Theoretical description of bonding in cis-W(CO)(4)(piperidine)(2) and its dimer

The gradient-corrected DFT calculations were applied to characterize the bonding in the cis-W(CO)(4)(piperidine)(2) complex and its dimer. The Nalewajski-Mrozek bond order analysis, the Ziegler-Rauk bond-energy partitioning and Natural Orbitals for Chemical Valence (NOCV's) were applied in a description of the electronic structure of cis-W(CO)(4)(piperidine)(2). The results indicate that the metal-carbon bond trans to piperidine is stronger than that in the cis position, as a result of an increase in both, the ligand--> metal donation and metal --> ligand pi-back-bonding; this implies a weakening of the carbon-oxygen bond. In the dimeric complex, modeling the interactions in the solid state, the C-O bond is further weakened resulting in the lowering the CO stretching frequencies, observed experimentally by Braunstein et al. (Angew. Chem. Int. Ed. (2004), 43:5922-5925).