Alkyne-bridged dicopper(I) complexes of the tropocoronand macrocycles

Article abstract of DOI:10.1021/om00154a025

The synthesis, characterization, and chemical properties of alkyne-bridged binuclear copper(I) tropocoronand complexes are described. Two methods, employing labile copper(I) acetonitrile or carbon monoxide intermediates, were used to prepare [Cu₂(μ-DEAD)(TC-6,6)] (1) and [Cu₂(μ-DMAD)(TC-6,6)] (2), where DEAD and DMAD are the diethyl and dimethyl esters of acetylenedicarboxylic acid, respectively, and TC-6,6 is the tropocoronand ligand having six methylene groups in the two linker chains connecting the aminotroponeiminate poles of the macrocycle. The diaryl- and dialkyl-substituted alkyne complexes [Cu₂(μ-PhC≡CPh)(TC-6,6)] (3) and [Cu₂(μ-CH₃C≡CCH₃)(TC-6,6)] (4) were synthesized directly by a third route in which the Cu₂(TC-6,6) unit was generated in the presence of excess alkyne. The novel alkyne-bridged dicopper(I) complexes were characterized by UV-vis, infrared, proton, and carbon-13 NMR spectroscopy and, in the case of 1 and 2, by X-ray diffraction. The molecular structures reveal the alkyne positioned above and perpendicular to the copper-copper vector. The Cu?Cu distances are 2.806 (1) and 2.788 (1) A?, the average Cu-C bond lengths are 1.946 (5) and 1.942 (7) A?, and the C≡C bond lengths are 1.320 (6) and 1.314 (9) A? for 1 and 2, respectively. The unit cell parameters of 3 are also reported. These compounds exhibit unusual stability both in the solid state and in solution, being unreactive toward air oxidation (except for 4), hydrogenation, and nucleophilic attack, and in attempted cycloaddition and cyclopentenone annelation reactions.