Effect of phosphorus-donor ligands on the isomerisation of pentenes catalysed by substituted derivatives of H 4Ru 4(CO) 12

Abstract

The catalytic activity of H 4Ru 4(CO) 11L (where is PPh 3, P(OEt) 3, P(OPh) 3), H 4Ru 4(CO) 10 [P(OEt) 3] 2 and H 4Ru 4(CO) 8[P(OEt) 3] 4 in the isomerisation of pentenes in toluene at 70.4 °C is described. The initial conversion rate is proportional to the catalyst concentration, decreases with increasing CO pressure, while the addition of the free ligand causes a decrease of the conversion rate, in the initial steps, ascribed to its preferential coordination on the active sites. For H 4Ru 4(CO) 11L, the isomerisation rate decreases with L in the sequence P(OEt) 3 > (P(OPh) 3 > PPh 3 > CO. The conversion rate, moreover, decreases with n in the series H 4Ru 4(CO) 12−n[P(OEt) 3] n (n = 1, 2, 4). The results are interpreted by suggesting that the RuCO bonds are mainly involved in the active site formation and that the phosphorus-donor ligands cause a weak increase of the activity of the carbonyl groups. However, the free sites formed by RuCO bond cleavage of Ru(CO) 2L units are considered to give a little contribution to the isomerisation for the steric hindrance of L.