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) (<b>1</b>) and Pt(dppe)(Men)(Br) (<b>2</b>), 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 <b>2</b> showed that menthyl has a large <i>trans</i> influence, comparable to other alkyl groups. Decomposition of <b>1</b> in CDCl₃ gave Au(PPh₃)(Cl) and a mixture of menthyl chloride and neomenthyl chloride, while <b>2</b> formed the halide complexes Pt(dppe)Cl₂, Pt(dppe)Br₂, and Pt(dppe)(Br)(Cl) and a mixture of 2-menthene and 3-menthene.