Density Functional Study on the Carbostannylation of Aryne by the Palladium(0)−Iminophosphine Catalyst. Does the Apical Site Really Contribute to the Catalytic Reaction?

Abstract

The mechanism of carbostannylation of aryne by the palladium(0)−iminophosphine catalyst was examined using the density functional method (B3LYP) paying attention to the role of the apical site. The calculations showed that the catalytic reaction takes not cycle A but cycle B out of two possible cycles (cycle A: 1 → 3 → 1; cycle B: 1 → 4 → 1). It was found that the apical site is an origin of the catalysis of the palladium(0)−iminophosphine complex. The contribution of the apical site lowers the energy barrier of the rate-determining step and makes the catalytic reaction possible. The Sn−C σ-bond breaking of SnH3C⋮CH, which is a rate-determining step in cycle B, proceeds by the heterolytic mechanism without the oxidative addition of the Sn−C σ-bond to Pd (path b). However, when the Pd atom is replaced by the Pt atom, the homolytic cleavage of the Sn−C σ-bond with the oxidative addition to Pt (path c) becomes energetically more favorable.