Formation of an Unexpected Organometallic Mercury Compound in a Palladium-Catalyzed Reaction

The new and unexpected organometallic mercury compound 3 has been identified in the palladium-catalyzed reaction
between
bis­(ferrocenyl)mercury (1) and dimethylacetylenedicarboxylate
(2) along with the expected dimethyl-(Z)-2,3-di­(ferrocenyl)-2-butenedioate (4) and biferrocene
(5). Organometallic mercury complex 3 resulted
from syn-addition of 1 to 2 equiv of 2. Complex 3 has been characterized using NMR
spectroscopy, while its structure was determined by X-ray crystallography.
Complex 3 represents a rare example of an organomercury
compound in which a mercury ion is coordinated to two vinylic fragments.
Accurate, low-temperature experimental data for the crystal structure
of 5 is also reported.