Propadienylidene complexes reactions

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

The anionic complexes (50) are obtained from the group VI carbonyl and the dilithium derivatives of the hydroxyalkynes HC=CCR2(OH) subsequent protonation or acylation affords propadienylidene (51) or carbene (52) complexes by complex cyclization and addition reactions (Scheme 3) (28). Attempts to obtain the dimethyl complex by reaction of the chromium alkynolate dianion with COCl2 gave only polymeric material. More stable complexes were obtained with R = aryl (73). 

These reactions are analogous to those observed for the corresponding vinylidene complexes the second propadienylidene group is lost, presumably as R2C=(C=C)2=CR2 only in one instance has this hydrocarbon been detected in the thermal decomposition of a mononuclear complex (77). The tendency for the propadienylidene residue to bridge two metal atoms is so great that the binuclear complexes are often formed in reactions designed to generate the mononuclear derivatives (73). 

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