13C and19F 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

Abstract

The f3C and 19F NMR spectra of Z-and E-isomers ofl~-X-substituted cq[3-difluorostyrenes (X = F, CI, CpFe(CO) 2, Re(CO)s, Re2(CO)gNa) were studied. Direct and long-range (across I--5 bonds) spin-spin coupling constants and the (13C--12C) isotope shifts in the I~ NMR spectra were determined. The study of the 13C satellites in the tgF NMR spectra of substituted difluorostyrenes permitted assignment of the t3C NMR signals of the vinylic carbon atoms. Similarly, the signals in 19F NMR spectra were assigned based on coupling constants of fluorine with ipso-earbon. 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=CCIFe(CO)~Cp.