Electrophiles 17-ketenyl complex

Stepwise formation of hydroxy and alkoxy alkynes from carbonyl-car-byne coupling reactions has been studied by Kreissl and co-workers over the past decade (102). These coupling reactions typically form ketenyl complexes prior to electrophilic addition at oxygen to yield alkyne pro-... 

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... 

The nature of the postulated photo-generated intermediates 8, and the known reactivity of r 2-ketenyl ligands towards electrophiles suggested the possibility of trapping these intermediates with electrophilic reagents. Hence, the oxyacetylene derivatives 10 were obtained by irradiation of complexes 3 in the presence of HCl, acyl chlorides, and silyl chlorides (Eqs. 8 and 9). ... 

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. 

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