Reversible Homolysis of a Carbon–Carbon σ-Bond Enabled by Complexation-Induced Bond-Weakening
Suhong Kim, Pan‐Pan Chen, K. N. Houk, Robert R. Knowles
Abstract
A case study of catalytic carbon–carbon σ-bond homolysis is presented. The coordination of a redox-active Lewis acid catalyst reduces the bond-dissociation free energies of adjacent carbon–carbon σ-bonds, and this complexation-induced bond-weakening is used to effect reversible carbon–carbon bond homolysis. Stereochemical isomerization of 1,2-disubstituted cyclopropanes was investigated as a model reaction with a ruthenium (III/II) redox couple adopted for bond weakening. Results from our mechanistic investigation into the stereospecificity of the isomerization reaction are consistent with selective complexation-induced carbon–carbon bond homolysis. The ΔG‡ of catalyzed and uncatalyzed reactions were estimated to be 14.4 and 40.0 kcal/mol, respectively with the computational method, (U)PBE0-D3/def2-TZVPP-SMD(toluene)//(U)B3LYP-D3/def2-SVP. We report this work as the first catalytic example where the complexation-induced bond-weakening effect is quantified through transition state analysis.