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 (eta(5)-C5R5)-Fe(CO)(2)B(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[(eta(5)-C5Me5)Fe(CO)(2)], to generate [(eta(5)-(CMe5)-Me-5)Fe(CO)](2)(mu-CO)(mu-BPh) (4c), the first metal complex containing the phenylborylene ligand.