Synthesis and Characterization of a New Chiral Phosphinothiol Ligand Derived from (−)-Menthone and Its Palladium(II) and Platinum(II) Complexes

Abstract

The chiral ligand (1R,2S,5R)-1-((diphenylphosphino)methyl)-2-isopropyl-5-methylcyclohexanethiol (4) has been prepared from low-cost commercial (−)-menthone in a three-step enantioselective synthesis. Oxidative addition of 2 equiv of this phosphinothiol ligand to [Pd0(PPh3)4] gave the enantiopure bis(phosphinothiolate)palladium(II) complex 5, which only exists as the trans-P,P geometrical isomer, in both the solid state and solution, owing to the preference of the chelate rings to adopt the λ conformation in which the position of the menthane ring does not allow a conformation of the phenyl groups compatible with the more sterically hindered cis geometry. These stereoelectronic coordination preferences of the chiral phosphinothiolate ligand have been confirmed by the structure of the analogous Pt(II) complex 6, which also exhibits the trans-P,P geometry exclusively, both in the solid state and in solution. Crystals of 5·1/2CH2Cl2 and 6·1/2CH2Cl2 are isomorphic, belonging to the monoclinic crystal system C2...