Carbyne, reactive activity

The nature of the reactive intermediates involved in hydrocracking or in skeletal rearrangements of hydrocarbons is still under active discussion. Many arguments are in favour of metalla-carbyne or metalla-carbene like complexes . However, several experimental results may only be explained by proposing metalla-cyclobutanes or cr-alkyl-metal species as adsorbed reactive intermediates ", and they depend strongly on the nature of the active sites (e.g. large or small size particles, single crystal metal surfaces ). 

Alkyne metathesis, using either preformed carbyne complexes, or carbyne complexes generated in situ, has started to find use in recent years, particularly as more reactive catalysts have been developed. The introduction of stable carbyne complexes, such as tungsten complex 8.483, as more-active catalysts started to make the reaction practicable for organic synthesis. ... 

The preparation and study of metallacycles has been a subject of active investigation for organometallic chemists. We have just seen one example where metallacycle formation is a key step in a catalytic process and there are several others most notably, olefin metathesis. The metal acts as a geometrical and electronic template in these reactions. For unsaturated metallacycles there are interesting questions concerning delocalization [29]. Certain metal carbynes can react with acetylene to give metallacyclobutadienes as intermediates [30]. One such example of an insoluble molecule is the tungstenacyclobutadiene complex, 18.36 [31]. The compound is quite stable and not very reactive (in contrast to cyclobutadienes... 

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