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

Abstract

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(µ₄-AsPh)₂(CO)₁₀] 1 and [Co₄(µ₃-AsPh)(µ₄-η²∶η²∶η¹-As₄Ph₄)(CO)₁₀] 2. In contrast, reaction of cyclo-(PhAs)₆ with the alkyene-bridged complexes [Co₂(µ-R¹CCR²)(CO)₆] in toluene or in benzene at 65 °C afforded the new complexes [Co₂(µ-R¹CCR²){µ-cyclo-(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 pseudo-octahedral 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.