Phosphorus–carbon bond formation in heterobimetallic molybdenum–tungsten alkyne complexes

Abstract

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.