Density Functional Study on the Mechanism of the Oxidative Addition of the Highly Polarized Sn−C σ-Bond to the (LH₃)(L‘H₃)Pd and (LH₂C₂H₄LH₂)Pd (L, L‘ = N, P, As, Sb) Complexes

The electronic effect on the activation mechanism of the highly polarized Sn−C σ-bond is theoretically examined by means of a density functional method (B3LYP) using palladium model complexes with various ligands, (LH 3 )(L‘H 3 )Pd and (LH 2 C 2 H 4 LH 2 )Pd (L, L‘ = N, P, As, Sb). The author has recently reported a novel activation mechanism of the highly polarized Sn−C σ-bond of SnH 3 C⋮CH in a previous paper (Matsubara et al. Organometallics 2002, 21, 4482−4489). The Sn−C σ-bond approaches the Pd perpendicularly to the P−Pd−P plane of (PH 3 ) 2 Pd, and the activation of the Sn−C σ-bond takes place by two steps via the unique intermediate 2P, because the apical site of the palladium complex plays an important role in the activation. When the phosphine ligand is replaced by the more σ-donative nitrogen ligand or the chelate ligand, the mechanism is drastically changed, and the activation of the Sn−C σ-bond occurs in the L−Pd−L‘ plane throughout by one step from the π-complex. In contrast, in the case of the substrate SnH 3 (H)C CH 2, the activation of the Sn−C σ-bond starts from the π-complex independent of the ligands. However, the reaction proceeds by the perpendicular approach of the Sn−C σ-bond with the support of the apical site, which is accompanied by the clockwise or the counterclockwise rotation of the coordinated substrate. It was found that the counterclockwise rotation, where the apical site effectively contributes to the reaction, was energetically more favorable.