Some Chemistry of Vinylidene Complexes

The majority of the chemistry of vinylidene and propadienylidene complexes is concerned with their synthesis and reactions, which have been 

Although no simple vinylidene complex was obtained from reactions between Cr(CO)5(OEt2) and methyl propiolate, complexes 60, 61, and 62 were formed in the ratio 4 5 1 (22) the latter two each contain two molecules of the alkyne, and may be formed from an intermediate Cr[=C=CH(C02Me)](C0)5 complex (22). 

In nonpolar solvents, 62 changes from red to violet, suggesting formation of the tautomer 62b  

A low yield of Cr[=C=C(COMe)CMe2(OCOMe)](CO)5 was obtained from the reaction of [Cr(C=CMe20)(C0)5]2 with acetyl chloride in the presence of triphenylphosphine (28). 

This is further indicated in the reactions of 3-butyn-l-ol with [Fe( /2-CH2=CMe2)(CO)2( -C5H5)]+, which afford a mixture of dihydrofuran complex (64) and the oxacyclopentylidene complex (65) (84). The formation of these two derivatives involves a common tp-alkyne intermediate, which either forms 64 directly by internal nucleophilic attack of the oxygen on the complexed C=C triple bond, or rearranges to the vinylidene. This forms 65 by a similar attack of the hydroxy group on the a-carbon, followed 

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