Reactions of P2Ph4 with alkyne-bridged dicobalt carbonyl complexes; crystal structures of [Co2{µ-C2(CO2Me)2}(µ-P2Ph4)(CO)4], [Co2{µ-PPh2CHCPhC(O)}(µ-PPh2)(CO)4] and [Co2{µ-PPh2C(O)CHCH}(µ-PPh2)(CO)3(PPh3)]

Abstract

The reactions of P₂Ph₄ with a variety of substituted alkyne complexes [Co₂(µ-RCCR′)(CO)₆] in toluene give the complexes [Co₂(µ-RCCR′)(CO)₅(P₂Ph₄)]1(R = R′= CO₂Me 1a or Ph 1b; R = Ph, R′= H 1c and [Co₂(µ-RCCR′)(µ-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(µ-PPh₂CRCR′)(µ-PPh₂)(CO)₄]3(R = R′= CO₂Me 3a or Ph 3b and [Co₂{µ-PPh₂CRCR′C(O)}(µ-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 π-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(µ-HCCH)(CO)₆] reacts with P₂Ph₄ differently from the substituted derivatives to give as the principal product [Co₂{µ-PPh₂C(O)CHCH}(µ-PPh₂)(CO)₄]5b. The structure of the PPh₃ derivative of this complex, [Co₂{µ-PPh₂C(O)CHCH}(µ-PPh₂)(CO)₃(PPh₃)]6d, has been determined by X-ray diffraction.