No abstract

Catalytic reductions of carbonyl‐containing compounds are highly important for the safe, sustainable, and economical production of alcohols. Herein, we report on the efficient transfer hydrogenation of ketones catalyzed by a highly potent Mn(I)−NHC complex. Mn−NHC 1 is practical at metal concentrations as low as 75 ppm, thus approaching loadings more conventionally reserved for noble metal based systems. With these low Mn concentrations, catalyst deactivation is found to be highly temperature dependent and becomes especially prominent at increased reaction temperature. Ultimately, understanding of deactivation pathways could help close the activity/stability‐gap with Ru and Ir catalysts towards the practical implementation of sustainable earth‐abundant Mn‐complexes.

Any catalyst should be efficient and stable to be implemented in practice. This requirement is particularly valid for manganese hydrogenation catalysts. While representing a more sustainable alternative to conventional noble metal-based systems, manganese hydrogenation catalysts are prone to degrade under catalytic conditions once operation temperatures are high. Herein, we report a highly efficient Mn(I)-CNP pre-catalyst which gives rise to the excellent productivity (TOF° up to 41 000 h−1) and stability (TON up to 200 000) in hydrogenation catalysis. This system enables near-quantitative hydrogenation of ketones, imines, aldehydes and formate esters at the catalyst loadings as low as 5–200 p.p.m. Our analysis points to the crucial role of the catalyst activation step for the catalytic performance and stability of the system. While conventional activation employing alkoxide bases can ultimately provide catalytically competent species under hydrogen atmosphere, activation of Mn(I) pre-catalyst with hydride donor promoters, e.g. KHBEt3, dramatically improves catalytic performance of the system and eliminates induction times associated with slow catalyst activation.

The experimental electron density of sumanene, C(21)H(12), was extracted from a high resolution X-ray data set measured at 100 K and topologically analyzed. In addition to bond topological and atomic properties, information about the density distribution between adjacent molecules, which show close C···C approaches of ~3.4 Å within the columnar π-stacks in the crystal lattice, are discussed. A comparison is made with the electron density of the related corannulene molecule based also on the analysis of Electron Localizability Indicator (ELI-D) calculations.

In the crystal structures of the two organic salts, namely, pyrimethamine hydrogen glutarate (1:1) 1 and pyrimethamine formate (1:1) 2, the pyrimethamine moieties are protonated at one of the nitrogen atoms of the pyrimidine rings. The carboxylate group of the respective anions (hydrogen glutarate and formate) interacts with the protonated pyrimidine moiety in a near linear fashion through a pair of N−H···O hydrogen bonds. The dihedral angle between the diaminopyrimidine and the p-chlorophenyl plane is 74.8(1)° in compound 1, and the corresponding value in compound 2 is 76.7(1)°. In both compounds, the pyrimidine moieties are centrosymmetrically paired through a pair of N−H···N hydrogen bonds. The 2-amino group of the one member of the pair and the 4-amino group of the other member are bridged by an O atom of the carboxylate group, using a pair of N−H···O hydrogen bonds. This combination of hydrogen bonds results in the complementary DADA (D = donor and A = acceptor in hydrogen bonds) arrays of quadruple hydrogen-bonding patterns. In compound 1, there are chains and ladders made up of the O−H···O, N−H···O, and C−H···N hydrogen bonds whereas compound 2 displays a three-dimensional network of hydrogen bonds.