Pentacarbonylchromium dianion

In situ preparation of the vinylidene pentacarbonylchromium complexes was also reported by Fischer et al. [7]. Treatment ofthe acylchromate complexes 18, prepared by acylation of pentacarbonylchromium dianion, with trifiuoroacetic anhydride in the presence of DBU afforded very labile pentacarbonylchromium vinylidene complexes 19, which were, without isolation, reacted with several electron-rich alkynes such as ynamines, alkynyl ethers, and alkynyl thioethers to give the corresponding cyclobutenylidene chromium complexes in reasonable yield [8] (Scheme 5.5). 

Hydridocarbenes 8.19 are not available by this route. They can be prepared from formamides by reaction with the highly nucleophilic pentacarbonylchromium dianion 8.15, itself prepared by reduction of chromium hexacarbonyl with potassium/graphite (Scheme 8.4). The oxygen atom of the adduct 8.16 is removed using two equivalents of trimethylsilyl chloride. 

---

See also in sourсe #XX -- [ ]

---