Fragmentation of a As4Ph4-chain on a tetranuclear cobalt cluster induced by thermolysis or by reaction with Fe-2(CO)(9)

Thermolysis of the tetranuclear cobalt cluster [Co-4(mu (3)-AsPh)(mu (4)-et a (2):eta (2):eta (1)-As4Ph4)(mu -CO)(2)(CO)(8)] (1) at 60 degreesC in benz ene for two days gives [Co-4(mu (3)-AsPh)(2)(mu (3)-eta (2):eta (1)-As2Ph2) (mu -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 Bs,Ph, chain occurs on treatment of 1 with [Fe-2(CO)(9)] in benzene at room temper ature for 3 days affording [Co-4(mu (3)-AsPh)(2){(mu (3)-eta (2):eta (1)-As 2Ph2)Fe(CO)(4)}(mu -CO)(CO)(9)] (3), in which one arsine atom of the As2Ph2 bridging ligand is additionally bound to an Fe(CO)(4) unit. Conversely rea ction of 1 with excess P(OMe)(3) at room temperature in benzene for a days gives the trisubstituted trimethylphosphite derivative [Co-4(mu (3)-AsPh)(m u (4)-eta (2):eta (2):eta (1)-As4Ph4)(mu -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 fo r the formation of the new complexes are proposed and discussed. (C) 2001 E lsevier Science B.V. All rights reserved.