Highly stereospecific carbene insertions into platinum–halide bonds. Crystal structure of [PtCl(S-CHClSiMe3)(S,S-Ph2PCHMeCH2CHMePPh2)]

Abstract

Trimethylsilyldiazomethane reacted with [PtX₂L₂][X = Cl, Br or I; L₂= cycloocta-1,5-diene (cod) or Ph₂P(CH₂)_nPPh₂ where n= 1–4] to give the corresponding [PtX(CHXSiMe₃)L₂] as a racemic mixture in high yields. The cod ligands in [PtX(CHXSiMe₃)(cod)] were readily displaced by diphosphines. When optically active complexes [PtX₂L₂][X = Cl, Br or I; L₂=(2S,3S)-2,3-bis(diphenylphosphino)butane, (2S,4S)-2,4-bis(diphenylphosphino)pentane (S,S-skewphos) or (4R,5R)-4,5-bis(diphenylphosphinomethyl )-2,2-dimethyl-1,3-dioxolane] were treated with trimethylsilyldiazomethane the products [PtX(CHXSiMe₃)L₂] were mixtures of diastereoisomers in different proportions ranging from 1 : 1 to 15 : 1. The major diastereoisomer of [PtCl(CHClSiMe₃)(S,S-skewphos)] was readily separated by fractional crystallisation and its crystal structure revealed that the configuration at the α-carbon was S. This compound is configurationally stable for at least 14 d in CDCl₃ solution as shown by ³¹P NMR spectroscopy. The high diastereoselectivities obtained in some of the reactions may originate from steric effects.