Binucleating behaviour of a proximally-diphosphinated calix[4]arene

Abstract

The long diphosphine 5,11-diphenylphosphanyl-25,26-dipropyloxy-27,28-bis(2-propenyloxy) calix[4]arene (cone) (5), in which the two phosphorus atoms are separated by a semi-rigid linking unit, was prepared in four steps starting from calix[4]arene. Reaction of 5 with AuCl(SEt₂) or [RuCl₂(p-cymene)]₂ led to calixarenes bearing two metallated pendant arms, [5·(AuCl)₂] and [5·{RuCl₂(p-cymene)}₂], respectively. In the presence of AgBF₄ or [Ni(C₅H₅)(1,5-cyclooctadiene)]BF₄, diphosphine 5 displayed a marked tendency to form oligomeric material, but under high dilution conditions dimeric species were obtained selectively. The inability of 5 to form chelate complexes was further illustrated by its reaction with [PdCl₂(1,5-cyclooctadiene)₂], which led quantitatively to a rare complex in which a diphosphine spans across the dinuclear [PdCl(μ-Cl)₂PdCl] unit.