Search

A novel synthetic protocol for the direct oxidation of alkanes, including cyclic and linear ones, to give ketones and alcohols using hydrogen peroxide as terminal oxidant under ambient conditions is presented. The active catalyst for this challenging transformation is conveniently generated by combination of simple Fe salts with N‐methyl bis(picolylamine) (Me‐bpa). Utilizing picolinic acid as additive leads to improved yields of ketones and alcohols (32‐57 %). The reaction can be conveniently scaled up to multi‐g scale. [ABSTRACT FROM AUTHOR]

The use of bis(NHC) manganese(I) complexes 3 as catalysts for the hydrogenation of esters was investigated. For that purpose, a series of complexes has been synthesized via an improved two step procedure utilizing bis(NHC)‐BEt3 adducts. By applying complexes 3 with KHBEt3 as additive, various aromatic and aliphatic esters were hydrogenated successfully at mild temperatures and low catalyst loadings, highlighting the efficiency of the novel catalytic system. The versatility of the developed catalytic system was further demonstrated by the hydrogenation of other substrate classes like ketones, nitriles, N‐heteroarenes and alkenes. Mechanistic experiments and DFT calculations indicate an inner sphere mechanism with the loss of one CO ligand and reveal the role of BEt3 as cocatalyst. [ABSTRACT FROM AUTHOR]

The well‐defined iron PNP pincer complex catalyst [Fe(H)(BH4)(CO)(HN{CH2CH2P(iPr)2}2] was used for the catalytic dehydrogenation of secondary alcohols to give the corresponding ketones. Using acetone as inexpensive hydrogen acceptor enables the oxidation with good to excellent yields. DFT computations indicate an outer‐sphere mechanism and support the importance of an acceptor to achieve this transformation under milder conditions. [ABSTRACT FROM AUTHOR]

Non‐noble metal catalysts based on pincer type compounds are of special interest for organometallic chemistry and organic synthesis. Next to iron and manganese, currently cobalt–pincer type complexes are successfully applied in various catalytic reactions. In this review the recent progress in (de)hydrogenation, transfer hydrogenation, hydroboration and hydrosilylation as well as dehydrogenative coupling reactions using cobalt–pincer complexes is summarised. Feeling the pinch! In this review, we describe the recent progress of cobalt–pincer‐type catalysts. Besides their synthesis and general reactivity, specific catalytic applications are summarised including (de)hydrogenations, transfer (de)hydrogenations, hydroborations and hydrosilylation reactions. [ABSTRACT FROM AUTHOR]

Abstract: The first cobalt‐catalyzed hydrogenative N‐methylation and alkylation of amines with readily available carboxylic acid feedstocks as alkylating agents and H2 as ideal reductant is described. Combination of tailor‐made triphos ligands with cobalt(II) tetrafluoroborate significantly improved the efficiency, thus promoting the reaction under milder conditions. This novel protocol allows for a broad substrate scope with good functional group tolerance, even in the presence of reducible alkenes, esters, and amides. [ABSTRACT FROM AUTHOR]

Herein, a general and efficient method for the homogeneous cobalt-catalyzed hydrogenation of N-heterocycles, under mild reaction conditions, is reported. Key to success is the use of the tetradentate ligand tris(2-(diphenylphosphino)phenyl)phosphine). This non-noble metal catalyst system allows the selective hydrogenation of heteroarenes in the presence of a broad range of other sensitive reducible groups. [ABSTRACT FROM AUTHOR]

A general procedure for the catalytic hydrogenation of nitriles to primary amines by using a non-noble metal-based system is presented. Co(acac)3 in combination with tris[2-(dicyclohexylphosphino)ethyl]phosphine efficiently catalyzes the selective hydrogenation of a wide range of (hetero)aromatic and aliphatic nitriles to give the corresponding amines. [ABSTRACT FROM AUTHOR]

For the first time an easily accessible and well-defined manganese N, N, N-pincer complex catalyzes the transfer hydrogenation of a broad range of ketones with good to excellent yields. This cheap earth abundant-metal based catalyst provides access to useful secondary alcohols without the need of hydrogen gas. Preliminary investigations to explore the mechanism of this transformation are also reported. [ABSTRACT FROM AUTHOR]

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-PNP iPr catalyst, as a turnover of more than 20 000 was reached. In addition to methanol, other important hydrogen carriers were also successfully dehydrogenated. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Triglycerides are used for the direct N-alkylation of amines with molecular hydrogen for the first time. A broad range of interesting and industrially relevant secondary and tertiary amines are obtained in the presence of an in situ formed Ru/Triphos complex. Notably, plant oil can be efficiently applied in this single-step process. Moreover, a variety of other methyl esters can be used as N-alkylation agents in the presence of hydrogen for the synthesis of more advanced building blocks. [ABSTRACT FROM AUTHOR]

