Novel Approach to Intermediates Containing a Tungsten−Arsenic Triple Bond^†

Thermolysis of the arsenidene complex [Cp*As{W(CO)5}2] (1) gave [Cp*(CO)2W(η3-As3)] (2), [{W(CO)3Cp*W}2(μ3-As)4] (3), and [{W(CO)3Cp*W}2(μ3-As)3{μ3-AsW(CO)5}] (4). The products show that 1 has undergone a Cp* migration from the σ-bound state at the As atom to η5 coordination at the transition metal, presumably via an intermediate of the type [Cp*(CO)2W⋮As→W(CO)5]. In a second transformation pathway removal of the Cp* group of the arsenidene complex 1 occurs to form an unsaturated species of the type [As{W(CO)5}2]. Compound 2 exhibits the unusual formation of a cyclo-As3 ligand, while the tetrahedral tungsten clusters 3 and 4 represent possible tetramers of the intermediates formed in both pathways. Furthermore, photolysis of arsenidene complex 1 results in [As2{W(CO)5}3] (5), which shows that the second pathway prevails under these conditions.