295359-20-5Relevant academic research and scientific papers
Measurement of barriers for alkene dissociation and for inversion at zirconium in a d0 zirconium-alkyl-alkene complex
Casey, Charles P.,Carpenetti II, Donald W.
, p. 3970 - 3977 (2000)
The β-allyl zirconacyclobutane complex Cp*2Zr[CH2CH(CH2CH double bond CH2)CH2] (7) reacted rapidly with B(C6F5)3 in CD2Cl2 at -78 °C to form the zwitterionic do zirconium(IV) chelate complex Cp*2Zr[η1,η2-CH2CH[CH2B (C6F5)3]CH2CH double bond CH2] (2a and 2b). Low-temperature 1H, 13C, TOCSY1D, and NOESY1D NMR spectroscopy of 2 established the bonding of the tethered alkene to the do metal center. A dynamic NMR study of the interconversion of 2a and 2b allowed measurement of the alkene dissociation energy (ΔG? = 10.5 (2a to 2b) and 10.3 (2b to 2a) kcal mol-1), but the complex decomposed before the barrier for site epimerization at the zirconium center could be determined. Reaction of 7 with [(C6H5)2(CH3)NH][B (C6F5)4] led to the formation of two isomeric do zirconium(IV)-alkyl-alkene chelates Cp*2Zr[η1, η2-CH2CH(CH3)CH2CH double bond CH2][B(C6F5)4] (8a and 8b). This more thermally stable zirconium-alkyl-alkene complex allowed the measurement of barriers associated with decomplexation of the alkene (ΔG? = 10.7 and 11.1 kcal mol-1) and site epimerization at the zirconium center (ΔG? = 14.4 kcal mol-1) by line shape analysis of variable-temperature 1H and 13C NMR spectra.
