Fragmentation of a As4Ph4-chain on a tetranuclear cobalt cluster induced by thermolysis or by reaction with Fe2(CO)9

Thermolysis of the tetranuclear cobalt cluster [Co4(μ3-AsPh)(μ4-η2:η2:η1-As4Ph4)(μ-CO)2(CO)8] (1) at 60°C in benzene for two days gives [Co4(μ3-AsPh)2(μ3-η2:η1-As2Ph2)(μ-CO)(CO)9] (2), in which the tetraarsine chain in 1 has been cleaved to give the bridging As2Ph2 unit in 2. Similar fragmentation of the As4Ph4 chain occurs on treatment of 1 with [Fe2(CO)9] in benzene at room temperature for 3 days affording [Co4(μ3-AsPh)2{(μ3-η2:η1-As2Ph2)Fe(CO)4}(μ-CO)(CO)9] (3), in which one arsine atom of the As2Ph2 bridging ligand is additionally bound to an Fe(CO)4 unit. Conversely, reaction of 1 with excess P(OMe)3 at room temperature in benzene for 3 days gives the trisubstituted trimethylphosphite derivative [Co4(μ3-AsPh)(μ4-η2:η2:η1-As4Ph4)(μ-CO)2(CO)5{P(OMe)3}3] (4), in which the As4Ph4 unit remains intact. Single crystal X-ray diffraction studies have been performed on 2, 3 and 4 and possible reaction pathways for the formation of the new complexes are proposed and discussed.