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

Abstract

The reaction of [Cp*Fe(η⁵-As₅)] (1) with Cu^I 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.