Cyclometalated IrIII Complex Possessing Chiral MIC ligand: Regiospecific sp3 C-H Activation and Asymmetric Transfer Hydrogenation of Ketone

Chemistry. 2024 Nov 27:e202403516. doi: 10.1002/chem.202403516. Online ahead of print.

Abstract

Cyclometalation offers a wide number of organometallic metallacycles showing diverse applications. However, such NHC complexes synthesized via an sp3 C-H bond activation are rare. An iridium(III) complex with a chiral mesoionic N-heterocyclic carbene (MIC) ligand, where the IrIII forms an additional Ir-C bond via a regiospecific sp3 C-H bond activation at the N-methylbenzyl wingtip, was synthesized and characterized. To our best knowledge, this represents the first example of cyclometalated iridium(III) complex possessing a chiral MIC donor ligand. The formation of the complex was followed by 2D correlation NMR spectroscopy and the molecular formula mass was evidenced by ESI-HRMS mass spectrometry. The molecular structure of the IrIII-MIC complex was unambiguously established by the single crystal XRD data. This cyclometalated IrIII complex was employed in the asymmetric transfer hydrogenation of 4-bromoacetophenone, and the complex was successful to transfer chirality to the final alcohol molecules (up to 92 % ee).

Keywords: Asymmetric transfer hydrogenation; Chiral iridium(III) complex; Regiospecific sp3 C−H bond activation; Triazolylidene based MIC-ligand.

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