C-D0 (D0 = π-donor, F) cleavage in H2C=CH(D0) by (Cp2ZrHCl)n:: Mechanism, agostic fluorines, and a carbene of Zr(IV)

Consistent with the C-O cleavage behavior of vinyl ethers, vinyl fluoride reacts with Cp2ZrHCl to give Cp2ZrFCl and C2H4 as primary; products. DFT (B3PW91) calculations show this reaction to be highly exoenergetic (-55 kcal/mol), and reveal a sigma -bond metathesis mechanism to be unfavorable compared to a Zr-H addition across the C=C bond, with regiochemistry placing F on C-beta of the resulting fluoroethyl ligand. beta -F elimination (onto Zr)then completes the reaction. There is no eta (2)-olefin intermediate on the reaction path. DFT calculations seeking the energy and: structure of the two carbenes Cp2ZrHCl[CF(CH3)] and Cp2ZrFCl[CH(CH3)] are also described.