Kinetics and mechanism of ligand substitution reactions in [cis-M(CO)4(amine)(EPh3)] complexes (M = Mo, W; amine = pyridine, piperidine; E = As, Sb)

Abstract

Group 6 metal carbonyls [cis-M(CO)4(amine)(EPh3)] (M = Mo, W; amine = piperidine (pip), pyridine (py); E = As, Sb) have been prepared and characterized. These complexes react thermally in chlorobenzene solutions with phosphine or phosphite ligands (= L) to give cis- and trans-M(CO)4(L)(EPh3) products. Kinetics of amine substitution by L in these complexes, under pseudo-first-order conditions, indicate that these reactions proceed by a rate law that is first-order in concentration of the metal complex. Rate constants and activation parameters for these reactions have been determined and are discussed. Competition studies for the [M(CO)4(EPh3)] intermediates show that these intermediates are highly reactive and react almost indiscriminately with various incoming nucleophiles with slight preference for more basic ones.