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

The new heterobimetallic complexes of general formula [{(R'S)Ph2P}(OC)(2)Co{mu-C-2(CO2Me)(2)}M(eta(5)-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-C=C or M-S-C=C (where M=Co, Mo or W), are accessible. While [{(PhS)Ph2P}(OC)(2)Co{mu-C-2(CO2Me)(2)}Mo(eta(5)-C5H5)(CO)(2)] 1a gives as the sole product the phosphorus-containing molybdenacyclic species [(OC)(eta(5)-C5H5)Mo{mu-PPh2C(CO2Me)C(CO2Me}(mu-SPh)Co(CO)(2)] 2a, the corresponding reaction of [{(R'S)Ph2P}(OC)(2)Co{mu-C-2(CO2Me)(2)}Mo(eta(5)-C5H5)(CO)(2)] (R'=Bu-n 1b; Bu-t 1c), results in the formation of both [(OC)(eta(5)-C5H5)Mo{mu-PPh2C(CO2Me)C(CO2Me)}(mu-SR')Co(CO)(2)] (R'=Bu-n 2b; Bu-t 2c) and [(OC)(2)Co{mu-SR'C(CO2Me)C(CO2Me)}(mu-PPh2)Mo(eta(5)-C5H5)(CO)] (R'=Bu-n 3b; Bu-t 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)(2)Co{mu-C-2(CO2Me)(2)}Mo(eta(5)-C5Me5)(CO)(2)] 1b gives three species, [(OC)(eta(5)-C5Me5)Mo{mu-PPh2C(CO2Me)C(CO2Me)}(mu-SPh)Co(CO)(2)] 2d and [(OC)(2)Co{mu-SPhC(CO2Me)C(CO2Me)}(mu-PPh2)Mo(eta(5)-C5Me5)(CO)] 3d, which are, respectively, analogues of 2a-3c and 3b, 3c, and in addition the phosphorus-containing cobaltacyclic species [(OC)(2)Co{mu-PPh2C(CO2Me)C(CO2Me)}(mu-SPh)Mo(eta(5)-C5Me5)(CO)] 4d. Thermolysis of [{((BuS)-S-n)Ph2P}(OC)(2)Co{mu-C-2(CO2Me)(2)}W(eta(5)-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)(2)Co{mu-(SBuC)-C-n(CO2Me)C(CO2Me)}(mu-PPh2)W(eta(5)-C5H5)(CO)] 3e or the tungsten centre as in [(OC)(eta(5)-C5H5)W{mu-(SBuC)-C-n(CO2Me)C(CO2Me)}(mu-PPh2)Co(CO)(2)] 5e. The 'flyover' complex [(OC)(eta(5)-C5H5)W{mu-C(CO2Me)CHC(OMe)O}(mu-SPh)Co(CO){PPh2(SPh)}] 6 was the only product obtained from the reaction of [(OC)(3)Co{mu-C-2(CO2Me)(2)}W(eta(5)-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.