Base‐metal catalysis, especially with non‐noble‐metal pincer‐type catalysts, is increasingly used in organic synthesis and thus becoming more and more important for organometallic chemistry. After ...ruthenium‐, iridium‐ and iron‐based pincer‐type complexes became established as state‐of‐the‐art catalysts for (de)hydrogenation reactions in the past decade, manganese complexes have most recently been successfully applied in related transformations. Specifically, this microreview covers their recent progress in (de)hydrogenation and transfer (de)hydrogenation as well as in C–C and C–X bond‐forming reactions.
We focus here on the development and synthesis of manganese‐based pincer‐type catalysts and on recent progress in their application. As well as for hydrogenations, we describe their utilisation for dehydrogenation, hydrosilylation, hydroboration and transfer (de)hydrogenation reactions. Additionally, the usage of manganese‐based pincer complexes for C–C, C–N and C–O bond transformations is highlighted.
The first manganese‐catalyzed hydrogenation of esters to alcohols has been developed. The combination of Mn(CO)5Br with HN(CH2CH2P(Et)2)2 leads to a mixture of cationic and neutral Mn PNP pincer ...complexes, which enable the reduction of various ester substrates, including aromatic and aliphatic esters as well as diesters and lactones. Notably, related pincer complexes with isopropyl or cyclohexyl substituents showed very low activity.
A manganese‐catalyzed hydrogenation of esters to alcohols has been developed. The combination of Mn(CO)5Br with HN(CH2CH2P(Et)2)2 led to a cationic and a neutral Mn PNP pincer complex, which both enable the reduction of various aromatic and aliphatic esters as well as diesters and lactones.
For the first time, structurally defined manganese pincer complexes catalyze the dehydrogenation of aqueous methanol to hydrogen and carbon dioxide, which is a transformation of interest with regard ...to the implementation of a hydrogen and methanol economy. Excellent long‐term stability was demonstrated for the Mn‐PNPiPr catalyst, as a turnover of more than 20 000 was reached. In addition to methanol, other important hydrogen carriers were also successfully dehydrogenated.
Just a pinch: A molecularly defined manganese PNP pincer complex selectively dehydrogenates methanol to hydrogen and carbon dioxide at low temperature. Remarkable stability and an excellent turnover (TON) of more than 20 000 was achieved.
Phloem sap contains a large number of macromolecules, including proteins and RNAs from different classes. Proteome analyses of phloem samples from different plant species under denaturing conditions ...identified hundreds of proteins potentially involved in diverse processes.
Surprisingly, these studies also found a significant number of ribosomal and proteasomal proteins. This led to the suggestion that active ribosome and proteasome complexes might be present in the phloem, challenging the paradigm that protein synthesis and turnover are absent from the enucleate sieve elements of angiosperms. However, the existence of such complexes has as yet not been demonstrated.
In this study we used three-dimensional gel electrophoresis to separate several protein complexes from native phloem sap from Brassica napus. Matrix-assisted laser desorption ionization-time of flight MS analyses identified more than 100 proteins in the three major protein-containing complexes.
All three complexes contained proteins belonging to different ribosomal fragments and blue native northern blot confirmed the existence of ribonucleoprotein complexes. In addition, one complex contained proteasome components and further functional analyses confirmed activity of a proteasomal degradation pathway and showed a large number of ubiquitinated phloem proteins.
Our results suggest specialized roles for ubiquitin modification and proteasome-mediated degradation in the phloem.
A new chiral manganese PNP pincer complex is described. The asymmetric hydrogenation of several prochiral ketones with molecular hydrogen in the presence of this complex proceeds under mild ...conditions (30–40 °C, 4 h, 30 bar H2). Besides high catalytic activity for aromatic substrates, aliphatic ketones are hydrogenated with remarkable selectivity (e.r. up to 92:8). DFT calculations support an outer sphere hydrogenation mechanism as well as the experimentally determined stereochemistry.
