The kinetics of the reaction of RuCl(H)(PPh₃)₃ with dienes and trienes

RuCl(H)(PPh₃)₃ is a valuable catalyst. It is a very efficient hydrogenation catalyst but has proven difficult to study kinetically. The consumption of hydrogen during the catalytic cycle is very rapid and the kinetics are limited by the rate of hydrogen dissolving into the solvent. We had found that RuCl(H)(PPh₃)₃ reacts with dienes and trienes to give allyls and dienyls.

These reactions were exploited to determine the mechanism of the key step of the insertion of an alkene into the Ru-H bond of RuCl(H)(PPh₃)₃. It was shown that the mechanism has two pathways, a direct attack of the diene or triene on RuCl(H)(PPh₃)₃ and the preferred pathway of PPh₃ loss to give RuCl(H)(PPh₃)₂ which is followed by attack of diene or triene.

It is probable that when RuCl(H)(PPh₃)₃ is used as a hydrogenation catalyst, RuCl(H)(PPh₃)₂ is the species on the catalytic cycle.

References

M. Grassi, B. E. Mann, P. Manning, and C.M. Spencer, "The insertion of cycloheptatriene and cyclohepta-1,3-diene into the Ru-H bond of RuHCl(PPh₃)₃ to give Ru(h⁵-C₇H₉)Cl(PPh₃)₂ and Ru(h³-C₇H₁₁)Cl(PPh₃)₂", J. Organomet. Chem., 1986, 307, C55-C57.

B. E. Mann, P. W. Manning, and C. M. Spencer, "The preparation of (h-C₅H₅)RuCl(PPh₃)₂ from RuHCl(PPh₃)₃ and Penta-1,4-diene; Carbon-carbon bond formation by dehydrogenation", J. Organomet. Chem., 1986, 312, C64-C66.

G. Alibrandi and B. E. Mann, "The reaction of cyclo-octatetraene with [RuClH(PPh₃)₃]", J. Chem. Soc., Dalton Trans., 1992, pp. 1439-1442.

G. Alibrandi and B. E. Mann, "The kinetics of the reaction of [RuClH(PPh₃)₃] with various olefins", J. Chem. Soc., Dalton Trans., 1994, pp. 951-954.