A potential route to the formation of alkylidene ligand from two mutually cis alkene ligands: a DFT study

Abstract

Listen

Translate article

The possible reaction pathways have been studied for the transformation of cis-[W(CO) 4(η 2-C 2H 4) 2] into alkylidene complex by density functional theory (B3LYP) calculations in order to explain how the catalytically active alkylidene species can be formed from the bis-olefin complexes of tungsten. It was found that the two-electron oxidation of cis-[W(CO) 4(η 2-C 2H 4) 2] ( 2et) to its dicationic form cis-[W(CO) 4(η 2-C 2H 4) 2] 2+ ( 2et 2+ ) allowed for the transformation of this complex to tungstacyclopentane [W(CO) 4(C 4H 8)] 2+ ( cp 2+ ) at lower energy (Δ H=24 and Δ G=36 kJ mol −1) than in the case of the neutral compound 2et (Δ H=105 and Δ G=108 kJ mol −1). The electronic structure and energy of the initial 2et 2+ , as well as the mechanism of its interconversion to the tungstacyclopentane complex cp 2+ and the final butylidene complex [W(CO) 4(=CHC 3H 7)] 2+ ( but 2+ ) were determined. An activation barrier Δ H # for the formation of the cp 2+ and but 2+ complexes was found to be 48 and 87 kJ mol −1, respectively. The butylidene complex but 2+ is lower in energy than the tungstacyclopentane complex cp 2+ and remains more stable than the initial cis-bis(ethene) complex 2et 2+ . The structures of two potential hydrido complexes [W(CO) 4H(C 4H 7)] 2+ ( Hcp 2+ ) are also discussed. The theoretical results are compared with available experimental data, as well as the results of theoretical studies that have been carried out on the related systems.