Carbyne-alkyne coupling reactions

A number of other C-C bond forming reactions have been described which afford not allenyl but metalloallyl clusters. Carbyne-alkyne coupling reactions are potentially useful as sources of allenyl fragments but... 

The application of the nucleophilic or electrophilic induced carbonyl carbyne coupling reaction has been perfectly demonstrated by E. O. Fischer [13,14], R. R. Schrock [15], J. L. Templeton [16,17], F. G. A. Stone [18], Angelici [19,20], A. Mayr [21,22], R. J. G. L. Geoffroy [23] and S. J. Lippard [24], preparing a variety of interesting ketenyl, alkyne and binuclear complexes involving r 2-ketenyl species as possible intermediates. 

Reactions A carbyne can couple with another carbyne to give an alkyne or alkyne complex.For instance, Br(CO)4Cr CPh reacts with Ce(IV) to give free PhC CPh. Carbynes also have extensive photochemistry. In the Fischer series, the carbyne carbon is electrophilic and subject to nucleophilic attack, for example, by PMcj, pyridine, RLi, or isonitrile (= Nu) to give a carbene of the type L M=CR(Nu). Alternatively, the nucleophile may attack the metal in L (CO)M=CR and produce a ketenyl complex... 

Oxidative coupling and reductive cleavage are yet two additional reaction types in which the names reflect metal-based redox changes.In this regard, the metal-catalyzed reactions of carbon monoxide with other donor molecules such as isonitriles (RNC), carbynes (CR), alkenes, and alkynes, often referred to in the literature as reductive couplings to reflect the transformations affecting the ligands, frequently involve metal-based oxidations and should... 

The photochemistry of metal carbyne complexes is in many ways similar to the photochemistry of metal carbene complexes, but the reactions have not been developed or become as synthetically useful as the photochemistry of metal carbene complexes. Among reported reactions are couplings with ancillary CO ligands to form ketenyl complexes, protonation of the carbyne carbon, insertions into C-H bonds, addition of the carbyne carbon to an alkyne to produce a cyclopropenyl complex, and electron-transfer reactions. ... 

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