Modelling proposed intermediates in the hydrocarbonylation of alkenes catalysed by rhodium complexes of PBu3i and PPr3i

In ethanol, hydrocarbonylation reactions of alkenes catalysed by triethylphosphine complexes of rhodium give alcohols as the products with low linear selectivity, whilst rhodium complexes of PPr3i or PBu3i give mainly aldehydes, again with low linear selectivity. Modelling the proposed acyl intermediates by studying [Rh(C(O)Me)(CO)(m)(L)(4-m)] (L = PPr3i or PBu3i) shows that they exist as monophosphine species under the normal reaction conditions. In the absence of CO, [Rh(=C(OH)Me)(CO)L-2](+) can also be formed. The implications of these NMR studies for the chemo-and regio-selectivity of the hydrocarbonylation reactions are discussed.