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Reactivity of Ir(iii) carbonyl complexes with water: alternative by-product formation pathways in catalytic methanol carbonylation

Elliott, Paul I., Haak, Susanne, Meijer, Anthony J. H. M., Sunley, Glenn J. and Haynes, Anthony (2013) Reactivity of Ir(iii) carbonyl complexes with water: alternative by-product formation pathways in catalytic methanol carbonylation. Dalton Transactions, 42 (47). pp. 16538-16546. ISSN 1477-9226

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Abstract

The reactions of water with a number of iridium(III) complexes relevant to the mechanism for catalytic methanol carbonylation are reported. The iridium acetyl, [Ir(CO)2I3(COMe)]−, reacts with water under mild conditions to release CO2 and CH4, rather than the expected acetic acid. Isotopic labeling and kinetic experiments are consistent with a mechanism involving nucleophilic attack by water on a terminal CO ligand of [Ir(CO)2I3(COMe)]− to give an (undetected) hydroxycarbonyl species. Subsequent decarboxylation and elimination of methane gives [Ir(CO)2I2]−. Similar reactions with water are observed for [Ir(CO)2I3Me]−, [Ir(CO)2(NCMe)I2(COMe)] and [Ir(CO)3I2Me] with the neutral complexes exhibiting markedly higher rates. The results demonstrate that CO2 formation during methanol carbonylation is not restricted to the conventional water gas shift mechanism mediated by [Ir(CO)2I4]− or [Ir(CO)3I3], but can arise directly from key organo-iridium(III) intermediates in the carbonylation cycle. An alternative pathway for methane formation not involving the intermediacy of H2 is also suggested. A mechanism is proposed for the conversion MeOH + CO → CO2 + CH4, which may account for the similar rates of formation of the two gaseous by-products during iridium-catalysed methanol carbonylation.

Graphical abstract: Reactivity of Ir(iii) carbonyl complexes with water: alternative by-product formation pathways in catalytic methanol carbonylation

Item Type: Article
Subjects: Q Science > Q Science (General)
Schools: School of Applied Sciences
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Depositing User: Cherry Edmunds
Date Deposited: 02 Apr 2014 09:55
Last Modified: 02 Apr 2014 09:55
URI: http://eprints.hud.ac.uk/id/eprint/19942

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