Synthesis of mono-, di- and tetra-alkyne functionalized calix[4]arenes: Reactions of these multipodal ligands with dicobalt octacarbonyl to give complexes which contain up to eight cobalt atoms

Abstract

The functionalized mono-alkynecone-monopropargyl p-tert-butylcalix[4]arene 1 was synthesized by the reaction of p-tert-butylcalix[4]arene with K₂CO₃ and 3-bromo-1-propyne. More prolonged reaction times led to the formation of the 1,3 cone bis(propargyl)calix[4]arene 2. The tetra-alkyne species cone-tetrapropargyl p-tert-butylcalix[4]arene 3 and its conformational isomer, 1,3-alternate-tetrapropargylcalix[4]arene 4 may both be prepared via related reaction sequences. The structures of the molecules 3 and 4 were both re-determined by single crystal X-ray diffraction studies. All four functionalized calixarenes react rapidly with dicobalt octacarbonyl to give [(calix[4]arene)·{Co₂(CO)₆}_n] species 5–9 (n = 1, 2 or 4) in which the alkyne functionalities of the propargylcalix[4]arenes are ligated to one or more [Co₂(CO)₆] groups. Two products could be harvested from the reaction of [Co₂(CO)₈] with the bis-propargyl-calixarene 2, depending on the reaction conditions and relative molar quantities of the reactants: complex 6, [1,3-cone bis(propargyl)calix[4]arene·{Co₂(CO)₆}₂], in which each alkyne group is bonded to a [Co₂(CO)₆] group, and complex 7, [1,3-cone bis(propargyl)calix[4]arene·{Co₂(CO)₆}], which contains a unligatedalkyne and an alkyne group bonded to a Co₂(CO)₆ unit. The structures of the tetracobalt and octacobalt complexes 6 and 8 were established by single crystal X-ray diffraction studies.