Preparation and Structural Characterization of Transition Metal Complexes Featuring the Ferrocenyl(bromo)boryl Ligand^†

Transition metal complexes that feature the ferrocenyl(bromo)boryl ligand, −B(Fc)Br, were prepared utilizing salt-elimination and B−Br bond oxidative addition strategies. The stabilizing interaction that causes bending of the boron atom toward the ferrocenyl iron center in the FcBBr2 precursor (1) weakens upon coordination of boron to the [(η5-C5R5)(OC)2Fe] and trans-[(Cy3P)2PtBr] fragments. The efficient π-back-bonding capability of the latter is reflected in the absence of any Fe−B interaction in crystalline trans-[(Cy3P)2Pt(Br){B(Fc)Br}] (7), the first platinum haloboryl complex featuring a non-heteroatom-stabilized boryl ligand to be fully characterized and structurally authenticated. In the half-sandwich complexes [(η5-C5R5)(OC)2Fe{B(Fc)Br}] (R = H, 2; R = Me, 3) different relative orientations of the [(η5-C5R5)(OC)2Fe] and −B(Fc)Br groups are accompanied by different degrees of bending within the boryl ligand. The sensitivity of this parameter to the electronic environment at boron offers an indirect qualitative estimation of the π-bonding component of the TM−B bond.