismuth (Bi)–phosphaketene adducts are described. When diphenylpnictogen chloride [Ph 2 PnCl (Pn = Sb or Bi)] is reacted with sodium 2-phosphaethynolate [Na[OCP]·(dioxane) x ], tetraphenyldipnictogen (Ph 2 Pn–PnPh 2 ) compounds are produced, and an insoluble precipitate forms from solution. In contrast, when the N -heterocyclic carbene adduct (NHC)–PnPh 2 Cl is combined with [Na[OCP]·(dioxane) x ], Sb– and Bi–phosphaketene complexes are isolated. Thus, NHC serves as an essential mediator for the reaction. Immediately after the formation of an intermediary pnictogen–phosphaketene NHC adduct [NHC–PnPh 2 (PCO)], the NHC ligand transfers from the Pn center to the phosphaketene carbon atom, forming NHC–C(O)P-PnPh 2 [Pn = Sb ( 3 ) or Bi ( 4 )]. In the solid state, 3 and 4 are dimeric with short intermolecular Pn–Pn interactions. When compounds 3 and 4 are heated in THF at 90 and 70 °C, respectively, the pnictogen center Pn III is thermally reduced to Pn II to form tetraphenyldipnictines (Ph 2 Pn–PnPh 2 ) and an unusual bis -carbene-supported OCP salt, [(NHC) 2 OCP][OCP] ( 5 ). The formation of compound 5 and Ph 2 Pn–PnPh 2 from 3 or 4 is unique in comparison to the known thermal reactivity for group 14 carbene–phosphaketene complexes, further highlighting the diverse reactivity of [OCP] − with main-group elements. All new compounds have been fully characterized by single-crystal X-ray diffraction, multinuclear NMR spectroscopy ( 1 H, 13 C, and 31 P), infrared spectroscopy, and elemental analysis ( 1 , 2 , and 5 ). The electronic structure of 5 and the mechanism of formation were investigated using density functional theory (DFT).

A Thermally Stable Magnesium Phosphaethynolate Grignard Complex

“…At the same temperature, a previously unresolved CP doublet in the 13 C­{ 1 H} NMR spectrum was observed at 166.8 ppm ( 1 J CP = 48.1 Hz), and the corresponding 31 P­{ 1 H} resonance (δ −378.3 ppm) is slightly shifted downfield. Notably, the observation of a 1 J ( 13 C– 31 P) coupling constant is without precedent for group 2 phosphaethynolate complexes due to rapid solution-state decomposition of previously reported complexes. , However, this coupling constant is smaller than reported values for “interaction-free” OCP anions (62.0–63.2 Hz) ,, and in the range of contacted OCP moieties in the s-block. , In the solid-state IR spectrum, two overlapping bands (vs) at 1800 and 1770 cm –1 were attributed to the OCP asymmetric stretch and are in the range of uncoordinated OCP anions. , Thus, 4 Me is best described as a charge-separated ion pair in the solid-state, although bound [Mg]–OCP forms may exist in solution.…”

“…In the direct synthesis of compound Notably, the observation of a 1 J( 13 C− 31 P) coupling constant is without precedent for group 2 phosphaethynolate complexes due to rapid solution-state decomposition of previously reported complexes. 9,10 However, this coupling constant is smaller than reported values for "interaction-free" OCP anions (62.0−63.2 Hz) 7,25,26 and in the range of contacted OCP moieties in the s-block. 4,5 In the solid-state IR spectrum, two overlapping bands (vs) at 1800 and 1770 cm −1 were attributed to the OCP asymmetric stretch and are in the range of uncoordinated OCP anions.…”

“…4,5 In the solid-state IR spectrum, two overlapping bands (vs) at 1800 and 1770 cm −1 were attributed to the OCP asymmetric stretch and are in the range of uncoordinated OCP anions. 26,27 Thus, 4 Me is best described as a charge-separated ion pair in the solid-state, although bound [Mg]−OCP forms may exist in solution.…”

Fluorescent organo-antimony compounds as precursors for syntheses of redox-active trimeric and dimeric alkali metal antimonides: an insight into electron transfer reduction processes

“…35 Recently, Gilliard and coworkers reported the NHC adduct of the antimony compound (NHC)-SbPh 2 Cl, where the C carbene signal appears at 146.5 ppm. 36 The same group also reported carbene-and carbone-stabilized bismuth mono-, di-, and tri-cations. 37 The NHC-and cAAC-supported bismuth cations were prepared via directly treating the more sterically crowded carbene ligands with [Ph 2 Bi(µ-Cl)] 2 .…”

Recent advances in the chemistry of the phosphaethynolate and arsaethynolate anions

“…In 2021, Gilliard and co-workers utilized [Na(dioxane) x ](OCP) to synthesise Sb- and Bi-phosphaketene complexes and their thermal reduction to dipnictines along with a unique [(NHC) 2 OCP][OCP] salt. 71 The reaction of the NHC–diphenylpnictogen halide complex ((NHC)–PnPh 2 Cl; Pn = Sb and Bi) with [Na(dioxane) x ](OCP) in THF yielded NHC–phosphaketene adducts ( 81 = Sb and 82 = Bi, Scheme 27). 31 P NMR showed resonance at δ = 58.2 ppm (Sb) and δ = 82.2 ppm (Bi), downfield from the main-group phosphaketene complexes ( δ = −441 to −225.8 ppm).…”