COMBINED STATIC AND DYNAMIC DENSITY-FUNCTIONAL STUDY OF THE TI(IV) CONSTRAINED GEOMETRY CATALYST (CPSIH(2)NH)TIR(+) .1. RESTING STATES AND CHAIN PROPAGATION

The resting state structure of the metallocene-alkyl cation, the coord ination of the olefin to the preferred resting state structure, and th e insertion process of the Ti-constrained geometry catalyst (CpSiH(2)N H)TiR(+) have been studied with density functional theory. A combined static and dynamic approach has been utilized whereby ''static'' calcu lations of the stationary points on the potential surface are meshed w ith first principles Car-Parrinello molecular dynamics simulations. Th e first molecular dynamics simulation specifically addressing the stru cture of a metallocene-alkyl cation is presented showing rapid interco nversion between gamma- and beta-agostic conformations. Complementary static calculations show a small energetic preference for a gamma-agos tic resting state. Coordination of the olefin to the Ti-alkyl resting state is likely to result in the formation of a beta-agostic pi-comple x which is highly favored energetically over other pi-complexes that m ay initially form. The whole propagation cycle was studied from pi-com plex to subsequent x-complex. The propagation barrier corresponds to t he insertion process which was calculated to have a free energy barrie r of Delta G(double dagger) = 24.3 kJ/mol at 300 K. The initial beta-a gostic interactions which stabilize the pi-complex are replaced by alp ha-agostic bonds which stabilize the insertion transition state. A stu dy of the back-side insertion process reveals that it may be competiti ve with the front-side insertion process.