title: Fast and reversible insertion of carbon dioxide into zirconocene-alkoxide bonds. A mechanistic study.
abstract: In two consecutive equilibria the compound (Cp*)2Zr(OMe)2 undergoes insertion of CO2 to form the mono- and bis-hemicarbonates. Both equilibria are exothermic but entropically disfavoured. Magnetisation transfer experiments gave kinetic data for the first equilibrium showing that the rate of insertion is overall second order with a rate constant of 3.20 ± 0.12 M(-1) s(-1), which is substantially higher than those reported for other early transition metal alkoxides, which are currently the best homogeneous catalysts for dimethyl carbonate formation from methanol and CO2. Activation parameters for the insertion reaction point to a highly ordered transition state and we interpret that as there being a substantial interaction between the CO2 and the metal during the C-O bond formation. This is supported by DFT calculations showing the lateral attack by CO2 to have the lowest energy transition state.
authors.affiliation: Department of Chemistry, University of the Free State, Bloemfontein 9300, South Africa.
authors.forename: Alice
authors.initials: A
authors.lastname: Brink
authors.forename: Ida
authors.initials: I
authors.lastname: Truedsson
authors.forename: André
authors.initials: A
authors.lastname: Fleckhaus
authors.forename: Magnus T
authors.initials: MT
authors.lastname: Johnson
authors.forename: Per Ola
authors.initials: PO
authors.lastname: Norrby
authors.forename: Andreas
authors.initials: A
authors.lastname: Roodt
authors.forename: Ola F
authors.initials: OF
authors.lastname: Wendt
mesh_terms: D002245:Carbon Dioxide / Q000737:chemistry*; D004146:Dioxanes / Q000737:chemistry*; D007700:Kinetics; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D011789:Quantum Theory; D015040:Zirconium / Q000737:chemistry*
chemical_list: D004146:Dioxanes; D009942:Organometallic Compounds; C023398:Zirconocene dichloride; D002245:Carbon Dioxide; D015040:Zirconium