Fluxional {eta}{sup 3}-allyl derivatives of anso-scandocenes and anso-yttrocene. Measurements of the barriers for the {eta}{sup 3} to {eta}{sup 1} process as an indicator of olefin binding energy to d{sup 0} metallocenes
- California Inst. of Tech., Pasadena, CA (United States). Arnold and Mabel Beckman Labs. of Chemical Synthesis
Variable-temperature {sup 1}H NMR spectroscopy indicates fluxional behavior for a number of group 3 metallocene allyl complexes. Spectral simulations and line shape analyses for the variable-temperature spectra indicate an allyl rearrangement mechanism involving rate-determining carbon-carbon double-bond dissociation from the metal center, i.e., an {eta}{sup 3} to {eta}{sup 1} change in coordination. Activation barriers to olefin dissociation have been determined for ({eta}{sup 5}-C{sub 5}Me{sub 5}){sub 2}Sc({eta}{sup 3}-C{sub 3}H{sub 5}), meso-Me{sub 2}Si({eta}{sup 5}-3-CMe{sub 3}-C{sub 5}H{sub 3}){sub 2}Sc({eta}{sup 3}-C{sub 3}H{sub 5}), meso-Me{sub 2}Si[{eta}{sup 5}-2,4-(CHMe{sub 2}){sub 2}C{sub 5}H{sub 2}]{sub 2}Sc({eta}{sup 3}-C{sub 3}H{sub 5}), meso-Me{sub 2}Si{l_brace}{eta}{sup 5}-3-[2-(2-Me)-adamantyl]-C{sub 5}H{sub 3}{r_brace}{sub 2}Sc({eta}{sup 3}-C{sub 3}H{sub 5}), meso-Me{sub 2}Si{l_brace}{eta}{sup 5}-3-[2-(2-Me)-adamantyl]-C{sub 5}H{sub 3}{r_brace}{sub 2}Y({eta}{sup 3}-C{sub 3}H{sub 5}), rac-Me{sub 2}Si[{eta}{sup 5}-2,4-(CHMe{sub 2}){sub 2}-C{sub 5}H{sub 2}]{sub 2}Sc({eta}{sup 3}-C{sub 3}H{sub 5}), and R-(C{sub 20}H{sub 12}O{sub 2})Si({eta}{sup 5}-2-SiMe{sub 3}-4-CMe{sub 3}-C{sub 5}H{sub 2}){sub 2}Sc({eta}{sup 3}-C{sub 3}H{sub 5}): {Delta}G{sup {double_dagger}} = 11--16 kcal/mol at ca. 300--350 K. Donor solvents do not significantly affect the rate of olefin dissociation. A second rearrangement mechanism that involves 180{degree} rotation of the {eta}{sup 3}-C{sub 3}H{sub 5} rotation is generally more than 1 order of magnitude faster than olefin dissociation for a given meso metallocene. The data do not allow unambiguous assessments of the mechanism(s) for the fluxional behavior for the allyl derivatives of the racemic metallocenes. An X-ray structure determination for rac-Me{sub 2}Si[{eta}{sup 5}-C{sub 5}H{sub 2}-2,4-(CHMe{sub 2}){sub 2}]{sub 2}Sc({eta}{sup 3}-C{sub 3}H{sub 5}) has been carried out.
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- FG03-85ER13431
- OSTI ID:
- 343703
- Journal Information:
- Organometallics, Journal Name: Organometallics Journal Issue: 8 Vol. 18; ISSN ORGND7; ISSN 0276-7333
- Country of Publication:
- United States
- Language:
- English
Similar Records
Racemic-meso interconversion for ansa-scandocene and ansa-yttrocene derivatives. Molecular structures of rac-{l_brace}Me{sub 2}Si[{eta}{sup 5}-C{sub 5}H{sub 2}-2,4-(CHMe{sub 2}){sub 2}]{sub 2}{r_brace}ScCl {center_dot} LiCl(THF){sub 2}, [meso-{l_brace}Me{sub 2}Si[{eta}{sup 5}-C{sub 5}H{sub 2}-2,4-(CHMe{sub 2}){sub 2}]{sub 2}{r_brace} Y({mu}{sub 2}-Cl)]{sub 2}, and meso-{l_brace}Me{sub 2}Si[{eta}{sup 5}-C{sub 5}H{sub 2}-2,4-(CHMe{sub 2}){sub 2}]{sub 2}{r_brace}Zr(NMe{sub 2}){sub 2}
Double-insertion reaction of alkynes with [CP{sup {prime}}{sub 2}ZrMe]{sup +}: Formation of an unusual distorted {eta}{sup 5}-pentadienyl ligand