Metal—carbon triple bonds oxidation reactions

Reactions of carbyne complexes that maintain the integrity of the metal-carbon triple bond form the third route to new carbynes. Substituent modification, ligand exchange, oxidation, and reduction reactions have all been reported (see, e.g., Ref. 126). 

The metal-carbon triple bond chemistry of ruthenium and osmium described in this article bears a close resemblance to the metal-carbon double bond chemistry of these elements as exemplified by the methylene complexes [26]. In both systems two structural classes are found, five coordinate (trigonal bipyramidal, formally zero oxidation state) and six coordinate (octahedral, formally +2 oxidation state). In both systems the five coordinate compounds exhibit multiple metal-carbon bonds which are rather non-polar and typically undergo addition reactions with electrophilic reagents. On the other hand the six coordinate compounds, both M=C and M=C, begin to show electrophilic character at the carbon centres especially in cationic complexes. Further development of the carbyne chemistry of ruthenium and osmium will depend upon the discovery of new synthetic methods allowing the preparation of a broader range of compounds with widely differing carbyne substituents. 

Table 1. The Reaction of Metal Triple Bonds Oxides and Alkoxides at Carbon-carbon Double and ...

Acetylenes can react with metal complexes in a number of ways. Internal acetylenes usually coordinate to metal centers in a q -fashion, in whieh the C=C triple bond donates electrons to the metal center, and both carbon atoms form metal-carbon bonds. Terminal acetylenes can also coordinate to metal centers in this fashion, but ean react in other ways as well. In particular, because the acetylenic hydrogen atom is relatively acidic for a hydrocarbon, the C—H bond of terminal acetylenes ean also add oxidatively to metal centers to form metal acetyhde complexes. In some cases, however, a third kind of reaction is seen, in which the terminal aeetylene rearranges to a vinylidene complex, M=C=CHR. 

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