C−N Bond Activation and Ring Opening of a Saturated N‐Heterocyclic Carbene by Lateral Alkali‐Metal‐Mediated Metalation

Abstract

Combining alkali-metal-mediated metalation (AMMM) and N-heterocyclic carbene (NHC) chemistry, an ovel CÀNb ond activation and ring-opening process is described for these increasingly important NHC molecules, which are generally considered robust ancillary ligands.Here, mechanistic investigations on reactions of saturated NHC SIMes (SIMes = [DC{N(2,4,6-Me 3 C 6 H 2 )CH 2 } 2 ]) with Group 1 alkylb ases suggest this destructive process is triggered by lateral metalation of the carbene.E xploiting co-complexation and trans-metal-trapping strategies with lower polarity organometallic reagents (Mg(CH 2 SiMe 3 ) 2 and Al(TMP)iBu 2 ), key intermediates in this process have been isolated and structurally defined.

Alkali-Metal-Mediated Synergistic Effects in Polar Main Group Organometallic Chemistry

“…Rather than attack the NHC backbone, one of the aromatic bound methyl groups is metalated, with the aluminum reagent trapping the resulting carbanion to yield an aluminate center, while the lithium migrates to the "normal" C2 carbene position in 212 (Scheme 133). 258 An alkyllithium base on its own forces ring opening of the carbene ring (213), with the mechanism believed to involve metalation of the aromatic bound methyl group prior to ring cleavage, emphasizing the synergistic relationship between lithium and aluminum in the metalation of SIMes.…”