Chemical bonding in "early-late" transition metal complexes [(H2N)3M-M'(CO)4] (M = Ti, Zr, Hf; M' = Co, Rh, Ir)

Quantum chemical DFT calculations at the BP86/TZ2P level have been carried out for the complex [HSi(SiH2NH)(3)Ti-Co(CO)(4)], which is a model for the experimentally observed compound [MeSi{SiMe2N(4-MeC6H4)}(3)Ti-Co(CO)(4)] and for the series of model systems [(H2N)(3)M-M'(CO)(4)] (M = Ti, Zr, Hf; M' = Co, Rh, Ir). The Ti-Co bond in [HSi(SiH2NH)(3)Ti-Co(CO)(4)] has a theoretically predicted BDE of D (e) = 59.3 kcal/mol. The bonding analysis suggests that the titanium atom carries a large positive charge, while the cobalt atom is nearly neutral. The covalent and electrostatic contributions to the Ti-Co attraction have similar strength. The Ti-Co bond can be classified as a polar single bond, which has only little pi contribution. Calculations of the model compound (H2N)(3)Ti-Co(CO)(4) show that the rotation of the amino groups has a very large influence on the length and on the strength of the Ti-Co bond. The M-M' bond in the series [(H2N)(3)M-M'(CO)(4)] becomes clearly stronger with Ti < Zr < Hf, while the differences between the bond strengths due to change of the atoms M' are much smaller. The strongest M-M' bond is predicted for [(H2N)(3)Hf-Ir(CO)(4)].