The copper-mediated aromatic nucleophilic substitution reactions developed by Fritz Ullmann and Irma Goldberg required stoichiometric amounts of copper and very high reaction temperatures. Recently, it was found that addition of relatively cheap ligands (diamines, aminoalcohols, diketones, diols) made these reactions truly catalytic, with catalyst amounts as low as 1 mol% or even lower. Since these catalysts are homogeneous, it has opened up the possibility to investigate the mechanism of these modified Ullmann reactions. Most authors agree that Cu(I) is the true catalyst even though Cu(0) and Cu(II) catalysts have also shown to be active. It should be noted however that Cu(I) is capable of reversible disproportionation into Cu(0) and Cu(II). In the first step, the nucleophile displaces the halide in the LnCu(I)X complex forming LnCu(I)ZR (Z = O, NR¢, S). Quite a number of mechanisms have been proposed for the actual reaction of this complex with the aryl halide: 1. Oxidative addition of ArX forming a Cu(III) intermediate followed by reductive elimination; 2. Sigma bond metathesis; in this mechanism copper remains in the Cu(II) oxidation state; 3. Single electron transfer (SET) in which a radical anion of the aryl halide is formed (Cu(I)/Cu(II)); 4. Iodine atom transfer (IAT) to give the aryl radical (Cu(I)/Cu(II)); 5. p-complexation of the aryl halide with the Cu(I) complex, which is thought to enable the nucleophilic substitution reaction. Initially, the radical type mechanisms 3 and 4 where discounted based on the fact that radical clock-type experiments with ortho-allyl aryl halides failed to give the cyclised products. However, a recent DFT study by Houk, Buchwald and co-workers shows that the modified Ullmann reaction between aryl iodide and amines or primary alcohols proceeds either via an SET or an IAT mechanism. Van Koten has shown that stalled aminations can be rejuvenated by the addition of Cu(0), which serves to reduce the formed Cu(II) to Cu(I); this also corroborates a Cu(I)/Cu(II) mechanism. Thus the use of radical clock type experiments in these metal catalysed reactions is not reliable. DFT calculations from Hartwig seem to confirm a Cu(I)/Cu(III) type mechanism for the amidation (Goldberg) reaction, although not all possible mechanisms were calculated.

A protocol for the copper-catalyzed aryl-sulfur bond formation between aryl iodides and thiophenols is reported. The reaction is catalyzed by a low amount (1-2.5 mol %) of readily available and ligand-free copper iodide salt. A variety of diaryl thioethers are synthesized under relatively mild reaction conditions with good chemoselectivity and functional group tolerance.

a b s t r a c tA small library of 2-aminoarenethiolato-copper(I) (CuSAr) complexes was tested as (pre-)catalysts in the arylation reaction of phenols with aryl bromides. These copper(I) (pre-)catalysts are thermally stable, soluble in common organic solvents, and allow reactions of 6 h at 160 C with low catalyst loadings of 2.5 mol %. Among the (pre-)catalysts screened, 2-[(dimethylamino)methyl]benzenethiolato-copper(I) (1c) led to the best results and provided good to excellent yields of various substituted diaryl ethers. Mechanistic studies showed that at early stages of the CeO coupling reaction the CuSAr complex is converted into CuBr(PhSAr) via selective coupling of the monoanionic arenethiolato ligand with phenyl bromide with formation of CuBr. In addition, the first results are shown involving a multi-component reaction (MCR) protocol for the in situ synthesis of propargylamines and their subsequent conversion involving a CeO cross coupling reaction. Furthermore, two examples of sequential CeO/CeS and CeN/ CeS cross coupling reactions have been carried out on the same dihalo-pyridine substrate in a one-pot process with the same (CuSAr) (pre-)catalyst (overall yields 40e80%).

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Protein resistant polymer brushes of poly(diethylene glycol methylether methacrylate) (DEGMA) are synthesized by surface‐initiated polymerization (SIP) on gold and are thoroughly characterized with particular attention to the nanomechanical properties. Compared to the well known brushes of poly(oligoethylene glycol methylether methacrylate) (POEGMA) on gold, PDEGMA brushes grow faster and yield higher final brush heights. In confocal fluorescence microscopy experiments it is shown that both types of brushes possess similar low non‐specific adsorption levels of labeled bovine serum albumin (BSA) from buffer. While the surface stiffness evaluated by depth sensing indentation in the dry state suggests that side chain crystallization imparts high stiffness to the POEGMA brush, PDEGMA brushes behave similar to poly(methyl methacrylate) (PMMA) brushes of comparable thickness. In the wet state PDEGMA brushes are shown to possess an elastic modulus of 800 kPa, as estimated by AFM nanoindentation, which is smaller than that of POEGMA (3 000 kPa). Expanding these brushes to end‐functional polymers with recently developed block copolymer brush approaches, tailored soft biointerfaces can be generated for cell ‐ surface interaction and cell culture studies.