Reported herein, for the first time, is the selective ruthenium-catalyzed reductive alkoxylation and amination of phthalimides/succinimides. Notably, this novel methodology avoids hydrogenation of the aromatic ring and allows methoxylation of substituted imides with good to excellent selectivity for one of the carbonyl groups. The reported method opens the door to the development of new processes for the selective synthesis of various functionalized N-heterocyclic compounds. As an example, intramolecular reductive couplings to afford tricyclic compounds are presented for the first time. [ABSTRACT FROM AUTHOR]

The 'green' reduction of carboxylic acids to alcohols is a challenging task in organic chemistry. Herein, we describe a general protocol for generation of alcohols by catalytic hydrogenation of carboxylic acids. Key to success is the use of a combination of Ru(acac)3, triphos and Lewis acids. The novel method showed broad substrate tolerance and a variety of aliphatic carboxylic acids including biomass-derived compounds can be smoothly reduced. [ABSTRACT FROM AUTHOR]

Pincer complexes are becoming increasingly important for organometallic chemistry and organic synthesis. Since numerous applications for such catalysts have been developed in recent decades, this Minireview covers progress in their use as catalysts for (de)hydrogenation and transfer (de)hydrogenation reactions during the last four years. Aside from noble-metal-based pincer complexes, the corresponding base metal complexes are also highlighted and their applications summarized. [ABSTRACT FROM AUTHOR]

Ethers are of fundamental importance in organic chemistry and they are an integral part of valuable flavors, fragrances, and numerous bioactive compounds. In general, the reduction of esters constitutes the most straightforward preparation of ethers. Unfortunately, this transformation requires large amounts of metal hydrides. Presented herein is a bifunctional catalyst system, consisting of Ru/phosphine complex and aluminum triflate, which allows selective synthesis of ethers by hydrogenation of esters or carboxylic acids. Different lactones were reduced in good yields to the desired products. Even challenging aromatic and aliphatic esters were reduced to the desired products. Notably, the in situ formed catalyst can be reused several times without any significant loss of activity. [ABSTRACT FROM AUTHOR]

The first selective iridium-catalyzed hydrogenations of esters are presented. By using a commercially available iridium pincer complex more than 20 different aromatic, aliphatic, and (hetero)cyclic esters are reduced to the corresponding alcohols in moderate to very good yields. An outer-sphere mechanism is proposed on the basis of our computational analysis. [ABSTRACT FROM AUTHOR]

We present the first base-free Fe-catalyzed ester reduction applying molecular hydrogen. Without any additives, a variety of carboxylic acid esters and lactones were hydrogenated with high efficiency. Computations reveal an outer-sphere mechanism involving simultaneous hydrogen transfer from the iron center and the ligand. This assumption is supported by NMR experiments. [ABSTRACT FROM AUTHOR]

A general catalytic protocol for the methylation of amines has been developed applying, for the first time, formic acid as the C1 building block and silanes as reducing agents. A broad range of aromatic and aliphatic, both primary and secondary, amines has been converted to the corresponding tertiary amines including [ N-13C]-labelled drugs in good to excellent yields under mild conditions. [ABSTRACT FROM AUTHOR]

The platinum-catalyzed hydrosilylation of amides to afford amines selectively is reported. By using defined platinum/N-heterocyclic carbene complexes, the reduction of secondary and tertiary amines takes place under mild conditions. [ABSTRACT FROM AUTHOR]

The article discusses the importance of selective methylation of amines with carbon dioxide (CO2) and hydrogen (H2) in the construction of organic compounds in nature. It states the developments of thermodynamically stable carbon dioxide (CO2) molecules which formates into methanol and methane. It also emphasizes on the developments of efficient methylation methods which uses bioactive compounds to create chemicals.

Not a ‘B'ore! Benzothiophene‐based boronic acids catalyze the reduction of tertiary, secondary, and primary amides in the presence of a hydrosilane. The reaction demonstrates good functional‐group tolerance. [ABSTRACT FROM AUTHOR]

Committed carbenes: The convenient application of bidentate carbene ligands is described for the hydrogenation of carboxylic acid esters. The ligand precursors are easily synthesized through the dimerization of N‐substituted imidazoles with diiodomethane. The catalyst is generated in situ and exhibits good activity and functional group tolerance for the hydrogenation of aromatic and aliphatic carboxylic acid esters. [ABSTRACT FROM AUTHOR]

A novel catalytic system formed from Fe(stearate)2/NH2CH2CH2NH2 and polymethylhydrosiloxane was directly developed for the hydrosilylation of carboxylic acid esters to alcohols. The catalytic method exhibits broad substrate scope, including 20 aliphatic, aromatic, and heterocyclic esters. The corresponding alcohols are obtained in moderate to very good yields. [ABSTRACT FROM AUTHOR]

