Ketenylidene ligand

The related iron carbonyl complex 55 was obtained by the reaction of [Fe3(CO)i2] with C(PPh3)(CO) however, according to [95] it is questionable because the spectroscopic data do not match with those of related compounds. The Mn and Re complexes [Cp(CO)2M C(PPh3)(CO) ] (M = Mn (56), Re (57)) have also been reported the ylide replaces the labile ether ligand in [Cp(CO)2M (OEt2)] [142]. The examples with the bonded ketenylidene ligand C(PPh3)(CO) are summarized in Fig. 30. 

Ketene and ketenylidene ligands bound to trimetaUic frameworks undergo very interesting chemistry. The transformations involving these ligands may have some relevance to the chemistry of carbon atoms on metal surfaces. 

The carbonyl of the ketenylidene ligand undergoes a very interesting substitution reaction with phosphine ligands. Initial... 

Reaction (7) proceeds at room temperature and at one atmosphere pressure of carbon dioxide, thus converting the bridging ketenylidene ligand into the bridging oxided The ketenylidene complex reacts with carbon dioxide even in the solid state the gas produced from the zirconium derivative, promptly evacuated into a mass-spectrometer, was shown to be carbon suboxide C302d The inorganic reaction product appears to catalyze the polymerization of carbon suboxide to red solid productsd The structure of the product resulting from reaction (7), R = Pr , is shown in Fig. 8b. 

Ketenes can react in several ways with organometallic compounds and complexes. They can add as ligands to coordinated metals forming stable ketene, ketenyl, and ketenylidene complexes. Ketenes can be inserted into metal-hydride, metal-alkyl, metal-OR, and metal-NR bonds, react with metal—oxide complexes, and with coordinated ligands. This chemistry has been reviewed (9,51). 

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)]. 

Wolczanski and co-workers have developed the chemistry of Nb and Ta centers supported by siloxo ligands.60 Addition of 2 eq Nafsilox) (silox = Bu SiO-) to TaCl2(CH2But)3 in C6H6 provided (silox)2Ta(=CHBut)(CH2But). 1 Treatment of (silox)3Tain ((32) Scheme 44) with CO produced (silox)3Ta=0 and binuclear [(silox)3Ta]2(/i2- 1 1-C2). Different reaction conditions also produced the ketenylidene complex (silox)3Ta=C=C=0 (Scheme 44).62,63 The mechanism of formation of these species was studied in detail. 

The reactien scheme in Fig. 2.50 shews an example ef hew a ketenylidene metal cemplex can be used as precurser fer a bridged carbide ligand that can be subsequently used fer preparing a variety ef new heterenuclear cemplexes. 

The trinuclear ketenylidene complex, [FCs(iJ,s-C=C=0)iCO)gf 76, serves as a versatile starting compound for (i) heteronuclear ketenylidene complexes, (jj) 3-alkylidyne complexes (via G=GO bond cleavage), and (iii) G2 complexes (via conversion into /X3-G=G-OX ligands), as described in GOMG(1995). Treatment of 76... 

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