Hydroformylation and hydrocarbonylation of dicyclopentadiene with cobalt—rhodium catalytic systems promoted by triphenylphosphine: Synthesis of monoformyltricyclodecenes, diformyltricyclodecanes and di(tricyclodecenyl)ketones

A carbonyl cobalt—rhodium mixed system, promoted by the triphenylphosphine ligand, catalyzes in mild conditions the selective hydroformylation of endo-dicyclopentadiene. In the pressure range of 20–40 atm of syngas and at a temperature of 70–110 °C, an isomeric mixture of diformyltricyclodecanes is obtained in high yields and with selectivity up to 95%, as a result of two distinct and subsequent hydroformylation steps. The difference in the hydroformylation rates of the norbornenyl and cyclopentenyl moieties is so marked that dicyclopentadiene is almost completely converted to monoformyltricyclodecenes prior to the subsequent hydroformylation of the cyclopentenyl ring to any significant extent. The second hydroformylation step is also completely inhibited by adopting milder conditions (1 atm, 70–90 °C); at atmospheric pressure an isomeric mixture of 8-formyltricyclodec-*-enes (* =3,4) or di(tricyclodecenyl)ketones can be selectively obtained, mainly depending on the L/M ratio adopted. The monoformyltricyclodecenes, diformyltricyclodecanes and the di(tricyclodecenyl)ketones have been isolated in a pure state either by vacuum distillation or by liquid chromatography, and have been spectroscopically characterized by IR, 1H and 13C NMR, and mass spectroscopy. Bimetallic CoRh species, such as CoRh(CO)6(PPh3), probably play a key role in generating an active catalytic system in the experiments under pressure, as suggested by a synergetic effect between the two metals and almost quantitative recovery of either CoRh(CO)6(PPh3) or CoRh(CO)5(PPh3)2, depending on the adopted L/M ratio. In contrast, the system at ambient pressure is not only complicated by clusterization equilibria of the above species, but also by degradation reactions of PPh3 and carbonyl-substitution reactions with dicyclopentadiene which ultimately afford MCp(CO)2(M = Co, Rh; Cp = η5-C5H5) species. Irreversible formation of these latter species is probably at the origin of the deactivation process of the catalytic system. A possible mechanism which accounts for the change in selectivity from aldehydes to ketones depending on the L/M+Mt́ molar ratio, as well as the synergetic effect of cobalt and rhodium in the formation of the latter, is also suggested.