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 1477-9226Metadata only available from this repository.
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
|Subjects:||Q Science > Q Science (General)|
|Schools:||School of Applied Sciences|
|Depositing User:||Cherry Edmunds|
|Date Deposited:||02 Apr 2014 09:55|
|Last Modified:||02 Apr 2014 09:55|
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