Alkyne-phosphinoalkyne coupling reactions on mixed-metal tungsten-cobalt centres; P-C(alkyne) bond cleavage versus P-C(alkyne) bond preservation

Reactions of the alkyne-bridged tungsten-cobalt complexes [(eta (5)-C5H5)(O C)(2)W(mu -(RCCR2)-C-1)Co(CO)(3)] (R-1=R-2=CO2Me 1a; R-1=H, R-2=Bu-t 1b) wi th Ph2PC=CPh in refluxing toluene result in two different reaction pathways . On reaction with 1a three products are isolated namely, [(eta (5)-C5H5)(O C)(2)W{mu -C-2(CO2Me)(2)}Co(CO)(3)(PPh2C=CPh)] 2, the result of substitutio n of a cobalt carbonyl ligand by a phosphorus-bound molecule of Ph2PC=CPh, [(eta (5)-C5H5)(OC)(2)W{mu -PhCCC(CO2Me)=C(CO2Me)PPh2}Co(CO)(2)] 3 and [(et a (5)-C5H5)(OC)W{mu -C(CO2Me)=C(C=CPh)C(OMe)O}(mu -PPh2)Co(CO)(2)] 4, in wh ich phosphorus-carbon(alkyne) bond cleavage of the phosphinoalkyne has ocur red along with phosphorus-carbon bond formation (3) and/or carbon-carbon bo nd formation (3 and 4). In contrast, reaction of 1b with Ph2PC=CPh affords two products, [(eta (5)-C5H5)(OC)W{mu -(CBuCHCPhC)-C-t(PPh2)}Co(CO)(2)] 5 a nd [(eta (5)-C5H5)(OC)(2)W{mu -(CBuCHC)-C-t(PPh2)CPh}Co(CO)(2)] 6, in which the bridging alkyne has coupled with an intact molecule of the phosphinoal kyne Ph2PCalpha=CbetaPh at either its beta- or alpha -carbon atoms, respect ively. However, on reaction of 1b with the tert-butyl-substituted phosphino alkyne, Ph2PC=CBut, regiospecific coupling and oxidation of the phosphino m oiety occur to give [(eta (5)-C5H5)(OC)W{mu -CBut=CHCBut=C(PPh2O)}Co(CO)(2) ] 8, as the sole product. The reactivity of 6 towards diiron nonacarbonyl h as been explored and found to afford the trimetallic complex [(eta (5)-C5H5 )(OC)(2)W{mu -(CBuCHC)-C-t(PPh2Fe(CO)(4))CPh}Co(CO)(2)] 7 in good yield. Si ngle crystal X-ray diffraction studies have been performed on 4, 6, 7 and 8 and possible reaction pathways for the formation of the new complexes are proposed and discussed.