We present a study on the catalytic activity of platinum nanoparticles immobilized on spherical polyelectrolyte brushes that act as carriers. The spherical polyelectrolyte brushes consist of a solid core of poly(styrene) onto which long chains of poly(2-methylpropenoyloxyethyl) trimethylammonium chloride are grafted. These positively charged chains form a dense layer of polyelectrolytes on the surface of the core particles ("spherical polyelectrolyte brush") that tightly binds divalent PtCl6-(2) ions. The reduction of these ions within the brush layer leads to nearly monodisperse nanoparticles of metallic platinum. The average size of the particles is approximately 2 nm. The composite particles exhibit excellent colloidal stability. The catalytic activity is investigated by photometrically monitoring the reduction of p-nitrophenol by an excess of NaBH4 in the presence of the nanoparticles. The kinetic data could be explained by the assumption of a pseudo-first-order reaction with regard to p-nitrophenol. In all cases, a delay time t0 has been observed, after which the reactions start. This time is shorter when the catalyst has already been used. All data demonstrate that spherical polyelectrolyte brushes present an ideal carrier system for metallic nanoparticles.

The conservation of our element resources is a fundamental challenge of mankind. The development of alcohol refunctionalization reactions is a possible fossil carbon conservation strategy since alcohols can be obtained from indigestible and abundantly available biomass. The conservation of our rare noble metals, frequently used in key technologies such as catalysis, might be feasible by replacing them with highly abundant metals. The alkylation of amines by alcohols and related C–C coupling reactions are early examples of alcohol refunctionalization reactions. These reactions follow mostly the borrowing hydrogen or hydrogen autotransfer catalysis concept, and many 3d-metal catalysts have been disclosed in recent years. In this review, we summarize the progress made in developing Cu, Ni, Co, Fe, and Mn catalysts for C–N and C–C bond formation reactions with alcohols and amines using the borrowing hydrogen or hydrogen autotransfer concept. We expect that the findings in this field will inspire others to develop new efficient and selective earth-abundant metal catalysts for borrowing hydrogen or hydrogen autotransfer applications or to develop novel alcohol refunctionalization reactions that can be mediated by such metals.

The pyrrole heterocycle is a prominent chemical motif and is found widely in natural products, drugs, catalysts and advanced materials. Here we introduce a sustainable iridium-catalysed pyrrole synthesis in which secondary alcohols and amino alcohols are deoxygenated and linked selectively via the formation of C-N and C-C bonds. Two equivalents of hydrogen gas are eliminated in the course of the reaction, and alcohols based entirely on renewable resources can be used as starting materials. The catalytic synthesis protocol tolerates a large variety of functional groups, which includes olefins, chlorides, bromides, organometallic moieties, amines and hydroxyl groups. We have developed a catalyst that operates efficiently under mild conditions.

Homogeneous alloy nanoparticles as excellent catalysts. Spherical polyelectrolyte brushes can be used to generate Au‐Pt alloy nanoparticles (see figure) that exhibit properties widely differing from the properties of the respective bulk alloys. The alloy nanoparticles are shown to be homogeneous solid solutions. Moreover, they are effective catalysts for the selective oxidation of alcohols to aldehydes and ketones.

The implementation of inexpensive, Earth-abundant metals in typical noble-metal-mediated chemistry is a major goal in homogeneous catalysis. A sustainable or green reaction that has received a lot of attention in recent years and is preferentially catalyzed by Ir or Ru complexes is the alkylation of amines by alcohols. It is based on the borrowing hydrogen or hydrogen autotransfer concept. Herein, we report on the Co-catalyzed alkylation of aromatic amines by alcohols. The reaction proceeds under mild conditions, and selectively generates monoalkylated amines. The observed selectivity allows the synthesis of unsymmetrically substituted diamines. A novel Co complex stabilized by a PN5 P ligand catalyzes the reactions most efficiently.

The gas-phase loading of [Zn(4)O(btb)(2)](8) (MOF-177; H(3)btb=1,3,5-benzenetribenzoic acid) with the volatile platinum precursor [Me(3)PtCp'] (Cp'=methylcyclopentadienyl) was confirmed by solid state (13)C magic angle spinning (MAS)-NMR spectroscopy. Subsequent reduction of the inclusion compound [Me(3)PtCp'](4)@MOF-177 by hydrogen at 100 bar and 100 degrees C for 24 h was carried out and gave rise to the formation of platinum nanoparticles in a size regime of 2-5 nm embedded in the unchanged MOF-177 host lattice as confirmed by transmission electron microscopy (TEM) micrographs and powder X-ray diffraction (PXRD). The room-temperature hydrogen adsorption of Pt@MOF-177 has been followed in a gravimetric fashion (magnetic suspension balance) and shows almost 2.5 wt % in the first cycle, but is decreased down to 0.5 wt % in consecutive cycles. The catalytic activity of Pt@MOF-177 towards the solvent- and base-free room temperature oxidation of alcohols in air has been tested and shows Pt@MOF-177 to be an efficient catalyst in the oxidation of alcohols.

The sustainable use of the resources on our planet is essential. Noble metals are very rare and are diversely used in key technologies, such as catalysis. Manganese is the third most abundant transition metal of the Earth's crust and based on the recently discovered impressive reactivity in hydrogenation and dehydrogenation reactions, is a potentially useful noble-metal "replacement". The hope of novel selectivity profiles, not possible with noble metals, is also an aim of such a "replacement". The reactivity of manganese complexes in (de)hydrogenation reactions was demonstrated for the first time in 2016. Herein, we summarize the work that has been published since then and especially discuss the importance of homogeneous manganese catalysts in comparison to cobalt and iron catalysts.

Thermosensitive core-shell microgels can be used as ''nanoreactors'' for the immobilization of metal nanoparticles. The microgels consist of a polystyrene core and a network made of poly(Nisopropylacrylamide) (PNIPA) cross-linked by N,N 0 -methylenebisacrylamide. The cross-linked PNIPA shell undergoes a volume transition at around 30 C in which most of the water is expelled. The microgel particles exhibit a weak positive charge due to the cationic initiator. Metal nanoparticles (such as Au, Rh and Pt) with high catalytic activity can be homogeneously embedded into such a network. The oxidation of alcohols to the corresponding aldehydes or ketones has been chosen as a test reaction to probe the catalytic activity of such metal-microgel nanocomposite particles