The thiolate-for-thiolate ligand exchange reaction between the stable Au(38)(2-PET)(24) and Au(40)(2-PET)(24) (2-PET: 2-phenylethanethiol) clusters and enantiopure BINAS (BINAS: 1,1'-binaphthyl-2,2'-dithiol) was investigated by circular dichroism (CD) spectroscopy in the UV/vis and MALDI mass spectrometry (MS). The ligand exchange reaction is incomplete, although a strong optical activity is induced to the resulting clusters. The clusters are found to be relatively stable, in contrast to similar reactions on [Au(25)(2-PET)(18)](-) clusters. Maximum anisotropy factors of 6.6 × 10(-4) are found after 150 h of reaction time. During the reaction, a varying ratio between Au(38) and Au(40) clusters is found, which significantly differs from the starting material. As compared to Au(38), Au(40) is more favorable to incorporate BINAS into its ligand shell. After 150 h of reaction time, an average of 1.5 and 4.5 BINAS ligands is found for Au(38) and Au(40) clusters, respectively. This corresponds to exchange of 3 and 9 monodentate 2-PET ligands. To show that the limited exchange with BINAS is due to the bidentate nature of the ligand, exchange with thiophenol was performed. The monodentate thiophenol exchange was found to be faster, and more ligands were exchanged when compared to BINAS.

It is better to light a candle than to curse the dark. AbstractThe 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) 2 Cu]PF 6 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 m-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 mo-

A copper(I)‐catalyzed carboxylation of terminal alkynes followed trapping of the carboxylate with methyl iodide provides a straightforward access to 3‐substituted methyl propiolates that can be reacted in the same reaction vessel in a consecutive fashion to give 2,6‐disubstituted pyrimid‐4(3H)‐ones and 1,5‐disubstituted 3‐hydroxypyrazoles in moderate to good yields. The Cu(I)‐catalyzed carboxylation with carbon dioxide as C1 source therefore provides an environmentally benign entry to three‐carbon building blocks in heterocyclic synthesis.

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