13C and 19F NMR study of α,β-difluorostyryl derivatives of transition metal carbonylates.: A method of signal assignment based on the carbon-fluorine spin-spin coupling constants

The C-13 and F-19 NMR spectra of Z- and E-isomers of beta-X-substituted alpha,beta-difluorostyrenes (X = F, Cl, CpFe(CO)(2), Re(CO)(5), Re-2(CO)(9)Na) were studied. Direct and long-range (across 1-5 bonds) spin-spin coupling constants and the (C-13-C-12) isotope shifts in the F-19 NMR spectra were determined. The study of the C-13 satellites in the F-19 NMR spectra of substituted difluorostyrenes permitted assignment of the C-13 NMR signals of the vinylic carbon atoms. Similarly, the signals in F-19 NMR spectra were assigned based on coupling constants of fluorine with ipso-carbon. These assignments were found to be in good agreement with the data available from the literature (X = F, CI). The developed approach was applied to the elucidation of the structure of Z-PhCF=CClFe(CO)(2)Cp.