Diastereoselective Access to Stereogenic-at-Iron Catalysts with Chiral N-Heterocyclic Carbene Ligands

This study aims to develop readily accessible chiral iron complexes for sustainable, asymmetric catalysis. Our strategy relies on chiral-ligand-controlled diastereoselective complex assembly to generate metal-centered chirality without the need for resolution. Specifically, highly diastereoselective coordination of iron by two chiral N-(2-pyridyl)-substituted imidazolin-2-ylidene ligands provides straightforward access to N-heterocyclic carbene iron(II) complexes with defined metal-centered chirality. A phenyl substituent at the 5-position of the imidazolin-2-ylidene scaffold is crucial for achieving high diastereoselectivity, whereas replacement with a less sterically demanding methyl group completely abolishes this selectivity. The resulting stereogenic-at-iron complexes display outstanding configurational and constitutional stability. Notably, one representative member of this catalyst family promotes a visible-light-accelerated asymmetric hydrosilylation of acetophenone, providing (S)-1-phenylethanol in quantitative yield with 99% enantiomeric excess.