Redox-Active BIAN-Based Iron Complexes in Catalysis

alpha-Diimine ligands have contributed extensively to the coordination chemistry of the majority of the transition metals; bis(arylimino)acenaphthene ligands (BIANs) have been widely studied and found to offer great versatility in their application as supporting ligands in catalytic transformations. In recent years, BIAN-based iron complexes have proven effective in mediating a number of reductive transformations which includes hydrosilylation, hydroboration and hydrogenation chemistries. This review highlights the most recent contributions to the field. In our initial 2015 communication, we disclosed that the arene-capped Fe(0) species (Ar)BIAN-Fe(toluene) mediates aldehyde and ketone hydrosilylation with exceptional activity under solvent-free conditions. This led us to the discovery that such systems were capable of the hydrosilylation of imines and esters, the hydroboration of imines, aldehydes, ketones, alkenes, and alkynes and even the ring-opening polymerization of raclactide. Spectroscopic and computational studies have firmly established the importance of redox non-innocence in BIAN complexes and detailed mechanistic studies have revealed the importance of spin-state-crossing in catalysis. Although this work represents only a small component of advances in iron catalysis, our efforts have proven influential in Fe-based approaches to reductive transformations and is likely to continue to inform the design of Fe-based catalysts.