Synthesis and Structure of Gold and Platinum Menthyl Complexes

A Grignard reagent derived from (−)-menthyl chloride has been reported to be a 1:1 mixture of menthyl magnesium chloride and neomenthyl magnesium chloride, which do not interconvert. Addition of an excess of this reagent to Au(PPh₃)(Cl) or Pt(dppe)Cl₂ gave Au(PPh₃)(Men) (1) and Pt(dppe)(Men)(Br) (2), respectively. Crystallographic studies of these first well-characterized transition metal menthyl complexes showed that the menthyl group adopts a conformation with all three substituents in equatorial positions. NMR spectroscopic data for 2 showed that menthyl has a large trans influence, comparable to other alkyl groups. Decomposition of 1 in CDCl₃ gave Au(PPh₃)(Cl) and a mixture of menthyl chloride and neomenthyl chloride, while 2 formed the halide complexes Pt(dppe)Cl₂, Pt(dppe)Br₂, and Pt(dppe)(Br)(Cl) and a mixture of 2-menthene and 3-menthene.