Selective Oxidation of (Porphyrinato)iridium(III) Arylethyls by Nitroxide:  Evidence for Stabilization of Carbon-Centered Ir−CH₂−CHR^• Radicals by Iridium

Abstract

(Arylethyl)iridium(III) porphyrins were oxidized selectively with excess 2,2,6,6-tetramethylpiperidinoxy (TEMPO) at the benzylic positions to yield (2-aryl-2-oxoethyl)iridium porphyrins. Other alkyl- and PhCH 2 CH 2 CH 2 -substituted iridium porphyrins did not react or gave complex mixtures and low yields of iridium methyl. The proposed intermediate of the carbon-centered Ir III (CH 2 CHR • ) radical is probably stabilized by the β iridium center, allowing the (slipped) olefin metalloradical complex Ir II (CH 2 CHR) as a reasonable resonance structure.