title: Carbon-oxygen bond cleavage with eta9,eta5-bis(indenyl)zirconium sandwich complexes.
abstract: Treatment of the eta9,eta5-bis(indenyl)zirconium sandwich complex, (eta9-C9H5-1,3-(SiMe3)2)(eta5-C9H5-1,3-(SiMe3)2)Zr, with dialkyl ethers such as diethyl ether, CH3OR (R=Et, nBu, tBu), nBu2O, or iPr2O resulted in facile C-O bond scission furnishing an eta5,eta5-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 eta5,eta5-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 eta5,eta5-bis(indenyl)zirconium alkyl hydride intermediate followed by rapid beta-alkoxide elimination. For isolable eta6,eta5-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 eta5,eta5-bis(indenyl)zirconium intermediates that promote rate-determining C-H activation and ultimately C-O bond scission.
authors.affiliation: Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, NY 14853, USA.
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Bradley
authors.forename: Luis F
authors.initials: LF
authors.lastname: Veiros
authors.forename: Doris
authors.initials: D
authors.lastname: Pun
authors.forename: Emil
authors.initials: E
authors.lastname: Lobkovsky
authors.forename: Ivan
authors.initials: I
authors.lastname: Keresztes
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Chirik
mesh_terms: D002244:Carbon / Q000737:chemistry*; D004952:Esters / Q000737:chemistry; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D012680:Sensitivity and Specificity; D013237:Stereoisomerism; D015040:Zirconium / Q000737:chemistry*
chemical_list: D004952:Esters; D009942:Organometallic Compounds; D002244:Carbon; D015040:Zirconium; D010100:Oxygen