PHOSPHORUS-CARBON BOND FORMATION IN HETEROBIMETALLIC MOLYBDENUM-TUNGSTEN ALKYNE COMPLEXES

The heterobimetallic complexes [MoW(µ-R1CCR2)(CO)4(η-C5H5)2](R1= H, R2= Ph 1a, Me 1b or H 1c; R1= R2= CO2Me 1d or Me 1e) have been isolated from the reaction of a mixture of [Mo2(CO)6(η-C5H5)2] and [W2(CO)6(η-C5H5)2] with the corresponding alkyne R1CCR2 in diglyme (2,5,8-trioxanonane). Thermolysis of complexes 1a–1d with PPh2Cl proceeded via P–Cl bond cleavage and coupling of the diphenylphosphide unit with the alkyne in one of four different ways, depending on the nature of R1 and R2, to give the products [MoW(µ-Cl)(µ-Ph2PCR1CR2)(CO2)(η-C5H5)2](R1= H, R2= Ph 2a; R1= R2= H 2c or CO2Me 2d), [WMoCl2(µ-Ph2PCCHR2)(µ-PPh2)(η-C5H5)2](R2= Ph 3a, Me 3b or H 3c), [MoWCl2(µ-Ph2PCCHR2)(µ-PPh2)(η-C5H5)2](R2= Ph 4a or Me 4b) and [WMo(µ-Cl){µ-Ph2PC(CO2Me)CCO2Me}(CO)2(η-C5H5)2]5d. The formation of complexes 2 and 3 can be rationalised as resulting from initial substitution of a molybdenum carbonyl ligand by the halogenophosphine and that of 4 and 5 by initial substitution of a tungsten carbonyl. The significantly higher yield of the former two complexes suggests that initial substitution of a molybdenum carbonyl is the preferred pathway. Attempts at the preparation of an organophosphine-substituted derivative of 1avia its reaction with PPh3 gave [WMo(O)(µ-CHCHPh)(µ-PPh2)(CO)(η-C5H5)2]6 as the only product. A single-crystal X-ray structure determination of complex 3a shows a Mo–W distance compatible with a double bond. The phosphorus atom and the α carbon of the four-membered metallacycle are σ bonded to tungsten and the carbon–carbon double bond is π-co-ordinated to molybdenum.