The reaction of dioxygenyl salts with 13CO: Formation of F13C(O)13C(O)F

Oxalyl fluoride has been prepared directly in high yield from CO and the dioxygenyl salts O2[BF4] or O2[AsF6]. The formation of intermediate FCO radicals is indicated by differences in reaction rates and the observation of FC(O)OOC(O)F as a by-product. From the analysis of the NMR spectra of 13C enriched FC(O)C(O)F including selective irradiation experiments positive signs for both the FF (+50.6 Hz) and CC (+126.1 Hz) coupling constants are deduced. From the temperature dependency of 3J(FF), values of +70 Hz and −10 Hz are estimated for the trans- and cis-rotamers, respectively.