Homogeneous catalysis of olefin isomerisation. Part II. (a) Isomerisation of pent-1-ene catalysed by hydridochlorotris(triphenylphosphine)-ruthenium(II) in benzene; and (b) a novel procedure for evaluating velocity constants for a network of three first-order reversible reactions

Abstract

The isomerisation of pent-1-ene to cis-pent-2-ene (60%) and trans-pent-2-ene (40%) is catalysed at 50° by solutions of RuHCl(PPh₃)₃ in benzene. Reaction is of the first order with respect both to complex and to pent-1-ene when the concentrations of each are low. Departures from first-order behaviour occur because the catalytically active species are formed by dissociation of the complex, and because of changes in the nature of the solvent at the higher pentene concentrations. Interference of the reaction by-products is slight. The six velocity constants for the interconversion of the three pentene isomers have been determined by a new procedure involving the use of Laplace–Carson transforms.

Isomerisation of deuterium-labelled pent-1-ene has revealed (i) that equilibrium is established between uncoordinated and co-ordinated pent-1-ene, (ii) that redistribution of deuterium in pent-1-ene accompanies its isomerisation, (iii) that normally isomerisation involves the movement of the double bond to the adjacent position only, (iv) that cis-and trans-pent-2-ene are each formed by a mechanism involving a pentyl intermediate, (v) that a mechanism involving a π-allylic intermediate also contributes to the formation of the trans-isomer, and (vi) that some processes require the formation of transient species having two hydrogen atoms as ligands of ruthenium and in which two phosphine ligands have been lost by dissociation.