Reaction mechanisms of metal–metal-bonded carbonyls. Part 14. Reactions of 1,1,1,2,2,2,3,3,3-nonacarbonyl-1,2,3-tris(triphenylphos-phine)-triangulo-triruthenium

Abstract

Some reactions of the complex [{Ru(CO)₃(PPh₃)}₃], in decalin between 40 and 150 °C, have been studied and found to proceed by three kinetically distinct paths leading to a variety of products. Reactions with tributylphosphine, carbon mono-oxide, and low concentrations of triphenylphosphine under an atmosphere of argon occur by path A which involves reversible loss of PPh₃ at some stage. The limiting rate at [PPh₃]= 0 is governed by the parameters k_lim.^A(100 °C)= 2 × 10^–1 s^–1, ΔH^‡= 122.8 ± 2.1 kJ mol^–1. and ΔS^‡= 68.6 ± 6.2 J K^–1 mol^–1. Reaction with PPh₃, under an atmosphere of argon and at values of [PPh₃] sufficient to completely suppress path A, occurs by path B which involves reversible loss of CO at some stage. The limiting rate at [CO]= 0 is governed by the parameters k_lim.^B(100 °C)= 1.0 × 10^–5 s^–1, ΔH^‡= 137.8 ± 4.4 kJ mol^–1, and ΔS^‡= 27.2 ± 10.9 J K^–1 mol^–1. Reaction with PPh₃ in the presence of sufficient PPh₃ and CO to completely inhibit reaction by paths A and B proceeds by C for which k_lim.^c(at 100° C)= 5.7 × 10^–7 s^–1, ΔH^‡= 147.9 ±3.9 kJ mol^–1. and ΔS^‡= 29.6 ± 9.2 J K^–1 mol^–1. The three paths may simply involve the three distinct primary processes: reversible PPh₃ dissociation (A), reversible CO dissociation (B), and fission into mono- and hi-nuclear fragments (C). It is possible, however, that these three processes are preceded by a common initial step involving reversible fission of a single Ru–Ru bond.