Search

The novel reaction conditions allow the direct mono-N-alkylation of primary aromatic amines.

The ruthenium(II)-catalyzed hydration of terminal alkynes in PEG-400 to yield methyl ketones through Markovnikov addition of water across alkyne is reported.

Oxidation reactions are significant transformations used extensively in chemical production. Use of molecular oxygen as an oxidant is certainly environmental friendly and adds to the greenness of the process. A number of metal catalysts have been developed for aerobic oxidation. This digest summarizes the recent advances in aerobic oxidation reactions using ruthenium catalysts for various transformations such as C-H activation/cyclization, alkyne/alkene oxidation, and oxidation of alcohols and amines. (C) 2016 Elsevier Ltd. All rights reserved.

New pincer ruthenium complexes bearing a monodentate N-heterocyclic carbene ligand were synthesized and demonstrated as powerful hydrogenation catalysts. With an atmospheric pressure of hydrogen gas, aromatic, heteroaromatic, and aliphatic esters as well as lactones were converted into the corresponding alcohols at 50 °C. This reaction protocol offers reliable access to alcohols using an easy operational setup.

In this perspective, we have surveyed the synthetic procedure, characteristics, and reactivity of high-valent ruthenium–oxo complexes. The ruthenium–oxo complexes have served as ideal species to elucidate the characteristics of metal–oxo complexes in terms of not only geometrical and electronic structures but also oxidation reactivity and mechanisms of oxidation reactions. Due to the high stability and excellent reversibility of redox processes, ruthenium–oxo complexes have provided significant mechanistic insights into the oxidation of organic compounds including alcohols, alkenes, and alkanes and also water on the basis of detailed kinetic analysis.

A highly regioselective ruthenium-catalyzed C–H amidation of cyclic N-sulfonyl ketimines with organic sulfonyl azides is described. An alkenylation at the C–H bond of cyclic N-sulfonyl ketimines with various alkenes was also carried out. Only a catalytic amount of the oxidant Cu(OAc)2 was used in the reaction; the remainder of the required amount of oxidant was formed by regeneration of Cu(OAc)2 under an air atmosphere.

Substituted aromatic amides reacted efficiently with allylic acetates in the presence of a cationic ruthenium complex in ClCH2CH2Cl at room temperature providing ortho allylated benzamides in a highly regioselective manner without any oxidant and base. The whole catalytic reaction occurred in a Ru(II) oxidation state and thus the oxidation step is avoided. By tuning the reaction temperature, ortho allyl and vinyl benzamides were prepared exclusively. Later, ortho allyl and vinylated benzamides were converted into biologically useful six- and five-membered benzolactones in the presence of HCl.

Versatile ruthenium(II) complexes derived from amino acids enabled the first general C–H arylations of aryltetrazoles with inexpensive aryl chlorides. The user-friendly Piv-Val-OH-based ruthenium(II) catalyst was characterized by a broad substrate scope, excellent functional group tolerance, and high catalytic activity. Thereby, the ruthenium(II) catalysis set the stage for the step-economical preparation of the blockbuster antihypertension drug Valsartan, while displaying unique robustness in the C–H arylation regime.

The enhanced catalytic activity of ruthenium complex-bound norvaline Boc-L-[Ru]Nva-OMe 1, in which the ONO-pincer ruthenium complex Ru(pydc)(terpy) 2 is tethered to the α-side chain of norvaline, has been demonstrated for the oxidation of methoxybenzenes to p-benzoquinones with a wide scope of substrates and unique chemoselectivity.

This review provides a detailed overview about the synthesis, properties and applications of all ruthenium-fullerene compounds reported within the last 25 years. The incorporation of ruthenium centers into fullerene compounds by organometallic, covalent or non-covalent bonds has led to a broad range of useful hybrid materials. By this approach novel compounds could be generated that feature the electron-donating and electron-accepting character of ruthenium complexes and fullerenes, respectively. Intramolecular interactions between both units could result in new, combined properties that were studied in the spotlight of emerging applications, such as photovoltaics or catalysis.

