The potential of a cyclo-As5 ligand complex in coordination chemistry

Abstract

The reaction of [Cp*Fe(η5-As5)] (1) with CuI halides leads to the formation of the 1D-polymeric compounds [{Cu(μ-X)}3(CH3CN){Cp*Fe(η5:η2:η2:η2-As5)}]n (X = Cl (2), Br (3)), [{Cu(μ3-I)}2{Cp*Fe(η5:η2:η2-As5)}]n (4) and [{Cu(μ-I)}3{CuI}{Cp*Fe(η5:η2:η2:η1:η1-As5)}{Cp*Fe(η5:η5:η2-As5)}]n (5). The polymers are built up by the π-coordination of the cyclo-As5 ring to (CuX)n moieties forming discrete units, which are additionally linked by weak intermolecular As⋯Cu σ-interactions. Only polymer 4 is an exception revealing a (CuI)n ladder which is alternately coordinated by molecules of 1. In a side arm of polymer 5 a novel η5-coordination of a Cu atom below the cyclo-As5 ring is found, showing an unprecedented heteroleptic triple-decker sandwich complex with a polyarsenic middle-deck. All products are characterised by single crystal X-ray structure analysis. To define the differences in the coordination behaviour of 1 and its phosphorus analogue [Cp*Fe(η5-P5)] (1a), DFT calculations are described.