Main-group organometallic reagents based on environmentally benign and biocompatible metals such as magnesium and bismuth are increasingly being adopted in chemical synthesis for novel bond activation events competitive with transition metals. Due to their electropositive nature, the majority of reactive organo-magnesium and -bismuth reagents are supported by chelating, anionic ligands based on electronegative elements for persistent complexation. This strategy has resulted in highly potent organomagnesium reagents for redox-invariant catalysis. However, the recent stabilization of low valent M(I) and M(0) complexes of magnesium and its lighter counterpart, beryllium, suggests that metal-based redox transformations in <i>s</i>-block chemistry is possible, but require a reevaluation of ligand stabilization strategies. Due to their electronically-flexible nature and potential for stabilizing sub-valent complexes, the utilization of neutral carbon-based donor ligands such as carbenes and carbones is on the rise for stabilizing unusual bonding in main group element complexes. This presentation highlights the carbene-mediated stabilization of diverse magnesium reagents including cationic monomeric Grignard reagents, thermally-stable 2-phosphaethynolates for P-atom transfer, redox-non-innocent complexes with unusual multiple bonding, and amidoborane compounds for hydrogen storage. A similar strategy, involving the use of C(0) donor ligands such as carbodiphosphoranes and carbodicarbenes, has also been employed in the stabilization of catalytically relevant bismaalkene and bismuth hydride complexes. These strategies have also enabled the isolation of electronically diverse magnesium and bismuth cations, whose charge-separated nature imbue unique reactivities due to their enhanced electrophilicity.

Carbenes and carbones as mediators for the cationization of magnesium and bismuth complexes

ACS Spring 2022

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