Hydroformylation of formaldehyde with the [Rh(CO)2Cl2]- and [Rh5(CO)15-x(PPh3)x]- system: A case of synergetic catalysis with two combined rhodium carbonyl species in different oxidation states

Article abstract of DOI:10.1021/om00146a028

Paraformaldehyde has been hydroformylated to glycolaldehyde at 100-140 atm of CO and H₂ (1/1) and at 90-110°C with selectivity up to 95% in common organic solvents, e.g., acetone, with a catalytic system involving two preformed anionic rhodium carbonyl species in different formal oxidation states, viz., [Rh(CO)₂Cl₂]^- and [Rh₅(CO)_15-x(PPh₃)_x]^-. This system combines the high activity of the latter with the high selectivity of the former and enables the hydroformylation of paraformaldehyde to be carried out at a rate comparable with that previously observed only in N,N-disubstituted amide or pyridine solvents. A strictly related system, generated in situ upon addition of halide ions and triphenylphosphine to Rh₄(CO)₁₂, showed comparable catalytic behavior. A temptative interpretation of the synergetic effect shown by mixtures of [Rh(CO)₂Cl₂]^- and [Rh₅(CO)_15-x(PPh₃)_x]^- is suggested.