HYDROCARBONYLATION OF PROP-2EN-1-OL TO BUTANE-1,4-DIOL AND 2-METHYLPROPAN-1-OL CATALYZED BY RHODIUM TRIETHYLPHOSPHINE COMPLEXES

The hydrocarbonylation of prop-2-ene-1-ol catalysed by [Rh-2(O(2)CMe)( 4)]-PEt(3), which gives [RhH(CO)(PEt(3))(2)] as the active species, ha s been found to produce predominantly butane-1,4-diol and 2-methylprop an-1-ol with small amounts of 2-methylpropane-1,3-diol and propan-1-ol . Neither 2-methylprop-2-enal nor 2-methylprop-2-en-1-ol are intermedi ates in the production of 2-methylpropan-1-ol. By carrying out the rea ction under a variety of reaction conditions and by using deuterium-la belling studies it was possible to formulate a mechanism for the produ ction of 2-methylpropan-1-ol which involves formation of the vinyl alc ohol, 2-methylprop-1-en-1-ol, as the primary product followed by tauto merism and hydrogenation, provided that at least two PEt(3) groups are co;ordinated to the rhodium. A dehydration is proposed to occur durin g the catalytic cycle from a cationic hydroxycarbene intermediate. Usi ng propenyl ethers as substrates similar products are obtained presuma bly via loss of alcohol rather than dehydration. If less than two PEt( 3) groups ale co-ordinated to rhodium the major branched-chain product from prop-2-en-1-ol is 2-methylpropane-1,3-diol. This is interpreted as indicating that protonation of the acyl intermediate and dehydratio n of the hydroxycarbene do not occur because of the lower electron den sity on the acyl O atom.