A family of iron complexes with general formula [Fe(II)(R,Y,XPyTACN)(CF3SO3)2], where R,Y,XPyTACN=1-[2′-(4-Y-6-X-pyridyl)methyl]-4,7-dialkyl-1,4,7-triazacyclononane, X and Y refer to the groups at positions 4 and 6 of the pyridine, respectively, and R refers to the alkyl substitution at N-4 and N-7 of the triazacyclononane ring, are shown to be catalysts for efficient and selective alkene oxidation (epoxidation and cis-dihydroxylation) employing hydrogen peroxide as oxidant. Complex [Fe(II)(Me,Me,HPyTACN)(CF3SO3)2] ( 7), was identified as the most efficient and selective cis-dihydroxylation catalyst among the family. The high activity of 7 allows the oxidation of alkenes to proceed rapidly (30 min) at room temperature and under conditions where the olefin is not used in large amounts but instead is the limiting reagent. In the presence of 3 mol% of 7, 2 equiv. of H2O2 as oxidant and 15 equiv. of water, in acetonitrile solution, alkenes are cis-dihydroxylated reaching yields that might be interesting for synthetic purposes. Competition experiments show that 7 exhibits preferential selectivity towards the oxidation of cis olefins over the trans analogues, and also affords better yields and high [ syn-diol]/[epoxide] ratios when cis olefins are oxidized. For aliphatic substrates, reaction yields attained with the present system compare favourably with state of the art Fe-catalyzed cis-dihydroxylation systems, and it can be regarded as an attractive complement to the iron and manganese systems described recently and which show optimum activity against electron-deficient and aromatic olefins. [ABSTRACT FROM AUTHOR]

The epoxidation of olefins with methyltrioxorhenium (MTO) in the presence of various chiral oxazolines and pyridinebis(oxazoline) ligands as well as achiral N-ligands has been investigated. By applying 1-octene as a model system, reaction conditions were optimized, and high yields and good chemoselectivity (>90 %) were achieved. By applying other aromatic and aliphatic olefins, similar chemoselectivities and up to 19 % enantioselectivity were obtained. [ABSTRACT FROM AUTHOR]

A novel catalyst system for efficient amination of allylic alcohols with aryl and alkyl amines is presented. By applying a convenient combination consisting of Pd(OAc)2/1,10-phenanthroline, a variety of allylic alcohols reacted smoothly to give the corresponding secondary and tertiary amines in good to excellent yields with high regioselectivity. The usefulness of our protocol is demonstrated in the one-step synthesis of the antifungal drug naftifine and the calcium channel blocker flunarizine. [ABSTRACT FROM AUTHOR]

Abstract: A novel defined iron catalyst for the epoxidation of aromatic and aliphatic olefins with hydrogen peroxide as the terminal oxidant is described. Our catalyst approach is based on bio-inspired both alkyl- and aryl-substituted imidazoles in combination with cheap and abundant iron trichloride hexahydrate. Heterocycles similar to imidazole can be used as ligands in this epoxidation system, too. The novel system is stable towards air and water. It is shown that the mechanism depends strongly on the used ligands and substrates. In the presence of radical scavengers no carbon-centered radical could be detected. [ABSTRACT FROM AUTHOR]

Highlights from the article: Keywords: homogeneous catalysis; iron; oxidation; pincer ligands; transfer dehydrogenation B The Front Cover b shows the transfer dehydrogenation of secondary alcohols with a well-defined iron-PNP-pincer complex. Homogeneous catalysis, iron, oxidation, pincer ligands, transfer dehydrogenation.

The cover page of the journal "Angewandte Chemie International Edition" is presented.

Abstract: Easily accessible in situ catalysts composed of [Ru(cod)(2-methylallyl)2] and N-heterocyclic carbene ligands have been developed for the environmentally benign hydrogenation of various nitriles to give primary amines. Applying optimized conditions in the presence of SIMesBF4 as ligand high catalyst activity of up to 392h−1 is achieved in the hydrogenation of benzonitrile. The general applicability and functional group tolerance of this novel catalyst system are shown in the reduction of ten different nitriles. [Copyright &y& Elsevier]

The article discusses the importance of selective methylation of amines with carbon dioxide (CO2) and hydrogen (H2) in the construction of organic compounds in nature. It states the developments of thermodynamically stable carbon dioxide (CO2) molecules which formates into methanol and methane. It also emphasizes on the developments of efficient methylation methods which uses bioactive compounds to create chemicals.

Abstract: Novel ruthenium carbene complexes have been in situ generated and tested for the transfer hydrogenation of ketones. Applying Ru(cod)(methylallyl)2 in the presence of imidazolium salts in 2-propanol and sodium-2-propanolate as base, turnover frequencies up to 346h−1 have been obtained for reduction of acetophenone. A comparative study involving ruthenium carbene and ruthenium phosphine complexes demonstrated the higher activity of ruthenium carbene complexes. [Copyright &y& Elsevier]