K2CO3-Promoted Consecutive Carbon–Hydrogen and Carbon–Carbon Bond Activation of Cycloheptane with Rhodium(III) Porphyrin Complexes: Formation of Rhodium Porphyrin Cycloheptyl and Benzyl

Abstract

K2CO3-promoted carbon–hydrogen and carbon–carbon bond activations of cycloheptane are achieved with rhodium(III) tetrakis(4-tolyl)porphyrin chloride (Rh(ttp)Cl) at 120 °C to give Rh(ttp) cycloheptyl and benzyl complexes. On the basis of mechanistic studies, Rh(ttp)Cl first reacts by ligand substitution to give Rh(ttp)OH, which then undergoes reductive elimination to give RhII2(ttp)2. The metalloradical RhII(ttp), formed via dissociation of RhII2(ttp)2, activates the CH bond of cycloheptane to form Rh(ttp)(cycloheptyl) and Rh(ttp)H. Rh(ttp)(cycloheptyl) slowly yields Rh(ttp)(cycloheptatrieneyl) by successive β-hydride elimination to olefins and Rh(ttp)H. K2CO3 promoted the dehydrogenation of Rh(ttp)H to give RhII2(ttp)2 and H2. Both Rh(ttp)H and RhII2(ttp)2 activate the cycloheptatriene to give Rh(ttp)(cycloheptatrienyl), which further undergoes a RhII(ttp)-catalyzed skeletal rearrangement to form Rh(ttp)Bn with rate enhancement much faster than that of the analogous organic isomerization of cycloheptatriene to toluene.