CNN pincer ruthenium(II) and osmium(II) complexes of general formula RuCl(CNN)(dppb) (1 a-c) and OsCl(CNN)(dppb) (2 a,b) (dppb=Ph2P(CH2)4PPh2, HCNN=[6-(p-tolyl)-2-pyridyl]methylamine (4), N-methyl-[6-(p-tolyl)-2-pyridyl]methylamine (7) and N,N-dimethyl-[6-(p-tolyl)-2-pyridyl]methylamine (8)) were prepared and assessed as catalysts in the hydrogenation of a variety of imines. Among the examined complexes, the Ru-complex 1 a, RuCl(4)(dppb), showed the best activity, reducing N-aryl and N-alkyl imines to the related amines in high yields (up to 100 %) with a catalyst loading of 0.1-1 mol% and under mild conditions (5 atm H2, 40-70 °C). The Os-complexes exhibited a lower activity than their ruthenium analogues. Despite this, the Os-complex 2 a, OsCl(4)(dppb), was successful in the reduction of N-benzylideneaniline at 70 °C, affording a rare example of application of osmium complexes in the catalytic hydrogenation of imines.

Synthesis of 2-(2H-1,2,3-triazole-2-yl)aniline derivatives from 2-aryl-1,2,3-triazoles and sulfonylazides through ruthenium-catalyzed intermolecular C–H amidation is achieved. This reaction provides an environmentally benign protocol for C–N bond formation, producing N2 gas as the sole byproduct. Yet a number of functionalities are well tolerated, obtaining the desired products in moderate to excellent yields.

A versatile method for the Ru(0)-catalyzed hydroarylation of alkynes using weakly-coordinating ketones enabled by the in situ generation of a Ru(0) catalyst from an air-stable, inexpensive and user-friendly Ru(II) precatalyst is reported for the first time. The method provides straightforward access to a wide range of functionalized ketone building blocks that would be difficult to access by conventional methods. Most crucially, this report demonstrates for the first time that the in situ generated Ru(0) catalysts advance the classic Ru(0)-catalyzed C–H functionalization platform to substrates that would otherwise be unreactive. Product manipulation and mechanistic studies are reported.

Some heterocyclic substrates, substituted at the ortho-position of a heteroatom with alkyl substituents bearing a site-selective methyl group, are successfully silylated with reagent (II).

ConspectusThe transition-metal-catalyzed asymmetric cyclopropanation of olefins with diazoacetates has become one of the most important methods for the synthesis of optically active cyclopropane derivatives, which are key pharmaceutical building blocks and present in a large number of natural products. To date, significant progress has been made in this area of research, and efficient stereocontrolled synthetic approaches to cyclopropane derivatives have been developed using rhodium, ruthenium, copper, and cobalt catalysts. However, the vast majority of these strategies are limited to electron-rich olefins, such as styrene derivatives, due to the electrophilicity of the metal–carbene intermediates generated from the reaction of the metal with the diazo compound. Recently, the D2-symmetric Co(II)–phophyrin complexes developed by Zhang et al. were shown to be the most efficient catalysts for the asymmetric cyclopropanation of electron-deficient olefins. This catalytic system is mechanistically distinct from...

A ruthenium pincer catalyst has been shown to be highly effective for the hydrogenation of a wide range of α-keto esters, affording either diols or hydroxy esters depending on the choice of reaction conditions. Strong base, high temperature, and pressure favor the formation of diols whilst the opposite is true for the hydroxy esters.

