Evidence for a boride-borylene-ligand-tautomerism leading to a remote C-C-bond and concomitant boryl ligand formation

The formation of a rhodium pincer-type complex with a boron-based donor ligand and its reactivity are reported. The starting complex contains a formal borylene moiety, stabilised by two pyridine substituents. Quantum chemical investigations indicate the possibility of deprotonation of the central donor group of the type py2BH in this complex. Efforts to isolate the resulting formal boride species, however, led to a boryl complex with concomitant formation of a new C–C-bond, accompanied by a loss of aromaticity. Mechanistic investigations indicate the presence of tautomerism between two deprotonated species, giving rise to a ligand-stabilised boride and a ligand-stabilised borylene motif.