Formation of B−P Bonds through the Reaction of nido-Monophosphinocarboranes with Palladium(II) Complexes. The First Example of a Chelating R₂P−C−B−PR₂ Diphosphine

Reaction of [NMe₄][7-PPh₂-8-R-7,8-C₂B₉H₁₀] (R = Me, H, Ph) with cis-[PdCl₂(PPh₃)₂] in ethanol yielded [PdCl(7-PPh₂-8-R-11-PPh₂-7,8-C₂B₉H₉)(PPh₃)] (R = Me, H, Ph). The Pd(II) is in a square-planar arrangement. The carborane ligand chelates the Pd through two phosphorus atoms, one from C−PPh₂ and the second from the generated B(11)−PPh₂. The remaining two positions are filled by a PPh₃ and one chloride. In the complexation process, a previously nonexistent B(11)−P bond is generated in the ligand. This is unambiguously demonstrated by a doublet in the ¹¹B{¹H} NMR spectrum and a 1:1:1:1 quartet in the ³¹P{¹H} spectrum. The structure was fully elucidated by a crystal diffraction analysis of [PdCl(7-PPh₂-8-Me-11-PPh₂-7,8-C₂B₉H₉)(PPh₃)]·C₇H₈. By this reaction the hitherto unknown R₂P−C−B−PPh₂ chelating unit has been formed.