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

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.