THE INFLUENCE OF THE RING SUBSTITUENT, R, ON THE SUBSTITUTION OF CARBONYL GROUPS BY PHOSPHINE-LIGANDS IN [CO2(MU-PPH2CHCRC(O))(MU-PPH2)(CO)4] (R = H, PH OR SIME3)

The room-temperature reaction of the complexes [Co2{mu-PPh 2CHCRC(O)}(mu-PPh2)(CO)4] (R = H 1a, Ph 1b or SiMe3 1c) with 1 equivalent of PPhMe2 gave a combination of phosphine substituted products which depends on the nature of R. When R = H 1 a, two isomeric monosubstituted complexes of formula [Co2{mu-PPh2CHCHC(O)}(mu-PPh2)(CO)3(PPhMe2)] 2a and 3a are afforded in a ratio of approximately 1 : 1 in which the phosphine co-ordinates either at the cobalt atom pi-co-ordinated by the carbon-carbon double bond (2a) or at the cobalt to which the PPh2 and CO groups of the metallacyclic ligand are sigma bonded (3a). When R = Ph lb, the corresponding monosubstituted derivatives, [Co2{mu-PPh2CHCPhC(O)}(mu-PPh2)(CO)3(PPhMe2)] 2b and 3b are formed together with traces of the disubstituted complex [Co2{mu-PPh2CHCPhC(O)}(mu-PPh2)(CO)2(PPhMe2)2] 4b. In the case of R = SiMe, 1c, only the monosubstituted isomer [Co2{mu-PPh2CHC(SiMe3)C(O)}(mu-PPh2)(CO)3(PPhMe2)] 3c is obtained. Conversion of the monosubstituted complexes 2a, 2b and 3a, 3b to the disubstituted complexes [Co2{mu-PPh2CHCRC(O)}(mu-PPh2)(CO)2(PPhMe2)2] (R = H 4a or Ph 4b) takes place on thermal reaction of respectively 2a, 3a and 2b, 3b with a further equivalent of PPhMe2. An X-ray crystal structural determination has been performed on complex 4a and reveals a pseudo-axial/cis arrangement of the phosphine groups which are located one on each cobalt atom. The complex [Co2{mu-PPh2CHCPhC(O)}(mu-PPh2)(CO)4] lb reacted with the secondary phosphine PPh2H initially in the same way as with PPhMe2 to give isomeric species of formula [Co2{mu-PPh2CHCPhC(O)}(mu-PPH2)(CO)3(PPh2H)] 2d and 3d. Thermolysis of complex 2d resulted in 42% conversion to the isomeric 3d along with traces of 1b band [Co2{mu-PPh2CHCPhC(O)}(mu-PPh2)(CO)2(PPh2H)2] 4d.