An ab initio investigation of σ-bond metathesis and insertion reactions of acetylene with Cl 2ZrH + and Cl 2ZrCH 3+

Abstract

All-electron RHF and RMP2 ab initio calculations with split-valence basis sets of double- and triple-ξ quality have been used to study reaction paths for the reaction of acetylene ( 1) with the model compounds Cl 2ZrH + ( 2) and Cl 2ZrCH 3 + ( 3). At the RMP2/ /RHF level the acetylide-complex formation reaction is calculated to have a barrier of 15.8 ( 2), 20.8 ( 3) kcal/mol with respect to complexed acetylene and to be 44.4 ( 2), 18.9 ( 3) kcal/mol exothermic with respect to free acetylene. The transition states are four-membered cycles. The calculated energy barriers are greater than the theoretical values obtained for σ-bond metathesis of acetylene with Cl 2ScR and Cp 2ScR (R = H, CH 3). The calculated energetics of the metathesis reaction path are compared with the theoretical values determined for the alternative insertion reaction of acetylene into ZrH and ZrC σ bonds. The insertion reactions are kinetically and thermodynamically favoured over the corresponding metathesis reactions.