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Iridium Complexes Containing Mesoionic C Donors: Selective C(sp3)-H versus C(sp2)-H Bond Activation, Reactivity Towards Acids and Bases, and Catalytic Oxidation of Silanes and Water
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chem.201404776_ms_revsd.pdf | 1.59 MB |
Date Issued
24 November 2014
Date Available
10T03:00:19Z October 2015
Abstract
Metalation of a C2-methylated pyridylimidazolium salt with [IrCp*Cl2]2 affords either an ylidic complex, resulting from C(sp3)[BOND]H bond activation of the C2-bound CH3 group if the metalation is performed in the presence of a base, such as AgO2 or Na2CO3, or a mesoionic complex via cyclometalation and thermally induced heterocyclic C(sp2)[BOND]H bond activation, if the reaction is performed in the absence of a base. Similar cyclometalation and complex formation via C(sp2)[BOND]H bond activation is observed when the heterocyclic ligand precursor consists of the analogous pyridyltriazolium salt, that is, when the metal bonding at the C2 position is blocked by a nitrogen rather than a methyl substituent. Despite the strongly mesoionic character of both the imidazolylidene and the triazolylidene, the former reacts rapidly with D+ and undergoes isotope exchange at the heterocyclic C5 position, whereas the triazolylidene ligand is stable and only undergoes H/D exchange under basic conditions, where the imidazolylidene is essentially unreactive. The high stability of the Ir[BOND]C bond in aqueous solution over a broad pH range was exploited in catalytic water oxidation and silane oxidation. The catalytic hydrosilylation of ketones proceeds with turnover frequencies as high as 6 000 h−1 with both the imidazolylidene and the triazolylidene system, whereas water oxidation is enhanced by the stronger donor properties of the imidazol-4-ylidene ligands and is more than three times faster than with the triazolylidene analogue.
Sponsorship
European Research Council
Science Foundation Ireland
Other Sponsorship
National Science Foundation
Type of Material
Journal Article
Publisher
Wiley
Journal
Chemistry - A European Journal
Volume
20
Issue
48
Start Page
15775
End Page
15784
Copyright (Published Version)
2014 Wiley
Language
English
Status of Item
Peer reviewed
This item is made available under a Creative Commons License
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