A Phosphine-Coordinated Boron-Centered Gomberg-Type Radical
Résumé
The P-coordinated boryl radical [Ph\textlessinf\textgreater2\textless/inf\textgreaterP(naphthyl)BMes]. (Mes=mesityl) was prepared by (electro)chemical reduction of the corresponding borenium salt or bromoborane. Electron paramagnetic resonance (EPR) analysis in solution and DFT calculations indicate large spin density on boron (60-70%) and strong P-B interactions (P→B σ donation and B→P negative hyperconjugation). The radical is persistent in solution and participates in a Gomberg-type dimerization process. The associated quinoid-type dimer has been characterized by single-crystal X-ray diffraction. Radical action: A P-coordinated boryl radical with large spin density at the boron center is reported. The structure of the radical has been analyzed by EPR spectroscopy and using DFT calculations. The radical is found to undergo dimerization by a Gomberg-type dimerization process.