Structural diversity of metallacycle intermediates for ethylene dimerization on heterogeneous NiMCM-41 catalyst: a quantum chemical perspective

Nanocluster models were investigated to explore the diversity of metallacycle intermediates for ethylene dimerization over NiMCM-41 at B3LYP/6-311+G* and M06/Def2-TZVP. The thermodynamic favorability of the formation of matallacycle with respect to the ring size of silica varied in the sequence of 6T<3T<2T<5T<4T in terms of Gibbs free energy (ranging from -10.01 to 16.66kcal/mol at B3LYP/6-311+G*). The reaction cycle faced lower barriers on 3T and 2T clusters, however. The formation of the intermediate and complexation of 1-butene led to positive total charges on the hydrocarbon segment of the complex, being maximized on four-membered sites and minimized on two-membered ones. Further insights are also provided with QTAIM, frontier orbital, and FTIR analyses.