Carbenes ketenyl

At the HF/6-31G level, ketenyl carbenes (1) were calculated to be intermediates in the decarbonylation of 1,2-bisketenes (2) to form cyclopropenones." At the MP2/6-31G and B3LYP levels, however, decarbonylation was predicted to form the cyclopropenones directly. The anfi-ketenyl carbenes were found to be 2.2-5.4kcalmoP higher in energy than the syn isomers (1). The mechanism of reaction of [l.l.ljpropellane with singlet dihalocarbene has been reported. ... 

Ketenyl carbenes are proposed as the key intermediates in the photochemical decomposition of maleic and dichloromaleic anhydrides in cryogenic matrices. The former anhydride yields cyclopropenone and ethyne while the latter yields dichlorocyclopropenone and dichloroethyne. Dichloropropadienone is observed as a minor product. Maleimide (155) is excited into its triplet state on irradiation in solvents. In hydrogen-donating solvents the radical (156) is... 

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. ... 

ABSTRACT. Dicarbonyl(t 5-cyclopentadienyl)carbyne complexes of molybdenum and tungsten prove to be a valuable synthetic tool Reaction with phosphines provides substituted carbyne complexes and leads via an intramolecular CC-coupling to t 1- or Tj -ketenyl complexes respectively. Electrophiles attack the metal carbyne triple bond forming hetero- and acyclic carbene complexes, r 2-acyl compounds, T -ketene complexes and metalla-dithia-bicyclobutane cations. Dithio-carboxylates are formed in reaction of these dicarbonyl(Ti5 cyclo-pentadienyl)carbyne complexes with sulfur or cyclohexene sulfide. 

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... 

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