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

The new dithiol ligand (+)-H2BCOS ((+)-1) has been synthesized. The tetranuclear rhodium complex [Rh-2(mu-BCOS)(cod)(2)](2) (8) (cod = cycloocta-1,5-diene) was prepared by starting with the dinuclear complex [Rh(mu-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 [Rh-2(mu-BCOS)(CO)(2)(PPh3)(2)] (10) was prepared and studied by IR and P-31 NMR. The [Rh-2(mu-(+)-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. (C) 1997 Elsevier Science S.A.