Statistical Modeling of Gas-Phase Organometallic Reactions Based on Density Functional Theory: Ni+ + C3H8

Abstract

Density functional theory in its B3LYP variant has been used to explore quantitative details of the adiabatic potential energy surface leading from Ni+ + C3H8 reactants through a deep Ni+(C3H8) well to NiC2H4+ + CH4 and NiC3H6+ + H2 elimination products. The lowest energy path to CH4 elimination involves facile CC bond insertion followed by a high multicenter transition state (MCTS) leading directly to the exit-channel complex Ni+(C2H4)(CH4). The lowest energy path to H2 elimination involves comparably facile secondary CH insertion followed by a comparably high MCTS leading directly to the Ni+(C3H6)(H2) complex. Primary CH insertion leads to significantly higher barriers to both CH4 and H2 elimination; in particular, β-methyl migration is energetically very costly. These results support a mechanism significantly different from the stepwise mechanisms invoked earlier but the same as that found in recent calculations on the Fe+ + C3H8 reaction by Holthausen and Koch. The geometries suggest that agostic inte...