Heats of the reactions of tricarbonyl(naphthalene)chromium, tricarbonyl(cycloheptatriene)chromium, tricarbonyl(cycloheptatriene)tungsten, and tricarbonyltris(ethylcyanide)tungsten with pyridine, phosphines, phosphites, and other ligands : comparative thermochemical study of L3M(CO)3 complexes (M = Cr, Mo, W)

Abstract

Enthalpies of ligand substitution based on reaction of (cycloheptatriene)Cr(CO)3, (naphthalene)Cr(CO)3, (cycloheptatriene)W(CO)3, (EtCN)3W(CO)3, and (arene)W(CO)3 complexes with a series of ligands have been measured by solution calorimetry. These data generate an order of thermochemical stability for the complexes L(n)M(CO)3 (M = Cr, W). These data are combined with earlier data reported for analogous organomolybdenum complexes and allow comparison of relative enthalpies of ligand substitution as a function of the metal. Referenced to the (eta6-C6H6)M(CO)3 complex, ligand substitution reactions producing L(n)M(CO)3 become increasingly exothermic in going from Cr to Mo to W, in keeping with the expected increase in bond strength in going from a first- to a second- to a third-row metal