Carbonyl-carbyne coupling

The product ratio of substitution at the carbyne carbon vs. carbonyl-carbyne coupling can be tuned by variation of the aryloxide / 2ra-substituent, which... 

The first well established and characterized example of such a carbonyl-carbyne coupling reaction... 

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. 

The direct conversion of carbyne complexes TpW( = CR)(CO)2 (R = Ph, C6H4Me-4) to cationic c/ -dicarbonyl -phosphinocarbene (metallaphosphacyclo-propene) complexes can be achieved by the addition of chlorodiorganophosphines in the presence of sodium tetraphenylborate or thallium hexafluorophosphate (Scheme 51)/ In the absence of these sodium salts, nucleophile (Cl )-induced carbonyl-carbene coupling affords neutral -phosphinoketene complexes. 

Figure 5.42 Ketenyl formation via carbyne-carbonyl coupling Wl 2 = W(CO)Cp...

The c /.s-bis(phosphine)-substituted complexes 68 were found in our laboratory to isomerize to the trans derivatives under irradiation with visible light [Eq. (57)] (97). The isomerization reaction was postulated to involve a stereochemically nonrigid pentacoordinate intermediate which is generated by photochemical carbyne-carbonyl coupling. (The evidence for the ligand coupling step as well as other photoinduced coupling reactions are discussed in Section IV,F.)... 

Reaction of the tungsten complex 167 with diphenylphosphine at elevated temperatures affords complex 168 [Eq. (140)] (76i). The same compound could be obtained by sequential addition of LiPPh2 and NH4Br. Formation of this product is surprising considering the ease with which some phospines induce carbyne-carbonyl coupling in complex 167 (see Section IV,F). The by-product 169 could possibly be derived from an intermediate ketenyl complex. Protonation of complex 168 in acetonitrile occurs at the former carbyne carbon to give the phosphine complex 170. 

Hillhouse and co-workers discovered a new route to carbyne complexes which is based on the reverse of carbyne-carbonyl coupling (J72). Reaction of complex 200 with carbon suboxide affords the ketenyl complex 201 [Eq. (159)]. Formation of the ketenyl ligand in 201 was postulated to arise from attack of phosphine on an intermediate ketenylidene complex. Warming of complex 201 results in cleavage of the ketenyl ligand and formation of the phosphonium carbyne complex 202. This mechanism was put to work in a more direct fashion by reaction of complex 200 with PhjPCCO [Eq.(160)]. 

Nucleophiles react with carbyne complexes to promote (or trap) carbyne-carbonyl coupling products, attack the metal-carbon triple bond, or displace a substituent on the carbyne carbon. Complexes of the form Tp M( = CR)(CO)2 are coordinatively saturated and in the case of Tp = Tp, the metal also enjoys a substantial degree of steric protection. Accordingly, the reaction of these complexes with nucleophiles does not, in general, involve attack at the metal but rather at a coligand. Attempted synthesis of Tp W( = CMe)(CO)2 via reaction of MeLi with the... 

It has been proposed that these carbyne-acyl rearrangements start with the protonation of the car-byne carbon atom to initially give a carbene complex. For the next step two different pathways have been proposed i) An intramolecular carbene carbonyl coupling to yield a 7C-ketene complex,... 

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