The compound [Ph 2N 3C 2(C 3F 7) 2]HgCH 3 was synthesized from Na[Ph 2N 3C 2(C 3F 7) 2] and CH 3- HgCl. In solution, it exists as a mixture of two isomers that interconvert slowly on the NMR time scale. Both isomers feature a η 1-Ph 2N 3C 2(C 3F 7)2 ligand. In the asymmetrical one, the CH 3Hg group is bonded to one of the two terminal nitrogen atoms. In the more stable symmetrical isomer, [PhN=C(C 3F 7)] 2NHgCH 3, mercury is attached to the central nitrogen atom. It is this isomer that crystallizes and that was characterized by X-ray diffraction. Thermodynamic parameters for the CH 3Hg shift reaction were obtained by DNMR spectroscopy. 19F NMR spectra were analyzed. A metallotropic rearrangement was not observed in [Ph 2N 3C 2(C 3F 7) 2]AuPPh 3.