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.