The alkyne-anion promoted ring-contraction of hexachlorotropone: synthesis and structure of [trimethylsilyl(pentachlorobenzoyl)ethyne]-hexacarbonyldicobalt

The reaction of hexachlorotropone with trimethylsilylethynyl-lithium leads to contraction of the seven-membered ring via a semibenzilic acid rearrangement to yield pentachlorophenyl trimethylsilylethynyl ketone, 4. Treatment of 4 with dicobalt octacarbonyl yields the corresponding alkyne-dicobalt hexacarbonyl, 6, which has been characterized by X-ray crystallography.