New organoarsino-bridged cobalt carbonyl complexes derived from reactions of [Co₂(CO)₈] or [Co₂(n-alkyne)(CO)6] with cych-(AsPh)6

Reaction of hexaphenylcyclohexaarsane (PhAs)6 with [Co₂(CO)8] in toluene at ambient temperature resulted in As-As bond cleavage and the new complexes [Co4(u4-AsPh)2(CO)IO] 1 and [Co4(uj-AsPh)(u4-T|2:r|2:r|'-As4Ph4)(CO)10] 2. In contrast, reaction of c>r/o-(PhAs)6 with the alkyene-bridged complexes [Co2(u-R'C=CR2)(CO)6] in toluene or in benzene at 65 °C afforded the new complexes [Co2(u-R'GCR2){u-c>'c/0-(PhAs)6}(CO)4] (R1 = R2 = H 3; or Ph 4 and 5 (isomers); R1 = Ph, R2 = H 6; R1 = Me, R2 = H 7) in which the As6 ring remains intact. All seven products have been characterised spectroscopically and, in addition, compounds 1-4 have been structurally characterised by X-ray diffraction analysis. The molecular structure of 1 comprises a rectangle of cobalt atoms capped above and below the plane by two quadruply bridging AsPh ligands, giving a pseudooctahedral Co4As2 core. The molecular structure of 2 consists of two discrete Co2(CO)5 units linked by an As4Ph4 chain and an AsPh unit. In complexes 3-7 the six-membered As6 ring remains intact and acts as a bidentate bridging ligand replacing two equatorial carbonyl groups, one on each Co atom.