| Abstract |
The bonding of pyrrolyl ligands (pyr ) in group-4 metal complexes, [M(pyr )Cl-3], is studied by means of DFT/B3LYP calculations with a VDZP basis set. Two metals (M = Ti, Hf) and two pyrrolyl ligands are addressed, pyr = pyrrolyl (pyr), and 2,5-dimethylpyrrolyl (dmp). The study allowed the characterization of the pi-pyr complexes with a eta(5) coordination of this ligand, the a complexes with the pyr bonding established by the nitrogen lone pair, and the transition states for the interconversion between the two isomers. A comparative analysis of the pyr bonding to the metal in all the species is provided, as well as a detailed study of the mechanism for the interconversion between the two pyr coordination modes. This is a slippage process without significant folding of the pyr ring and the activation energies obtained (E-a < 9 kcal mol(-1)) suggest the possible fluxionality between the two coordination modes, in solution. Calculated pyr -M bond enthalpies show an increase in the bond strength going down the group, allowing a rationalization of the differences in stability of the two coordination modes observed for the various metals and, consequently, of the associated ring slippage process. |
