遷移金属錯本によるσ結合活性化とその関連反応に関する理論的研究

抄録

Though C-H σ-bond activation of methane by platinum (0) and palladium (0) complexes, M- (PH₃) ₂ (M=Pd or Pt), is significantly endothermic and requires a considerably large activation barrier, a platinum (0) chelate-phosphine complex can perform the C-H σ-bond activation. This is interpreted in terms of distortion energy and d orbital energy. However, a palladium (0) complex cannot perform it even with a chelate-phosphine. An electron-withdrawing CN group on the sp³ C atom also accelerates the C-H σ-bond activation, because the CN group stabilizes the transition state through a charge-transfer interaction between Pd d and CN π^* orbitals and strengthens the palladium-alkyl bond. As a result, the palladium (0) chelate-phsophine complex can perform the C-H σ-bond activation of dicyanomethane. On the other hand, a palladium (II) carboxylate complex easily perfomrs the C-H σ-bond activation of methane and benzene through heterolytic C-H bond fission. This bond fission is assisted by conversion of the carboxylate ligand to carboxylic acid.