Cyclopropenylidene complex

In contrast to other terminal alkynes, the lithiated dimethylaminoethyne 40 does not give the corresponding alkynylcarbene but the cyclopropenylidene complex 41 (Scheme 7) [51]. Further addition of dimethylamine to 41 affords the substitution product 42 in excellent yield. This 2,3-bis(dimethylamino-cyclopropenylidene)pentacarbonylchromium (42) is extremely stable, and it cannot be transformed to the corresponding carbonyl compound, 2,3-bis... 

Scheme 2 shows the preparation of carbene complexes starting from [L M-ER3]" = [MeCp(CO)2Mn-SiMePlt2] and [(7r-arene)(CO)2Cr-SnPh3] [12,13]. By a related approach, a cationic cyclopropenylidene complex was prepared by reaction of Cp(CO)2FeSiMe3 with l-chloro-2,3-diphenylcyclopropenylium tetrafluoroborate [14],... 

C. Cyclopropenylidene Complexes of Divalent Germanium, Tin, and Lead Amides... 

Scheme 7. Cyclopropenylidene complexes of divalent germanium, tin, and lead.

Interaction of metals with cyclopropenylidene to form stable complexes has been widely studied340 in the last two decades since the first reported synthesis of pentacarbonyl(2,3-diphenylcyclopropenylidene)chromium (see belowy4. Two groups of cyclopropenylidene metal derivatives may be distinguished neutral cyclopropenylidene complexes represented by two resonance forms, and the cationic cyclopropenylium transition metal complexes of groups 6 (Cr, Mo, W), 7 (Mn), 8 (Fe) and 10 (Pd, Pt), whereas the latter cationic cr-complexes are derived from both main group metals (Li, Mg) and group 10 (Pd, Pt) transition metals. 

Thus, for group 10 palladium and platinum metals, a mixture of 1,2-bis(dialkylamino)-3-halocyclopropenylium halide and a slight excess of Pd or Pt black is refluxed in MeCN for 24h, affording the corresponding dimeric cyclopropenylidene //-complexes [(R2N)2C3 MX2 2 (R = Me, Et, i-Pr, M = Pd, Pt X = Cl, I) (equation 276)340 347-352. The dimers further react with Bu3P to give the planar mononuclear complex cis-[(R2N)2C3]MX2(PBu3). 

Use of chlorocyclopropenylium cations for the synthesis of neutral cyclopropenylidene complexes of transition metals other than group 10 is limited. One exceptional example is... 

TABLE 6. 13C NMR spectra of palladium cyclopropenylidene complexes [Cl2Pd(C3R2)]2 and cu-Cl2(Bu3P)Pd(C3R2), and cyclopropenylium salts [tranj-Cl(Bu3P)2Pd(C3R2)]C104... 

Nucleophilic carbenes have been reported to react with Eewis acidic group 14 complexes with the isolation of neutral or ionic compounds via simple adduct formation or displacement of a halide ion. > The range of carbene complexes of silicon, germanium, tin, and lead, as well as some related cyclopropenylidene complexes are described below. 

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