Methanol synthesis from syngas (CO/H 2 mixtures) is one of the largest manmade chemical processes with annual production reaching 100 million tons. The current industrial method proceeds at high temperatures (200−300 °C) and pressures (50−100 atm) using a copper−zinc-based heterogeneous catalyst. In contrast, here, we report a molecularly defined manganese catalyst that allows for low-temperature/lowpressure (120−150 °C, 50 bar) carbon monoxide hydrogenation to methanol. This new approach was evaluated and optimized by quantum mechanical simulations virtual high-throughput screenings. Crucial for this achievement is the use of amine-based promoters, which capture carbon monoxide to give formamide intermediates, which then undergo manganese-catalyzed hydrogenolysis, regenerating the promoter. Following this conceptually new approach, high selectivity toward methanol and catalyst turnover numbers (up to 3170) was achieved. The proposed general catalytic cycle for methanol synthesis is supported by model studies and detailed spectroscopic investigations.
Recently, pentlandite
materials have been shown to exhibit promising
properties with respect to the hydrogen evolution reaction (HER).
A whole series of trimetallic FeCoNi-pentlandite materials and composites
have been synthesized from the elements using high-temperature synthesis
and categorized in terms of purity. Furthermore, the electrocatalytic
properties regarding the HER were determined and correlated to hydrogen
adsorption energies, which were determined by means of density functional
theory (DFT) calculations. The relationships between activity and
its origin generated in this way help to better understand the pentlandite
system and provide meaningful approaches for catalyst synthesis.
The
cascade reactions of carbohydrates with methyl ketones in the
presence of proline feature complex running reaction steps. By extensive
quantum mechanical simulation, a coherent reaction mechanism was identified
matching the experimental data. The present calculations indicate
a Mannich reaction/proline hydrolysis/retro aza-Michael cascade to
form an intermediate α,β-unsaturated ethyl ketone. This
key precursor yields C-glycosides by a final intramolecular
amine-catalyzed oxa-Michael addition. Additionally, the formation
of this intermediate determines the rate and selectivity of the overall
cascade reaction. Strongly matched and mismatched cases were observed
when used with d- or l-proline. They are consistent
with the calculated energy barriers of the corresponding transition
states.
We describe the results of our quantum mechanical investigation of the asymmetric hydrogenation of β-ketoesters catalyzed by [RuCl 2 (MeOH) 2 ((R)-MeOBIPHEP)] (7 a), which is generated in situ from [Ru(OAc) 2 ((R)-MeOBIPHEP)] (4 a) and HCl in methanol. Interestingly, HCl not only acts as an activator for 4 a as it has a dramatic effect on the reaction itself: While HCl/4 a = 2 leads to rather poor results (36 % ee and 13 % conv. after 4 h at at a substrate-to-catalyst ratio (S/C) = 50'000), HCl/4 a = 20 results in high efficiency (> 99.9 % conv.) and enantioselectivity (99 % ee favoring the opposite enantiomer) under otherwise identical conditions. The origin for this sweeping change in performance has remained a mystery for two decades. Here, we show for the first time that a highly selective HCl pathway becomes operational under acidic conditions, which outcompetes moderately selective pathways dominating under neutral conditions. Furthermore, we explain the effects of common phosphorus substituents on the activity of the catalyst.
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