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Issue 5, 2005
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IrII(ethene): Metal or carbon radical? Part II: Oxygenation via iridium or direct oxygenation at ethene?

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Abstract

Treatment of [(Me3tpa)IrII(ethene)]2+ (Me3tpa = N,N,N-tri(6-methyl-2-pyridylmethyl)amine) (12+) with dioxygen in weakly coordinating solvents results in formation of [(Me3tpa)IrIII(ethene)(superoxo)]2+ (4a2+). In the presence of DMPO (DMPO = 5,5-dimethyl-2-pyrrolidine-1-oxide) DMPO is substituted for ethene, and subsequently oxidized to DMPOX by the superoxo fragment to give [(Me3tpa)IrIII(DMPOX)]2+ (72+; DMPOX = 5,5-dimethyl-2-pyrrolidone-1-oxide). In acetonitrile, in the absence of DMPO, oxygenation of 12+ to [(Me3tpa)IrIII(formylmethyl)(MeCN)]2+ (22+) is observed. In the presence of DMPO the formation of 22+ and 72+ is competing. Oxygenation of 12+ to 22+ may proceed via4a2+, involving an insertion mechanism at the metal. However, a mechanism based on olefin ligand non-innocence seems a reasonable alternative. This involves formation of acetonitrile adduct [(Me3tpa)Ir(ethene)(MeCN)]2+ (32+), which has a significant metalla-ethyl radical (IrIII–CH2CH2˙) character, allowing attack of 3O2directly at the ethene ligand. Both pathways are discussed on the basis of experimental observations and DFT geometry optimizations.

Graphical abstract: IrII(ethene): Metal or carbon radical? Part II: Oxygenation via iridium or direct oxygenation at ethene?

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Article information


Submitted
24 Nov 2004
Accepted
13 Jan 2005
First published
26 Jan 2005

Dalton Trans., 2005, 979-984
Article type
Paper

IrII(ethene): Metal or carbon radical? Part II: Oxygenation via iridium or direct oxygenation at ethene?

D. G. H. Hetterscheid, M. Bens and B. de Bruin, Dalton Trans., 2005, 979
DOI: 10.1039/B417766E

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