The formation and transformation of metallacycles containing phosphorus or sulfur on molybdenum– or tungsten–cobalt mixed-metal backbones ‡

Abstract

The new heterobimetallic complexes of general formula [{(R′S)Ph2P}(OC)2Co{µ-C2(CO2Me)2}M(η5-L)(CO)2] 1 [L = C5H5 or C5Me5; M = Mo or W; R′ = hydrocarbyl] undergo thermally induced phosphorus–sulfur bond breaking reactions. By variation of the nature of the R′ substituent, the cyclopentadienyl group or the Group 6 metal centre in 1, bimetallic complexes incorporating bridging four-membered metallacycles of the type M–P–CC or M–S–CC (where M = Co, Mo or W), are accessible. While [{(PhS)Ph2P}(OC)2Co{µ-C2(CO2Me)2}Mo(η5-C5H5)(CO)2] 1a gives as the sole product the phosphorus-containing molybdenacyclic species [(OC)(η5-C5H5)Mo{µ-PPh2C(CO2Me)C(CO2Me}(µ-SPh)Co(CO)2] 2a, the corresponding reaction of [{(R′S)Ph2P}(OC)2Co{µ-C2(CO2Me)2}Mo(η5-C5H5)(CO)2] (R′ = Bun 1b; But 1c), results in the formation of both [(OC)(η5-C5H5)Mo{µ-PPh2C(CO2Me)C(CO2Me)}(µ-SR′)Co(CO)2] (R′ = Bun 2b; But 2c) and [(OC)2Co{µ-SR′C(CO2Me)C(CO2Me)}(µ-PPh2)Mo(η5-C5H5)(CO)] (R′ = Bun 3b; But 3c). The latter sulfur-containing cobaltacyclic species (3c) has been shown to isomerise to the phosphorus-containing molybdenacyclic species 2c on further heating. Conversely, employment of the pentamethylcyclopentadienyl complex [{(PhS)Ph2P}(OC)2Co{µ-C2(CO2Me)2}Mo(η5-C5Me5)(CO)2] 1b gives three species, [(OC)(η5-C5Me5)Mo{µ-PPh2C(CO2Me)C(CO2Me)}(µ-SPh)Co(CO)2] 2d and [(OC)2Co{µ-SPhC(CO2Me)C(CO2Me)}(µ-PPh2)Mo(η5-C5Me5)(CO)] 3d, which are, respectively, analogues of 2a–3c and 3b, 3c, and in addition the phosphorus-containing cobaltacyclic species [(OC)2Co{µ-PPh2C(CO2Me)C(CO2Me)}(µ-SPh)Mo(η5-C5Me5)(CO)] 4d. Thermolysis of [{(BunS)Ph2P}(OC)2Co{µ-C2(CO2Me)2}W(η5-C5H5)(CO)2] 1e, in which a tungsten centre has been introduced in place of the molybdenum in 1b, affords only sulfur-containing metallacyclic products, which incorporate either the cobalt centre as in [(OC)2Co{µ-SBunC(CO2Me)C(CO2Me)}(µ-PPh2)W(η5-C5H5)(CO)] 3e or the tungsten centre as in [(OC)(η5-C5H5)W{µ-SBunC(CO2Me)C(CO2Me)}(µ-PPh2)Co(CO)2] 5e. The ‘flyover’ complex [(OC)(η5-C5H5)W{µ-C(CO2Me)CHC(OMe)O}(µ-SPh)Co(CO){PPh2(SPh)}] 6 was the only product obtained from the reaction of [(OC)3Co{µ-C2(CO2Me)2}W(η5-C5H5)(CO)2] with Ph2P(SPh). Single crystal X-ray diffraction studies have been performed on complexes 1d, 2b, 3c′ [the P(OMe)3-substituted derivative of 3c], 5e and 6.