Alternatives to the CO Ligand: Coordination of the Isolobal Analogues BF, BNH2, BN(CH3)2, and BO− in Mono- and Binuclear First-Row Transition Metal Complexes

Why are ligands BE (BF, BO−, BNR2) so rare in organometallic chemistry? They are isolobal to CO and coordinate through the boron atom. Are they, therefore, unstable? Certainly not. We show, by means of density functional theory, that transition metal–BE complexes are thermodynamically stable, viable targets for synthetic chemistry. However, the mononuclear [M(CO)n(BE)] complex may suffer from a low kinetic stability. Steric and electronic effects make this problem much less severe in binuclear metal complexes, such as [Mn2(Cp)2(CO)4(BE)] and [Fe2(CO)8(BE)] (see right: E = F, O, NR2).