Excited-state tris(pentafluorophenyl)borane as a strong single-electron oxidant: Photophysical properties and catalysis

Abstract

The photophysical properties and photocatalysis of tris(pentafluorophenyl)borane [B(C6F5)3], known as a strong Lewis acid, were revealed. The excited-state B(C6F5)3 exerts single-electron oxidation capability with an oxidation potential (Ered* = 2.02 V vs SCE) close to those of electronically unbiased toluene derivatives (Eox = 2.01 to 2.29 V). This property was experimentally proven by the direct observation of the radical cation of the toluene dimer by the transient absorption spectroscopy of a mixture of B(C6F5)3 and toluene. In cooperation with a suitable Brønsted base catalyst, B(C6F5)3 catalytically generated benzylic radicals from toluene derivatives under photoirradiation for subsequent carbon-carbon bond-forming reactions.

Keywords

• Photooxidant
• Borane
• Radical cation
• Transient absorption spectroscopy
• Carbon-carbon bond formation