The complex [Ru(Triphos)(TMM)] (Triphos = 1,1,1-tris(diphenylphosphinomethyl)ethane, TMM = trimethylene methane) provides an efficient catalytic system for the hydrogenation of a broad range of challenging functionalities encompassing carboxylic esters, amides, carboxylic acids, carbonates, and urea derivatives. The key control factor for this unique substrate scope results from selective activation to generate either the neutral species [Ru(Triphos)(Solvent)H2] or the cationic intermediate [Ru(Triphos)(Solvent)(H)(H2)](+) in the presence of an acid additive. Multinuclear NMR spectroscopic studies demonstrated together with DFT investigations that the neutral species generally provides lower energy pathways for the multistep reduction cascades comprising hydrogen transfer to C═O groups and C-O bond cleavage. Carboxylic esters, lactones, anhydrides, secondary amides, and carboxylic acids were hydrogenated in good to excellent yields under these conditions. The formation of the catalytically inactive complexes [Ru(Triphos)(CO)H2] and [Ru(Triphos)(μ-H)]2 was identified as major deactivation pathways. The former complex results from substrate-dependent decarbonylation and constitutes a major limitation for the substrate scope under the neutral conditions. The deactivation via the carbonyl complex can be suppressed by addition of catalytic amounts of acids comprising non-coordinating anions such as HNTf2 (bis(trifluoromethane)sulfonimide). Although the corresponding cationic cycle shows higher overall barriers of activation, it provides a powerful hydrogenation pathway at elevated temperatures, enabling the selective reduction of primary amides, carbonates, and ureas in high yields. Thus, the complex [Ru(Triphos)(TMM)] provides a unique platform for the rational selection of reaction conditions for the selective hydrogenation of challenging functional groups and opens novel synthetic pathways for the utilization of renewable carbon sources.

A happy marriage of two processes: An effective catalytic system was identified for the direct synthesis of carboxylic acids from non‐activated olefins or alcohols, CO2, and H2. Detailed analysis together with labeling studies indicated that the overall hydrocarboxylation of simple olefins results from a combination of the reverse water–gas shift (rWGS) reaction and a hydroxycarbonylation step, each promoted by a rhodium catalyst (see scheme).

Rheotaxis and migration of cells in a flow field have been investigated intensively owing to their importance in biology, physiology and engineering. In this study, first, we report our experiments showing that the microalgae Chlamydomonas can orient against the channel flow and migrate to the channel centre. Second, by performing boundary element simulations, we demonstrate that the mechanism of the observed rheotaxis and migration has a physical origin. Last, using a simple analytical model, we reveal the novel physical mechanisms of rheotaxis and migration, specifically the interplay between cyclic body deformation and cyclic swimming velocity in the channel flow. The discovered mechanism can be as important as phototaxis and gravitaxis, and likely plays a role in the movement of other natural microswimmers and artificial microrobots with non-reciprocal body deformation.

Selective introduction of methyl branches into the carbon chains of alcohols can be achieved with low loadings of ruthenium precatalyst [RuH(CO)(BH4)(HN(C2H4PPh2)2)] (Ru‐MACHO‐BH) using methanol both as methylating reagent and as reaction medium. A wide range of structurally divers alcohols was β‐methylated with excellent selectivity (>99 %) in fair to high yields (up to 94 %) under standard conditions, and turnover numbers up to 18,000 could be established. The overall reaction rate of the complex catalytic network appears to be governed by interconnection of the individual subcycles through availability of the reactive intermediates. The synthetic procedure opens pathways to important structural motifs following the Green Chemistry principles.

Selective β-methylation of alcohols with methanol has been recently described using a catalytic system comprising the ruthenium pincer complex [RuH(CO)(BH 4 )(HN(C 2 H 4 PPh 2 ) 2 )]-(Ru-MACHO-BH) 1 and alcoholate bases as co-catalysts. [1] Here we present a detailed mechanistic analysis for the mono-methylation of 1-phenyl-propane-1-ol 2 a as prototypical example. Several experimentally observed intermediates were localized as stable minima on the DFT-derived energy surface of the entire reaction network. The ruthenium complex [Ru(H) 2 (CO) (HN(C 2 H 4 PPh 2 ) 2 )] I was inferred as the active species catalyzing the de-hydrogenation/re-hydrogenation of substrates and intermediates ("hydrogen borrowing"). The hydrogen-bonded alcohol adduct of this complex was identified as the lowest lying intermediate (TDI). The CÀ C bond formation results from a base-catalyzed aldol reaction comprising the transition state with the highest energy (TDTS). Experimentally determined Gibbs free activation barriers of 26.1 kcal/mol and 26.0 kcal/mol in methanol and toluene as solvents, respectively, are reflected well by the computed energy span of the complex reaction network (29.2 kcal/mol).Catalytic methods for the introduction of methyl groups into organic substrates using methanol as C1 building block offer attractive synthetic pathways in line with the principles of Green Chemistry. In particular the synthesis of methyl branches in aliphatic carbon chains using methanol remains a significant challenge, however. [2] Most recently we showed that ruthenium pincer complex [RuH(CO)(BH 4 )(HN(C 2 H 4 PPh 2 ) 2 )]-(Ru-MACHO-BH) 1 is a versatile pre-catalyst for this reaction. [1] For a broad range of primary and secondary alcohols as substrates, the methyl group is introduced selectively in βposition providing the branched products in good to very high yields with water as the only byproduct (Scheme 1). The synthetic methodology has been transferred and largely extended by the use of Mn(I)-MACHO complex most recently. [3] In this work we present a mechanistic analysis of this transformation with the original ruthenium catalyst based on experimentally and theoretically compiled data.From the results of the synthetic studies, we postulated a working hypothesis for the catalytic process exemplified in Scheme 2 for the mono-methylation of 1-phenyl-propane-1-ol 2 a to 1-phenyl-2-methyl-propane-1-ol 3 a. The overall trans-formation involves five individual cycles A-E forming a complex reaction network. Initially both alcohol and methanol are dehydrogenated by the transition metal catalyst to form ketone and formaldehyde, respectively. [4] Subsequently, a base-catalyzed aldol condensation generates the CÀ C bond [5] and finally the unsaturated intermediate is step-wise re-hydrogenated at the ruthenium catalyst.The involvement of the de-and re-hydrogenation cycles is corroborated with a series of control experiments summarized in scheme 3. 1-phenyl-propane-1-ol 2 a reacts with 13 CH 3 OH to the mono-methylated product containing the 13 ...