Simple ruthenium precursor [Ru(p-cymene)Cl2]2 1 catalyzed regioselective 1,4-dearomatization of pyridine derivatives using pinacolborane is reported. Two catalytic intermediates, [Ru(p-cymene)Cl2Py] 2 and [Ru(p-cymene)Cl2(P(Cy)3)] 3, involved in this process are identified, independently synthesized, characterized, and further used directly as effective catalysts; two more catalytic intermediates [Ru(p-cymene)Cl2(Py)(P(Cy)3)] 4 and [Ru(p-cymene)(H)Cl(Py)(P(Cy)3)] 5 are identified in solution. Complex 5 is the active catalytic intermediate. An intramolecular selective 1,5-hydride transfer in 5 leading to the regioselective 1,4-hydroboration of pyridine compounds is proposed.

New bipyridinemethanamine-containing tetradentate ligands and their corresponding ruthenium complexes have been synthesized. The synthesized complexes performed well in the hydrogenation of a variety of esters with high efficiency (TON up to 9700) giving alcohols in good yields.

Over the past decade, significant advances have been made in the development of molecular water oxidation catalysts (WOCs) in the context of developing a system that would accomplish artificial photosynthesis. Mononuclear ruthenium complexes with polypyridine ligands have drawn considerable attention in this regard, due to their high catalytic activity and relatively simple structure. In this perspective review, we will discuss mononuclear Ru polypyridine WOCs by organizing them into four groups according to their ligand environments. Each group will be discussed with regard to three fundamental questions: first, how does the catalyst initiate O-O bond formation? Second, which step in the catalytic cycle is rate-determining? Third, how efficient is the catalyst according to the specific descriptors such as turnover frequency? All discussion is based on the high-valent ruthenium intermediates that are proposed in the catalytic cycle according to experimental observation and theoretical simulation. Two fundamental mechanisms are set forth. An acid-base mechanism that involves the attack of a water molecule on the oxo of a high valent Ru 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 O species to form the O-O bond. Subsequent steps lead to dissociation of O2 and rehydration of the metal center. A second mechanism involves the formation of a Ru-O˙ radical species, two of which then couple to form a Ru-O-O-Ru species that can release O2 afterwards. The acid-base mechanism appears to be more common and mechanistic differences could result from variation directly related to polypyridine ligand structures. Understanding how electronic, steric, and conformational properties can effect catalyst performance will lead to the rational design of more effective WOCs with not only ruthenium but also other transition metals.

An efficient C–H activation method for the ortho alkynylation of aromatic N-methoxyamides with hypervalent iodine–alkyne reagent using a ruthenium catalyst is described. The reaction proceeds under mild reaction conditions with broad substrate scope. A possible catalytic cycle involving a ruthenium carboxylate assisted C–H bond cleavage is proposed from the preliminary mechanistic evidence.

A plethora of strategies for immobilizing well-defined metathesis catalysts on solid supports have been developed over the past decades. Whereas most reviews on classical heterogeneous metathesis catalyst designs mainly discuss covalent binding approaches, we here extended this topic with non-covalent surface science methods, a research area that gained interest recently. Within this context, the main focus was set on the immobilization of ruthenium alkylidenes or so-called Grubbs complexes, as these catalysts are known for their high activity, stability and commercial viability. Besides giving an overview of different immobilization strategies, the wide diversity of supported Grubbs catalysts also allows for discussing implications of attaching Grubbs catalysts that go beyond the traditional benefits of heterogeneous catalysis, such as easy catalyst separation. More specifically, this Review will summarize several unique opportunities of immobilized homogeneous catalysts in liquid-phase metathesis transformations in terms of impact on activity, stability, and product selectivity, as to highlight the economic potential, but without ignoring possible shortcomings and limitations.

The incorporation of organometallic catalyst precursors in proteins results in so-called artificial metalloenzymes. The protein structure will control activity, selectivity and stability of the organometallic site in aqueous medium and allow non-natural reactions in biological settings. Grubbs-Hoveyda type ruthenium catalysts with an N-heterocyclic carbene (NHC) as ancillary ligand, known to be active in olefin metathesis, have recently been incorporated in various proteins. An overview of these artificial metalloproteins and their potential application in olefin metathesis is given.

