Cumulene --complexes

A detailed computational study of the bonding in the zirconocene cyclopentyne complex suggests that the metallacyclopentyne depiction does not adequately describe the electronic structure of the complexes.152 The structure is best represented as a hybrid intermediate between the cumulene complex and the metallacyclopentyne... 

Dehydration of propargyl alcohols occurs commonly on mononuclear ruthenium complexes.[ l Water is formed from the terminal alkynic hydrogen and by the alcoholic OH this is the more common dehydration process (it is denoted Route A). These reactions afford organic intermediates leading to cumulene complexes useful for the synthesis of doped polyacetylenes or of non-linear optic materials. Dehydration of rhodium-coordinated propargyl alcohols " leads to free or coordinated cumulenes and can be catalyzed by alumina and chloride ions, Fig. 16. 

Also, bi- and trimetallic cumulene complexes, such as M=C=M, M=M=C, M=M=M and M=C=C=M are known. Cationic ruthenium allenylidene complexes are used as catalysts for ring closing metathesis reactions. Nonlinear optical properties have been measured for the Group 6 cumulenylidene complexes. Also, cationic chromium or iron vinylidene complexes undergo [2-1-2] cycloaddition reactions across imines to give fi-lactams. This reaction is useful for the synthesis of j8-lactam antibiotics. ... 

The metal cumulene complex 9 reacts with diazomethane and carbon monoxide to give 1,1-disubstituted butatrienes 10. ... 

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