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

The heterobimetallic complexes [MoW(mu-R(1)CCR(2)) (CO)(4)(eta-C5H5)(2)] (R(1) = H, R(2) = Ph 1a, Me 1b or H 1c; R(1) = R(2) = CO(2)Me 1d or Me 1e) have been isolated from the reaction of a mixture of [Mo-2(Co)(6)(eta-C5H5)(2)] and [W-2(CO)(6)(eta-C5H5)(2)] with the corresponding alkyne R(1)C=CR(2) in diglyme (2.5,8-trioxanonane). Thermolysis of complexes 1a-1d with pPh(2)Cl 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 R(1) and R(2), to give the products [MoW(mu-Cl) (mu-Ph(2)PCR(1)=CR(2)) (CO)(2)(eta-C5H5)(2)] (R(1) = H, R(2) = Ph 2a; R(1) = R(2) = H 2c or CO(2)Me 2d), [WMoCl2(mu-Ph(2)PC=CHR(2)) (mu-PPh(2))-(eta-C5H5)(2)] (R(2) = Ph 3a, Me 3b or H 3c), [MoWCl2(mu-Ph(2)PC=CHR(2))(mu-PPh(2))(eta-C5H5)(2)] (R(2) = ph 4a or Me 4b) and [WMo(mu-Cl){mu-Ph(2)PC(CO(2)Me)=CCO(2)Me}(CO)(2)(eta-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 df 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 1a via its reaction with PPh(3) gave [WMo(O)(mu-CH=CHPh)(mu-PPh(2))(CO) (eta-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 alpha carbon of the four-membered metallacycle are sigma bonded to tungsten and the carbon-carbon double bond is pi-coordinated to molybdenum.