The conversion of a variety of well‐known test reactions, representing the key reactivity patterns of gold catalysis, were analyzed by GC and 1H NMR. The study is focused on establishing of a strategical approach for the consideration of ligand influence and counter anion influence during the catalyst optimization including an industrial perspective. The study shows a dominance of the counter anion, a dominance which up to now has been neglected in most of the routine screenings. In addition, a drastic substrate‐dependency became obvious, even a marginal variation of the substrate already could strongly effect the catalytic activity and change the optimal counter anion or ligand. Based on the collected data a strategic concept for an efficient screening for a specific substrate is introduced, this concept can serve as an important guideline for catalyst optimization in homogeneous gold catalysis.magnified image

A comparison of versatile counter anions was investigated by means of a variety of well‐known test reactions representing the key reactivity patterns of homogeneous gold catalysis, the catalytic activity was monitored by GC and 1H NMR. As previously reported, the counter anion influence is usually more pronounced than the corresponding ligand effect. Due to this, the study is focused on the investigation of counter anions so far not included from investigation of homogeneous gold‐catalyzed reactions. The examinations using so far neglected counter anions (BArF4)−, [B(C6F5)4]−, [Al(OC(CF3)3)4]− and [B(C6F5)3(OAcF)]− showed surpassing or at least similar catalytic activities as the commonly used counter anions. The expanded use of counter anions can occupy an important role in future concerning catalyst optimization in gold catalysis.magnified image

By using silver complexes with bulky ligands such as DavePhos or N-heterocyclic carbenes, propargylic alcohols are smoothly converted with CO2 into a unique class of unexplored cyclic alkylidene carbonates. These systems, for the first time, also achieve the direct carboxylative cyclization of primary propargylic alcohols. The silver-DavePhos catalyst is further applied for the bis-carboxylative cyclization of primary propargyl derivatives, thereby providing an effective route to a series of previously inaccessible and industrially relevant α-alkylidene cyclic carbonates.

An extensive kinetic study of selected key reactions of (oxidative) gold catalysis concentrates on the decrease of the catalytic activity due to inhibition of the gold(I) catalyst caused by pyridine derivatives that are obtained as by-products if N-oxides are applied as oxygen donors. The choice of the examined pyridine derivatives and their corresponding N-oxides has been made regardless of their commercial availability; particular attention has been paid to the practical benefit which up to now has been neglected in most of the reaction screenings. The test reactions were monitored by GC and 1 H NMR spectroscopy. The received reaction constants provide information concerning a correlation between the electronic structure of the heterocycle and the catalytic activity. Based on the collected kinetic data, it was possible to develop a basic set of three N-oxides which have to be taken into account in further oxidative gold(I)-catalyzed reactions.

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Following the modular template synthesis using isonitriles,n ew unsymmetrically substituted five-membered saturated N-heterocyclic carbene (NHC)a nd N-heterocyclic oxo-carbene (NHOC) gold(I) complexes were prepared. With these species and already reported complexes,adetailed study concerning the catalytic activities of the complex classes available by the isonitrile routew as conducted. Thec atalytic properties of twelve different types of NHOCs, saturated and unsaturated NHC gold(I) pre-catalysts with different substituents,a sw ella s one representative of as ix-membered NHC and one N-acyclic carbene (NAC)g old(I) complex were analyzed by utilizing the phenol synthesisa satest reaction. Fort his reaction, the saturated NHC gold(I) complexes achieved higher conversions than the corresponding unsaturated NHCs andt he NHOC systems.W hile unsaturated NHC complexes show higher catalytic activity during the initial phase of the conversion, due to ah igher stability,h igher turnover numbers( TONs) were obtained for the corresponding saturated systems.Acyclopentadecyls ubstituenta tn itrogen turned out to be the privileged substituent for all of the unsymmetrical complexes. Furthermore,w ed etectedt hat light exclusion can significantly increase the catalytic activity of NHC gold(I) complexes for phenols ynthesis.

A gold(I)‐catalyzed cascade cyclization–alkynylation of allenoates using alkynyl bromide to generate β‐alkynyl‐γ‐butenolides was investigated. Whereas alkynyl iodides afforded significant amounts of the homo‐coupling of two lactone units, alkynyl bromides led to a selective reaction, and a broad functional group tolerance was observed. Under the optimized reaction conditions, it was possible to directly synthesize a large range of β‐alkynyl‐γ‐butenolides in moderate to good yields without the need for any external oxidant.

Theg old-catalyzed mono-hydroarylation and two-fold hydroarylation of alkynes with electron-rich heteroarenes was analyzed by a 1 HNMR kinetic study. Theo btainedr ate constants for the decreasing alkyne concentration provide information on the reactivity of this addition reaction. Thee xaminations show the orthogonal reactivity of gold and ap roton for the twor eactions teps.T he first hydroarylation is exclusively promoted by gold(I), whereast he second step is premised on ap roton which will be reversibly derivedf rom the formation of s,p-acetylide complexes from the terminal alkynes or by interaction with solvents.B ased on kinetic data, it was possible to synthesizeal arger ange of mono-adducts in moderate to good yields,f urthermore the synthesiso fh etero-di-adducts,b earing two different substituents,w as explored.