Mobility of gold and silver ions around a macrocyclic polyphosphane. Supramolecular architecture of a digold–calix[4]arene complex

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Abstract
The calixarenes 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(diphenylphosphinomethoxy)calix[4]arene (L1) and 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(1,3,5-trimethyl-4,6-dioxo-1,3,5-triaza-2-phosphorinan-2-yl)calix[4]arene (L2), substituted at the lower rim, reacted with 4 equivalents of [AuCl(tht)] (tht = tetrahydrothiophene) to yield respectively the tetragold complexes [(AuCl)4L1] 1 and [(AuCl)4L2] 2, both adopting a cone conformation. The solid state structure of 1 has been determined by an X-ray diffraction study, which reveals crystallographic twofold symmetry. The reaction of L2 with 2 equivalents of [AuCl(tht)] resulted in the formation of a mixture of two compounds. One, [(AuCl)2L2] 3, could be isolated and was characterised by an X-ray diffraction study. The gold atoms of 3 are tethered to two distal P atoms. Intermolecular Au · · · Au contacts are observed for each gold atom [3.2879(7) Å], resulting in a loose polymeric structure in the solid state. Reaction of L1 with [AuCl(tht)] and TlPF6 resulted in quantitative formation of the dinuclear complex [Au2L1][PF6]2 4 where each gold atom is chelated by two proximal phosphino groups. Fast rotation of the gold atoms around the axis of the calixarene occurs in solution. In this co-operative intramolecular movement each gold atom switches from one pair of P atoms to an adjacent one (ΔG ‡ = 79.4 kJ mol–1). The silver analogue 5 was obtained by treating L1 with AgBF4.

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