Carbon-oxygen bond cleavage with η9,η5-bis(indenyl)zirconium sandwich complexes

Treatment of the eta(9), eta(5)-bis(indenyl)zirconium sandwich complex, (eta(9)-C9H5-1,3-(SiMe3)(2))(eta(5)-C9H5-1,3-( SiMe3)(2))Zr, with dialkyl ethers such as diethyl ether, CH3OR (R = Et, Bu-n, Bu-t), (Bu2O)-Bu-n, or (Pr2O)-Pr-i resulted in facile C-O bond scission furnishing an eta(5), eta(5)-bis(indenyl)zirconium alkoxy hydride complex and free olefin. In cases where ethylene is formed, trapping by the zirconocene sandwich yields a rare example of a crystallographically characterized, base-free eta(5), eta(5)-bis(indenyl)zirconium ethylene complex. Observation of normal, primary kinetic isotope effects in combination with rate studies and the stability of various model compounds support a mechanism involving rate-determining C-H activation to yield an eta(5), eta(5)-bis(indenyl)zirconium alkyl hydride intermediate followed by rapid beta-alkoxide elimination. For isolable eta(6), eta(5)-bis(indenyl)zirconium THF compounds, thermolysis at 85 degrees C also resulted in C-O bond cleavage to yield the corresponding zirconacycle. Both mechanistic and computational studies again support a pathway involving haptotropic rearrangement to eta(5), eta(5)-bis(indenyl)zirconium intermediates that promote rate- determining C-H activation and ultimately C-O bond scission.