Transformations of organoarsine-oxides and -sulfides on di- and tri-cobalt carbonyl centres

Conversion of [Co3(μ3-CR′){μ-(AsMe2)2O}(CO)7] [R′=Cl, Me] and [Co2{μ-C2(CO2Me)2}{μ-(AsMe2)2O}(CO)4] to the corresponding bis-dimethylarsinesulfide-bridged complexes [Co3(μ3-CR′){μ-(AsMe2)2S}(CO)7] [R′=Cl (1a), Me (1b)] and [Co2{μ-C2(CO2Me)2}{μ-(AsMe2)2S}(CO)4] (2) can be achieved on their treatment with H2S (with the elimination of H2O); this process is reversible. The related bis-diphenylarsinesulfide-bridged complexes, [Co3(μ3-CR′){μ-(AsPh2)2S}(CO)7] [R′=Cl (3a), Me (3b)] and [Co2(R′CCR′′){μ-(AsPh2)2S}(CO)4] [R′=R′′=CO2Me (4a), Ph (4b)] can be obtained in moderate yield by the direct reaction of (Ph2As)2S with [Co3(μ3-CR′)(CO)9] [R′=Cl, Me] and [Co2(R′CCR′′)(CO)6] [R′=R′′=CO2Me, Ph], respectively. The triphenylarsine mono-substituted complex [Co2{μ-C2(CO2Me)2}(CO)5(AsPh3)] (5) is also isolated as a product in the reaction leading to 4a. Thermolysis of 3a yields [Co3(μ3-S){μ-(AsPh2)2O}{μ-(AsPh2S)}(CO)7] (6) in low yield while the related thioxo-capped complexes [Co3(μ3-S){μ-(AsMe2)2X}(μ-AsMe2S)(CO)5] [X=S (7), O (8)] can be obtained in higher yield by thermolysis of [Co3(μ-CMe){μ-(AsMe2)2O}(CO)7] in the presence of H2S. Single crystal X-ray diffraction studies have been performed on 2, 4a, 4b and 8.