Theoretical Study of the Oxidative Addition of Ammonia to Various Unsaturated Low-Valent Transition Metal Species

Abstract

Reaction profiles for the oxidative addition of NH3 to a number of unsaturated low-valent transition metal complexes have been computed using gradient-corrected density functional theory. The metal complexes studied are d8 CpM(CO) (M = Rh, Ir) and trans-M(PH3)2X (M = Rh, Ir; X = H, Cl) and d10 ML2 (M = Pd, Pt; L = PH3, L2 = H2PCH2CH2PH2, dpe). Reactions with the d8 species are characterized by the formation of strongly bound ammine complexes from which computed activation energies for oxidative addition are in excess of 16 kcal mol-1. Computed reaction enthalpies are all exothermic with these complexes. With d10 M(PH3)2 species computed ammine adducts are weak, activation barriers are in excess of 23 kcal mol-1, and the overall reaction is endothermic for both M = Pd and Pt. The introduction of the chelating dpe ligand results in stronger ammine adducts but only slightly reduced computed activation barriers. Of the d10 species only the reaction with Pt(dpe) is computed to be exothermic. Comparison of the ...