Masked Radicals: Iron Complexes of Trityl, Benzophenone, and Phenylacetylene

We report the first Fe–CPh₃ complex and show that the long Fe–C bond can be disrupted by neutral π-acceptor ligands (benzophenone and phenylacetylene) to release the triphenylmethyl radical. The products are formally iron­(I) complexes, but X-ray absorption spectroscopy coupled with density functional and multireference ab initio calculations indicates that the best description of all the complexes is iron­(II). In the formally iron­(I) complexes, this does not imply that the π-acceptor ligand has radical character, because the iron­(II) description arises from doubly occupied frontier molecular orbitals that are shared equitably by the iron and the π-acceptor ligand, and the unpaired electrons lie on the metal. Despite the lack of substantial radical character on the ligands, alkyne and ketone fragments can couple to form a high-spin iron­(III) complex with a cyclized metalladihydrofuran core.