Influence of Ligand Steric Bulk in the Synthesis of Transition-Metal Borylene Complexes

The differing steric requirements of phenyl and mesityl substituents have been shown to influence reactivity in asymmetric transition-metal haloboryl complexes of the type (η5-C5R5)Fe(CO)2B(X)Ar (R = H, Me; X = Cl, Br; Ar = Ph, Mes). Hence substitution of both halides in PhBCl2 can be achieved by reaction with an excess of the bulky organometallic nucleophile Na[(η5-C5Me5)Fe(CO)2], to generate [(η5-C5Me5)Fe(CO)]2(μ-CO)(μ-BPh) (4c), the first metal complex containing the phenylborylene ligand.