BEHAVIOR OF WATER-SOLUBLE DINUCLEAR RHODIUM COMPLEXES IN THE HYDROFORMYLATION REACTION OF OCT-1-ENE

The biphasic hydroformylation reaction of oct-1-ene, has been investigated by using the water-soluble dinuclear complex [Rh2(mu-S(t)Bu)2(CO)2(TPPTS)2] as precursor. Addition of ethanol as a cosolvent dramatically improved the yields but the good regioselectivity in linear aldehyde observed for neat oct-1-ene-water systems (97%) decreased to 83% (for 22% ethanol w/w). It is shown that the dinuclear framework cannot be maintained, that the mononuclear complex [RhH(CO)(TPPTS)3] is formed, and that thiol and significant amounts of [Rh2(mu-S(t)Bu)2(CO)4] move into the organic phase. This reaction from the dinuclear species requires the simultaneous presence of water and carbon monoxide. Introduction of the water-soluble thiol HS(CH2)3NMe2 in the bridging positions affords the complex [Rh2(mu-S(CH2)3)NHMe2)2(CO)2(TPPTS)2]Cl2 which can be kept in the aqueous phase but has a low level of catalytic activity.