REACTIONS OF P2PH4 WITH ALKYNE-BRIDGED DICOBALT CARBONYL-COMPLEXES - CRYSTAL-STRUCTURES OF [CO2(MU-C2(CO2ME)2)-(MU-P2PH4)(CO)4], [CO2(MU-PPH2CHCPHC(O))(MU-PPH2)(CO)4] AND [CO2(MU-PPH2CO(O)CHCH)(MU-PPH2)(CO)3(PPH3)]

The reactions of P2Ph4 with a variety of substituted alkyne complexes [Co2(mu-RC = CR')(CO)6] in toluene give the complexes [Co2(mu-RC = CR') (CO)5(P2Ph4)] 1 (R = R' = CO2Me 1a or Ph 1b; R = Ph, R' = H 1c and [Co2(mu-RC = CR')(mu-P2Ph4)(CO)4] 2 (R = R' = Ph 2b; R = Ph, R' = H 2c. All three derivatives of type 1 are cleanly converted into 2 on thermolysis. An X-ray diffraction study of 2a reveals a square-planar Co2P2 core with the symmetrical alkyne perpendicular to the Co-Co bond. Further thermolysis of complexes 2 produces [Co2(mu-PPh2CRCR')(mu-PPh2)(CO)4] 3 (R = R' = CO2Me3a or Ph 3b and [Co2{mu-PPh2CRCR'-C(O)}(mu-PPh2)(CO)4] 4c (R = H, R' = Ph). The structure of 4c has been determined by X-ray analysis. The PPh2CHCPhC(O) ligand forms a five-membered metallacyclic ring incorporating one Co atom and is pi-bonded to the other Co atom. Complexes 3a and 3b are partially converted into 4a (R = R' = CO2Me) and 4b (R = R' = Ph) on treatment with CO. This reaction is reversed by heating 4a and 4b in solution or, more slowly, on standing at room temperature. The parent acetylene complex [Co2(mu-HC = CH)(CO)6] reacts with P2Ph4 differently from the substituted derivatives to give as the principal product [Co2{mu-PPh2-C(O)CHCH}(mu-PPh2)(CO)4] 5d. The structure of the PPh3 derivative of this complex, [Co2{mu-PPh2-C(O)CHCH}(mu-PPh2)(CO)3(PPh3)] 6d, has been determined by X-ray diffraction.