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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

Creator:

Petronilho, Ana; Woods, James A.; Müller-Bunz, Helge; Bernhard, Stefan; Albrecht, Martin;

Institution: Wiley
Subject Keywords: Carbene; C-H activation; Iridium; Mesoionic ligand; Oxidation reactions; Stability;
Region:
Description:

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.

Related: http://dx.doi.org/10.1002/chem.201404776
Suggested citation:

Petronilho, Ana; Woods, James A.; Müller-Bunz, Helge; Bernhard, Stefan; Albrecht, Martin; . () 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 [Online]. Available from: http://www.thehealthwell.info/node/863378 [Accessed: 17th January 2018].

  

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