%0 Generic
%A Berg, Regina
%C Heidelberg
%D 2013
%F heidok:15202
%R 10.11588/heidok.00015202
%T Highly Active Dinuclear Copper Catalysts for Homogeneous Azide-Alkyne Cycloadditions
%U https://archiv.ub.uni-heidelberg.de/volltextserver/15202/
%X The copper-catalyzed azide-alkyne cycloaddition for the synthesis of 1,4-disubstituted 1,2,3-triazoles (CuAAC) is a variant of Huisgen’s 1,3-dipolar cycloaddition which disburdens the thermal reaction from its major drawbacks such as poor regioselectivity, long reaction times and harsh conditions. In contrast to the widely used “black box” reagent mixtures, a molecularly defined, highly active catalyst system for homogeneous CuAAC reactions has been developed in this PhD project. In dependence on the postulated stepwise mechanism, its most important structural feature is the presence of two copper(I) ions irreversibly bound in the same catalyst molecule. A highly modular and profitable synthesis for bistriazolium hexafluorophosphate salts as precursors for the ancillary ligand system was devised. In analogy to the CuAAC catalyst systems of general formula [(NHC)2Cu]PF6 described in literature, novel dinuclear copper(I) complexes with a bistriazolylidene ligand backbone and 1,3-bis(2,6-diisopropylphenyl)-imidazol-2-ylidene (IPr) as sacrificial ligand were prepared. However, these complexes did not show the expected high catalytic activity, most probably due to the strong coordination of the IPr ligands. In consequence, another family of dinuclear copper(I) complexes with µ-coordinated acetate as labile ligand was synthesized by reaction of the bistriazolium hexafluorophosphate ligand precursors with copper(I) acetate in the presence of a base. The broad applicability and high catalytic activity of one of these bistriazolylidene dicopper acetate complexes was confirmed by a series of gaschromatographically monitored CuAAC reactions in different solvents and with various substrates. The order of reaction with respect to the initial concentration of the precatalyst was investigated by determination of the half value periods of reactions with different concentrations of the dinuclear copper acetate complex. The results of these kinetic experiments with phenylacetylene and ethyl propiolate were rationalized by postulating different catalyst resting states and rate-determining steps in dependence on the properties of the alkyne substrate. Direct evidence of a dinuclear copper acetylide intermediate in the CuAAC reaction’s mechanism was gained by NMR spectroscopy and mass spectrometry.