Half‐Sandwich Manganese Complex Bearing Fused Oxazoline‐NHC Ligand: Conformational Analysis and Evaluation in Asymmetric Ketone Hydrosilylation

Half-sandwich Mn(I) complex bearing chiral N-heterocyclic carbene ligand exists in solution as a mixture of two conformers exhibiting markedly different IR spectra. According to DFT calculations these unusual spectroscopic properties may be caused by the influence of attractive π(C=C)⋅⋅⋅π*(C≡O) and σ(C−H)⋅⋅⋅π*(C≡O) interligand interactions on ν_CO band frequencies.

Abstract

The first manganese complex bearing a chiral N-heterocyclic carbene (NHC) ligand was prepared and studied by spectroscopic methods and X-ray diffraction. While IR spectroscopy revealed the existence of two isomers in solution with distinct ν_CO band patterns, DFT calculations indicated that these isomers correspond to rotamers around the Mn−NHC bond and their different spectroscopic properties were rationalized by the occurrence of attractive π(C=C)⋅⋅⋅π*(C≡O) or σ(C−H)⋅⋅⋅π*(C≡O) intramolecular interligand interactions. The evaluation of this complex in catalytic hydrosilylation of acetophenone using Ph₂SiH₂ under UV irradiation led to the formation of the corresponding (R)-alcohol with low enantioselectivity.

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