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 (η 5 -C 5 R 5 )Fe(CO) 2 B(X)Ar (R = H, Me; X = Cl, Br; Ar = Ph, Mes). Hence substitution of both halides in PhBCl 2 can be achieved by reaction with an excess of the bulky organometallic nucleophile Na[(η 5 -C 5 Me 5 )Fe(CO) 2 ], to generate [(η 5 -C 5 Me 5 )Fe(CO)] 2 (μ-CO)(μ-BPh) ( 4c ), the first metal complex containing the phenylborylene ligand.