(PhAs)(6) and ((BuAs)-Bu-t)(4) as synthons for complexes with an acylic As-3 and a (Bu7As9)-Bu-t ligand

The cothermolysis of [Cp " Ta(CO)(4)] (1) (Cp " = C5H3Bu2t-1,3) and (PhAs)( 6) (2) affords the trinuclear tantalum cluster [{Cp " Ta}(3)(mu-O)(2)(mu(3) -CPh) (As-3)] (3) the Ta3As3 core of which consists of three severely disto rted tetrahedra with two common faces. The reaction of (RAs)(4) (6) with [F e-2(CO)(9)] (7) at room temperature gives [(R7As9){Fe(CO)(4)}] (8), R = Bu- t. The novel R7As9 ligand forms two As four-membered rings connected by an AsR bridge.