A Mechanistic Investigation of the Carbon−Carbon Bond Cleavage of Aryl and Alkyl Cyanides Using a Cationic Rh(III) Silyl Complex

Cationic Rh(III) complex [Cp*(PMe3)Rh(SiPh3)(CH2Cl2)]BAr4‘ (1) activates the carbon−carbon
bond of aryl and alkyl cyanides (R−CN, where R = Ph, (4-(CF3)C6H4), (4-(OMe)C6H4), Me, iPr, tBu) to
produce complexes of the general formula [Cp*(PMe3)Rh(R)(CNSiPh3)]BAr4‘. With the exception of the
tBuCN case, every reaction proceeds at room temperature (t1/2 < 1 h for aryl cyanides, t1/2 < 14 h for alkyl
cyanides). A general mechanism is presented on the basis of (1) an X-ray crystal structure determination
of an intermediate isolated from the reaction involving 4-methoxybenzonitrile and (2) kinetic studies performed
on the C−C bond cleavage of para-substituted aryl cyanides. Initial formation of an η1-nitrile species is
observed, followed by conversion to an η2-iminoacyl intermediate, which was observed to undergo migration
of R (aryl or alkyl) to rhodium to form the product [Cp*(PMe3)Rh(R)(CNSiPh3)]BAr4‘.

阳离子铑(III)配合物[Cp*(PMe3)Rh(SiPh3)(CH2Cl2)]BAr4‘（化合物1）可活化芳基与烷基氰化物（R−CN，其中R = Ph、(4-(CF3)C6H4)、(4-(OMe)C6H4)、Me、iPr、tBu）的碳-碳键，生成通式为[Cp*(PMe3)Rh(R)(CNSiPh3)]BAr4‘的配合物。除叔丁基氰（tBuCN）外，所有反应均可在室温下进行（芳基氰化物的半衰期t1/2 < 1 h，烷基氰化物的半衰期t1/2 < 14 h）。基于两项研究工作提出了通用反应机制：(1) 对由4-甲氧基苯甲腈参与的反应中分离得到的中间体进行X射线晶体结构测定；(2) 对对位取代芳基氰化物的碳-碳键裂解过程开展动力学研究。观测到反应首先生成η¹-腈类物种，随后转化为η²-亚氨酰中间体；该中间体可发生R（芳基或烷基）向铑的迁移，最终生成目标产物[Cp*(PMe3)Rh(R)(CNSiPh3)]BAr4‘。