Isolated Carbon(I) Species Featuring a Carbone Cation Radical

Abstract

Carbynes, characterized by radical and carbene attributes, possess three non-bonding electrons and have garnered significant scientific interest. The high reactivity and complex hybridization of valence orbitals in carbynes have impeded the isolation of free carbon(I) species, presenting a substantial challenge in carbon chemistry. Carbodicarbenes are divalent carbon (0) species with two electron lone-pairs, which are in principle capable of losing an electron to generate a radical cation C(I), a species containing three non-bonded electrons, similar to the frontier orbital of a carbyne without vacant orbital. Herein, we describe the isolation of a crystalline cation radical C(I) as [1-CDC]^•+, prepared by a novel approach involving single electron transfer (SET) between carbodicarbene and nitro-aromatic compound to generate stable radical ionic pair. The electron paramagnetic resonance (EPR) and X-ray crystallography with quantum chemical analysis shows that the unpaired electron of [1-CDC]^•+ resides in the p(π) AO of secondary carbon with some delocalization to the NHC ligands. Exploring the reactivity of this novel C(I) cation radical revealed its capacity to mediate a variety of C-O and C-C cross-coupling reactions with electron-deficient aryl halides. These findings not only expand the understanding of carbon(I) radical chemistry but also open new avenues for new methodologies in organic synthesis and catalysis via radical manifold.