Analysis of bonding in cyclopentadienyl transition-metal boryl complexes

Analysis of the bonding in transition-metal boryl complexes of the type [(C5R5)M(CO)(2)-BX2] has been carried out by density functional methods, to quantify the relative contributions to the metal boryl linkage from ionic and covalent interactions. Covalent (orbital) terms account for 60-70% of the overall attractive interaction between metal and boryl fragments, with sigma donation from the boryl ligand overwhelmingly predominating over pi back-donation even in the most favorable cases (e.g. 84.1:15.8 and 81.9:18.0 for CpFe(CO)(2)BH2 and CpFe(CO)(2)B(C6F5)(2), respectively).