Synthesis and characterization of a planar chiral and chiral-at-metal ruthenium N-heterocyclic carbene complex

This report describes the conversion of the neutral planar chiral arene-tethered complex [Ru(η⁶:η¹-Me₂NC₆H₄C₆H₄PCy₂)Cl₂ (1), into [Ru(η⁶: η¹-Me₂NC₆H₄C₆H₄PCy₂)(1,3-dibutylimidazol-2-ylidene)Cl]BF₄ (2) via silver transmetallation. The cationic title complex is also chiral-at-metal, and forms stereoselectively as a result of the directing effect of the arene-tethered ligand. The structure in solution and in the solid state was examined; a puckered distortion of the η⁶-arene was noted in the crystal structure, along with a hindered rotation of the NHC in solution. As a comparison to the previously reported phosphine analogues, the dication derived from 2 was used to catalyze the asymmetric Diels-Alder reaction of methacrolein and cyclopentadiene.