In a pinch: A new type of chiral manganese pincer complex (C gray, H white, Mn blue, N green, O red, P magenta) was developed and applied for the reduction of aromatic and aliphatic ketones. The asymmetric hydrogenation of several prochiral ketones with molecular hydrogen in the presence of this complex proceeds under mild conditions (30–40 °C, 4 h, 30 bar H2).
The first manganese‐catalyzed hydrogenation of esters to alcohols has been developed. The combination of Mn(CO)5Br with HN(CH2CH2P(Et)2)2 leads to a mixture of cationic and neutral Mn PNP pincer ...complexes, which enable the reduction of various ester substrates, including aromatic and aliphatic esters as well as diesters and lactones. Notably, related pincer complexes with isopropyl or cyclohexyl substituents showed very low activity.
Eine Mangan‐katalysierte Hydrierung von Estern zu Alkoholen wurde entwickelt. Die Kombination von Mn(CO)5Br mit HN(CH2CH2P(Et)2)2 führt zur Bildung eines kationischen und eines neutralen Mn‐PNP‐Pincerkomplexes, die beide die Reduktion von aromatischen und aliphatischen Estern sowie Diestern und Lactonen katalysieren.
The synthesis of different metal pincer complexes coordinating to the chiral PNP ligand bis(2‐((2R,5R)‐2,5‐dimethyl‐phospholanoethyl))amine is described in detail. The characterized complexes with ...Mn, Fe, Re and Ru as metal centers showed good activities regarding the reduction of several prochiral ketones. Comparing these catalysts, the non‐noble metal complexes produced best selectivities not only for aromatic substrates, but also for different kinds of aliphatic ones leading to enantioselectivities up to 99% ee. Theoretical investigations elucidated the mechanism and rationalized the selectivity.
Catalytic hydrogenation of carboxylic acid esters is essential for the green production of pharmaceuticals, fragrances, and fine chemicals. Herein, we report the efficient hydrogenation of esters ...with manganese catalysts based on simple bidentate aminophosphine ligands. Monoligated Mn PN complexes are particularly active for the conversion of esters into the corresponding alcohols at Mn concentrations as low as 0.2 mol % in the presence of sub‐stoichiometric amounts of KOtBu base.
It's SuperMn! A bidentate MnI P,N complex is a highly active catalyst for the hydrogenation of esters under mild conditions. Quantitative yields of alcohols are obtained for a variety of aliphatic and aromatic esters, while showing complete chemoselectivity for ester reduction in the presence of internal and terminal alkene functionalities.
The cover picture shows the opening of a new chapter in the field of pincer and pincer‐type complexes: “Manganese Pincer Complexes”. After ruthenium, iridium, and iron‐based pincer‐type complexes ...have been established as state‐of‐the‐art catalysts for (de)hydrogenation reactions in the past decade, manganese pincer complexes have most recently been successfully applied in related transformations. Details on their recent progress in (de)hydrogenation and transfer (de)hydrogenation as well as in C–C and C–X bond‐forming reactions are presented in the Microreview by M. Beller et al. on page 4344 ff (https://doi.org/10.1002/ejoc.201700376).
Cyclophilins (CYPs) are a group of ubiquitous prolyl cis/trans isomerases (PPIases). It was shown that plants possess the most diverse CYP families and that these are abundant in the phloem ...long-distance translocation stream. Since phloem exudate showed PPIase activity, three single-domain CYPs that occur in phloem samples from Brassica napus were characterised on functional and structural levels. It could be shown that they exhibit isomerase activity and that this activity is controlled by a redox regulation mechanism, which has been postulated for divergent CYPs. The structure determination by small-angle X-ray scattering experiments revealed a conserved globular shape. In addition, the high-resolution crystal structure of BnCYP19-1 was resolved and refined to 2.0 Å resolution, and the active sites of related CYPs as well as substrate binding were modelled. The obtained data and results support the hypothesis that single domain phloem CYPs are active phloem PPIases that may function as chaperones.
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