Reactions of tricarbonyl(η-hexamethylbenzene)chromium derivatives with nitrosonium and benzenediazonium ions: reversible oxidation versus nitrosyl- or areneazo-complex formation

Abstract

The complexes [Cr(CO)₂L(η-C₆Me₆)][L = PPh₃, PMePh₂, PMe₂Ph, P(OPh)₃, or P(OMe)₃] react with [NO][PF₆] to afford [Cr(CO)L(η-C₆Me₆)(NO)][PF₆], (I), and [Cr(CO)₂(η-C₆Me₆)(NO)][PF₆] whereas [PhN₂][PF₆] yields paramagnetic [Cr(CO)₂L(η-C₆Me₆)][PF₆](L = PPh₃, PMePh₂, or PMe₂Ph) or [Cr(CO)L(η-C₆Me₆)(N₂Ph)][PF₆] and [Cr(CO)₂(η-C₆Me₆)(N₂Ph)][PF₆][L = P(OMe)₃ or P(OPh)₃]. Electrochemical studies confirm that oxidation of [Cr(CO)₂L(η-C₆Me₆)] to [Cr(CO)₂L(η-C₆Me₆)]⁺ is a reversible one-electron process. The factors determining whether [NO]⁺ or [PhN₂]⁺ oxidise organometallic complexes or cause substitution are discussed on the basis of the electrochemical and preparative results, and a general mechanism for the reactions of these ions with organotransition-metal complexes is proposed.