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.
Among the known liquid organic hydrogen carriers, formic acid attracts increasing interest in the context of safe and reversible storage of hydrogen. Here, the first molecularly defined cobalt pincer ...complex is disclosed for the dehydrogenation of formic acid in aqueous medium under mild conditions. Crucial for catalytic activity is the use of the specific complex 3. Compared to related ruthenium and manganese complexes 7 and 8, this optimal cobalt complex showed improved performance. DFT computations support an innocent non‐classical bifunctional outer‐sphere mechanism on the triplet state potential energy surface.
Co catalysis: The first molecularly defined cobalt pincer complex is disclosed for the dehydrogenation of formic acid in aqueous medium under mild conditions. Crucial to success is the use of a PNP pincer dentate CoI complex.
Abstract
Due to the complexity of heterogeneous catalysts, identification of active sites and the ways for their experimental design are not inherently straightforward but important for tailored ...catalyst preparation. The present study reveals the active sites for efficient C–H bond activation in C
1
–C
4
alkanes over ZrO
2
free of any metals or metal oxides usually catalysing this reaction. Quantum chemical calculations suggest that two Zr cations located at an oxygen vacancy are responsible for the homolytic C–H bond dissociation. This pathway differs from that reported for other metal oxides used for alkane activation, where metal cation and neighbouring lattice oxygen form the active site. The concentration of anion vacancies in ZrO
2
can be controlled through adjusting the crystallite size. Accordingly designed ZrO
2
shows industrially relevant activity and durability in non-oxidative propane dehydrogenation and performs superior to state-of-the-art catalysts possessing Pt, CrO
x
, GaO
x
or VO
x
species.
A general and atom‐economical synthesis of 1,1‐diborylalkanes from alkenes and a borane without the need for an additional H2 acceptor is reported for the first time. The key to our success is the ...use of an earth‐abundant zirconium‐based catalyst, which allows a balance of self‐contradictory reactivities (dehydrogenative boration and hydroboration) to be achieved. Our method avoids using an excess amount of another alkene as an H2 acceptor, which was required in other reported systems. Furthermore, substrates such as simple long‐chain aliphatic alkenes that did not react before also underwent 1,1‐diboration in our system. Significantly, the unprecedented 1,1‐diboration of internal alkenes enabled the preparation of 1,1‐diborylalkanes.
An earth‐abundant zirconium‐based catalyst has been developed for the selective 1,1‐diboration of bulk and inexpensive alkenes with a borane without the need for an additional H2 acceptor. Many aryl alkenes as well as long‐chain aliphatic alkenes convert smoothly into their corresponding 1,1‐diborylalkanes and the method also allows the unprecedented remote 1,1‐diboration of internal alkenes.
A selection of cobalt(I) and cobalt(II) pincer type complexes with different substitution patterns was tested in the catalytic reduction of carboxylic acid esters to alcohols. The cobalt pincer type ...complex 4 is suitable for the hydrogenation of aromatic as well as aliphatic and cyclic esters. Mechanistic investigation indicated a metal ligand cooperated reaction pathway.
An efficient cobalt PNP pincer type catalyst has been developed for the catalytic reduction of carboxylic acid esters to alcohols. The cobalt pincer type complex was made that is suitable for the hydrogenation of numerous aromatic as well as aliphatic and cyclic esters. Mechanistic investigation indicated a metal ligand cooperated reaction pathway.
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.
Generally, a homogeneous catalyst exhibits good activity and defined active sites but it is difficult to recycle. Meanwhile, a heterogeneous catalyst can easily be reused but its active site is ...difficult to reveal. It is interesting to bridge the gap between homogeneous and heterogeneous catalysis via controllable construction of a heterogeneous catalyst containing defined active sites. Here, we report that a molecularly defined, single-active site heterogeneous catalyst has been designed and prepared via the oxidative polymerization of maleimide derivatives. These polymaleimide derivatives can be active catalysts for the selective oxidation of heterocyclic compounds to quinoline and indole via the recycling of -C=O and -C-OH groups, which was confirmed by tracing the reaction with GC-MS using maleimide as the catalyst and by FT-IR analysis with polymaleimide as the catalyst. These results might promote the development of heterogeneous catalysts with molecularly defined single active sites exhibiting a comparable activity to homogeneous catalysts.
Hydrogenation of esters to alcohols with a well‐defined iron iPr2PNP pincer complex has been recently reported by us and other groups. We now introduce a novel and sterically less hindered Et2PNP ...congener that provides superior catalytic activity in the hydrogenation of various carboxylic acid esters and lactones compared to the known complex. Successful hydrogenation proceeds under relatively mild conditions (60 °C) with lower catalyst loadings.
Selective cleavage and subsequent functionalization of C-C single bonds present a fundamental challenge in synthetic organic chemistry. Traditionally, the activation of C-C single bonds has been ...achieved using stoichiometric transition-metal complexes. Recently, examples of catalytic processes were developed in which use is made of precious metals. However, the use of inexpensive and Earth-abundant group IV metals for catalytic C-C single-bond cleavage is largely underdeveloped. Herein, the zirconium-catalyzed C-C single-bond cleavage and subsequent hydroboration reactions is realized using Cp
ZrCl
as a catalytic system. A series of structures of various γ-boronated amines are readily obtained, which are otherwise difficult to obtain. Mechanistic studies disclose the formation of a N-Zr
species, and then a β-carbon elimination route is responsible for C-C single bond activation. Besides zirconium, hafnium exhibits a similar performance for this transformation.
Selective catalytic reductions of nitriles are presented using the commercially available Ru‐Macho‐BH complex. A variety of aliphatic, aromatic and (hetero)cyclic nitriles including industrially ...important adipodinitrile are hydrogenated to the corresponding primary amines. Modelling suggests the reaction follows an outer sphere hydrogenation mechanism.
An efficient and selective catalytic reduction of nitriles is presented using the commercially available Ru‐Macho‐BH complex. A variety of aliphatic, aromatic and (hetero)cyclic nitriles including the industrially important adipodinitrile are hydrogenated to the corresponding primary amines. The reaction follows an outer‐sphere mechanism.
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