NEW ORGANOARSINO-BRIDGED COBALT CARBONYL-COMPLEXES DERIVED FROM REACTIONS OF [CO-2(CO)(8)] OR [CO-2(MU-ALKYNE)(CO)(6)] WITH CYCLO-(ASPH)(6)

Reaction of hexaphenylcyclohexaarsane (PhAs)(6) with [Co2(CO)(8)] in t oluene at ambient temperature resulted in As-As bond cleavage and the new complexes [Co-4(mu(4)-AsPh)(2)(CO)(10)] 1 and AsPh)(mu(4)-eta(2):e ta(2):eta(1)-As4Ph4)-(CO)(10)] 2. In contrast, reaction of cyclo-(PhAs )(6) with the alkyene-bridged complexes [Co-2(mu-(RC)-C-1=CR2)(CO)(6)] in toluene or in benzene at 65 degrees C afforded the new complexes [ Co-2(mu-(RC)-C-1=CR2){mu-cyclo-(PhAs)(6)}(CO)(4)] (R-1 = R-2 = H 3; or Ph 4 and 5 (isomers); R-1 = Ph, R-2 = H 6; R-1 = Me, R-2 = H 7) in wh ich the As-6 ring remains intact. All seven products have been charact erised spectroscopically and, in addition, compounds 1-4 have been str ucturally characterised by X-ray diffraction analysis. The molecular s tructure of I comprises a rectangle of cobalt atoms capped above and b elow the plane by two quadruply bridging AsPh ligands, giving a pseudo octahedral Co4As2 core. The molecular structure of 2 consists of two d iscrete Co-2(CO)(5) units linked by an As4Ph4 chain and an AsPh unit. In complexes 3-7 the six-membered As-6 ring remains intact and acts as a bidentate bridging ligand replacing two equatorial carbonyl groups, one on each Co atom.