Synthesis of rhodium(I) complexes with the new dithiol chiral ligand (+)-trans-2,3-bis(mercaptomethyl)-bicyclo[2.2.2]octane (H2BCOS) their application as catalysts precursors in the styrene hydroformylation

Abstract

The new dithiol ligand (+)-H2BCOS ((+)-1) has been synthesized. The tetranuclear rhodium complex [Rh2(μ-BCOS)(cod)2]2 (8) (cod = cycloocta-1,5-diene) was prepared by starting with the dinuclear complex [Rh(μ-OMe)(cod)]2 (7) through an exchange reaction with the dithiol ligand. The reactivity of 8 towards CO and phosphorus-donor ligands was studied; the mixed CO/P complex [Rh2(μ-BCOS)(CO)2(PPh3)2] (10) was prepared and studied by IR and 31P NMR. The [Rh2(μ-(+)-BCOS)(cod)2]2 complex was tested as a catalyst precursor in the enantioselective hydroformylation of styrene. The influence of P-donor as modifying ligand, temperature and pressure on the catalytic activity and selectivity was explored, achieving ee up to 55% with total conversion into aldehydes in the presence of BDPP. These results revealed a slight cooperative effect between the dithiolate and the diphosphine ligands.