Kinetic and Thermodynamic Preferences in Aryl vs Benzylic C−H Bond Activation with Cationic Pt(II) Complexes

Anhydrous cationic Pt(II) complexes [(NN)Pt(CH3)(CF3CD2OD)]+ (1, NN = ArNC(Me)−C(Me)NAr), which are obtained by reaction of (NN)Pt(CH3)2 with B(C6F5)3 in CF3CD2OD, activate C−H bonds of benzene and methylbenzenes, with enhanced reactivity compared to the previously prepared equilibrium mixtures with the (thermodynamically favored) aquo complexes. For methylbenzenes (toluene, p-xylene, mesitylene), activation at the aromatic and benzylic positions are kinetically competitive, but the product of the latter is strongly favored thermodynamically. This unusual trend is attributed to formation of η3-benzyl structures, which can be observed spectroscopically for 1,4-diethylbenzene activation.

无水阳离子型铂(II)配合物[(NN)Pt(CH₃)(CF₃CD₂OD)]⁺（1，其中NN为ArN=C(Me)−C(Me)=NAr）由(NN)Pt(CH₃)₂与三(五氟苯基)硼(B(C₆F₅)₃)在CF₃CD₂OD中反应制得。该配合物可活化苯与甲基苯的C-H键，相较于此前制备的以热力学稳定的水合配合物为主要组分的平衡混合物，其反应活性显著提升。对于甲基苯（甲苯、对二甲苯、均三甲苯）而言，芳环位点与苄基位点的C-H活化在动力学上具有竞争性，但热力学上更倾向于生成苄基活化产物。这一反常趋势可归因于η³-苄基结构的形成，在1,4-二乙基苯的活化反应中可通过光谱学手段观测到该类结构。