Synthesis and Structure of Triphenylphosphonium Bis(diphenylstibino)methylide: A Conformational Study

The title compound was prepared in a high-yield one-pot synthesis from chlorodiphenylstibine and triphenylphosphonium methylide. Methyltriphenylphosphonium chloride is the only transylidation byproduct. The structure of the new ylide was determined by X-ray diffraction methods (monoclinic, space group P2₁/n, Z = 4, a = 1094.7 (2) pm, b = 1451.4 (2) pm, c = 2276.8 (4) pm, β = 90.67 (1)°). In the crystal, the molecule adopts the conformation B (R = C₆H₅) with the lone pairs of electrons at the antimony atoms oriented in the plane of the heavy atoms (P1, Sbl, Sb2) which also includes the ylidic carbon atom Cl. The conformation is analogous to that found recently for the phosphorus compound A (R = C₆H₅) both in the crystal and in solution. The pronounced conformational preference is discussed in terms of lone pair repulsion and of electrostatic and steric forces. Parallels in the structures of diphosphinoamines and-methanides are pointed out, along with their relevance for coordination chemistry.