Application of scalar 13C, 19F couplings between carbonyl carbons and aromatic fluorine to investigation of conformation of chelate phosphitodicarbonylchromium and dicarbonyl(phosphine) chromium complexes of fluorobenzenes

Abstract

The 13C NMR spectra of chelate dicarbonyl-(η 6-2,5-difluorobenzyl)- and −[η 6-2-(2- or 4-fluorophenyl)ethyl]-diphenylphosphito-chromiums as well as those of dicarbonyl(triphenylphosphine)chromium complexes of fluorobenzene and its meta and para substituted (Me and NMe 2) derivatives have been reported. Coupling constants between carbonyl carbons and aromatic fluorine were used for determining the chromium tripod conformation. It was found that in chelate complexes the conformation depends on the length of the arene-metal bridge, on the ability of the arene substituent to stabilize the eclipsed conformation and on the steric interaction between the phosphorus ligand and the ring substituent. The two latter factors appeared also to be of great relevance to conformational equilibrium considerations concerning dicarbonylphosphinechromium complexes.