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

The calixarenes 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(diphenylphosphinomethoxy)calix[4]arene (L-1) 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(L-2), substituted at the lower rim, reacted with 4 equivalents of[AuCl(tht)] (tht = tetrahydrothiophene) to yield respectively the tetragold complexes [(AuCl)(4)L-1] 1 and [(AuCl)(4)L-2] 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 L-2 With 2 equivalents of [AuCl(tht)] resulted in the formation of a mixture of two compounds. One, [(AuCl)(2)L-2] 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) Angstrom], resulting in a loose polymeric structure in the solid state. Reaction of L-1 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 (Delta G(double dagger) = 79.4 kJ mol(-1)). The silver analogue 5 was obtained by treating L-1 with AgBF4.