Spectroscopic Studies on Organometallic Compounds. V. Fluorine Nuclear Magnetic Resonance Spectra of Some Perfluoroalkyl and Perfluoroacyl Metal Compounds

Abstract

The ¹⁹F nuclear magnetic resonance spectra of a variety of fluorocarbon derivatives of metals are reported. A large shift to low field is found for the absorption by a CF₂ group bonded directly to manganese, rhenium, iron, or cobalt. When a carbonyl group is interposed between the transition metal and the CF₂ group, or when a CF₂ group is bonded to tin or phosphorus, no large shifts of the fluorine resonances to low fields are observed. It is suggested that these magnetic screening effects are related to the presence in the transition metal derivatives of low‐lying excited states in the bonds between the metals and the carbon atoms of the α—CF₂ groups, with the result that the paramagnetic contribution to the screening constants of the fluorine nuclei is substantially increased.