Synthesis, stereochemistry and crystal structures of cobalt(III) complexes containing 5,8-diphenyl-2,11-dithia-5,8-diphosphadodecane or 5,9-diphenyl-2,12-dithia-5,9-diphosphatridecane

Twelve new cobalt(III) complexes containing a tetradentate phosphine ligand of the type MeS(CH₂)₂PPh(CH₂)_nPPh(CH ₂)₂SMe (n = 2 L¹ or 3 L²) were prepared. Their structures were assigned on the basis of electronic absorption and ¹H NMR spectra and the molecular structures of cis-α-[CoCl₂{rac(P)-L¹}]BF₄ and trans-[CoCl₂{meso(P)-L²}]BF₄ were determined by single-crystal X-ray diffraction. The last two complexes comprise a slightly distorted octahedron with bond distances Co-P 2.210(1), Co-S 2.254(1) and Co-Cl 2.281(1) and Co-P 2.227(3), Co-S 2.327(3) and Co-Cl 2.241(3) Å (all averages) respectively. The differences in Co-S and Co-Cl bond distances are attributable to the strong trans influence of the phosphino group. Acetylacetonate complexes of rac(P)-SPPS in organic solvents form equilibrium mixtures of the cis-α and cis-β isomers, the molar ratio in MeNO₂ solution at 60°C being 2:1 for the L¹ complex and 3:2 for the L² complex.