Pentamethylcyclopentaarsine displaces ethanol from M(CO)5EtOH (M = Cr, Mo, W) to yield dinuclear species [M(CO)5]2(AsMe)5 in which the cyclic arsine ring is still intact. Other displacement reactions involving the cyclic arsine and di- and tri-substituted metal carbonyl derivatives also gave compounds containing an intact arsine ring. Thermal reactions between M(CO)6 (M = Cr, Mo, W) and the arsine yield the compounds [M(CO)4(AsMe)5]2 which are bridged arsenido derivatives containing chains of arsenic atoms linking two metal atoms. The complexes [Mo(CO)3(AsEt)4]2 and [Mo(C0)4(AsEt)4]2 were both obtained in the reaction involving (AsEt)5 with Mo(CO)6.