Ketenyl ligands

Addition of the electron-rich amino alkyne, Et2NC=CMe, to the 172-ketenyl tungsten complex, (T 2-RC=C=0)CpW(PMe3)(C0), results in trimethylphosphine substitution and opening of the Tj2-ketenyl ligand to an V-ketenyl [Eq. (18)] (71). 

Kreissl has pointed out that the rj -ketenyl ligand in CpW(CO)(Et2-NC=CMe)[i71-C(CO)C6H4Me] acts as a multiple electron donor with resonance form ii below an important contributor to the description of this ligand (71). The impact of this 7r-donor role for the V-ketenyl ligand on the cis-alkyne geometry is minimal as the aminoalkyne ligand structural parameters fall in the range typical of four-electron donor alkynes. 

Treatment of the molybdenum alkylidyne complex 191 with 300 atm CO affords a mixture of three products the products of substitution of one and two phosphite ligands and complex 192 [Eq. (154)] (91). The methox-ycarbonyl group in 192 may have arisen from the reaction of an intermediate ketenyl ligand with methanol (derived from hydrolysis of trimethyl-phosphite). Reaction of the compounds 193 with xylylisocyanide was shown to give complexes 194 [Eq. (155)] (91). The products contain the... 

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)]. 

The second cage again bears a BCH2R fragment, while the metal-metal bond is spanned by the n-a,r 2 ketenyl ligand. However, the already... 

Ynolate (or ketenyl) ligands RCCO in organometallic chemistry have become easily accessible by the coupling of alkylidyne and carbonyl ligands ". The first coupling of this type was reported in 1976 in the reaction of tungsten alkylidyne-carbonyl complex 31 with trimethylphosphine leading to ynolate complex 32 (equation 21) ... 

Strained 13-vertex cage system is apparently unable to adopt a hyper-closo configuration, and a third carbonyl ligand is retained to donate the required electron pair to the cluster. This necessitates a transfer of the ketenyl ligand such that in the solid state it becomes rr-bonded to the metal vertex of the cage bearing the BCHjR substituent and // -bonded to the metal vertex of the cage involved in the interaction. However, NMR... 

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 chloro(methyl)platinum complex with dppe as a ligand reacts with Ph3P=C=C=0 in the presence of AgBp4 to form the cationic complex with the ketenyl ligand, 144 (Scheme Addition of alcohol to the C=C double... 

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