The ruthenium-catalyzed redox isomerization of allylic alcohols was successfully coupled with the enantioselective enzymatic ketone reduction (mediated by KREDs) in a concurrent process in aqueous medium. The overall transformation, formally the asymmetric reduction of allylic alcohols, took place with excellent conversions and enantioselectivities, under mild reaction conditions, employing commercially and readily available catalytic systems, and without external coenzymes or cofactors. Optimization resulted in a multistep approach and a genuine cascade reaction where the metal catalyst and biocatalyst coexist from the beginning.

Synthesis of new air stable octahedral ruthenium(II) carbonyl complex bearing O, and N-bidentate benzhydrazone ligand is reported. It has been characterized by elemental analysis, spectral methods and single crystal X-ray diffraction method. The new catalyst has been effectively applied to the transfer hydrogenation reaction of various ketones using isopropanol as a solvent and KOH as a base at 82 °C and the maximum conversion is achieved up to 100%.

An atom-economical and environmentally friendly method to transform amino alcohols to amino acid salts using just basic water, without the need of pre-protection or added oxidant, catalyzed by a ruthenium pincer complex, is developed. Water is the solvent, the source of the oxygen atom of the carboxylic acid group, and the actual oxidant, with liberation of dihydrogen. Many important and useful natural and unnatural amino acid salts can be produced in excellent yields by applying this new method.

The first reverse regioselective intermolecular annulation of aryl substituted 2-acetylenic ketones with O-substituted N-hydroxybenzamides or acrylamides followed by tandem cyclization via ruthenium-catalyzed C–H activation, is reported. Excellent reverse selectivity of alkyne insertion was induced by the weak coordination between the carbonyl group and ruthenium complex. This highly efficient and practical reaction has a broad range of substrate scope with excellent functional-group tolerance. The tandem reaction provides a wide range of polycyclic products that have an indozilidine structural motif, and are found to potentially be synthetically and pharmaceutically valuable.

Topochemical reduction of the ordered double perovskite LaSrNiRuO6 with CaH2 yields LaSrNiRuO4, an extended oxide phase containing infinite sheets of apex-linked, square-planar Ni1+O4 and Ru2+O4 units ordered in a checkerboard arrangement. At room temperature the localized Ni1+ (d9, S = 1/2) and Ru2+ (d6, S = 1) centers behave paramagnetically. However, on cooling below 250 K the system undergoes a cooperative phase transition in which the nickel spins align ferromagnetically, while the ruthenium cations appear to undergo a change in spin configuration to a diamagnetic spin state. Features of the low-temperature crystal structure suggest a symmetry lowering Jahn–Teller distortion could be responsible for the observed diamagnetism of the ruthenium centers.

The catalytic conversion of alcohols into carboxylic acid salts in water was performed in the presence of ruthenium complexes supported by aliphatic PNP pincer ligands preformed or formed in situ. High activity toward a wide substrate scope was achieved with turnover number values of up to 4000. The air-stable catalytic system can be recycled by using toluene as a catalyst-immobilizing phase; the activity is maintained after five consecutive runs. Finally, mechanistic studies allowed some fundamental aspects related to water activation to be unveiled and to the mechanism postulated.

The ruthenium complex [(η6-cymene)Ru(Cl)(dpmpy)]+ {dpmpy = 2-[2-(dimethylamino)pyrimidin-4-yl]pyridine} is highly reactive in catalyzing the reductive amination of aromatic aldehydes through in situ generated imines with 2-propanol as the hydrogen source following a transfer-hydrogenation mechanism. This transformation does not require any activating additives and is applicable to a broad variety of aldehydes.

Catalytic cyclization reactions and new stoichiometric skeletal rearrangement cycloisomerizations of 2-ethynylphenyl vinyl ethers containing methyl substituents on the vinyl groups by using [Ru]Cl {[Ru]=Cp(PPh3)2Ru, Cp=η5-cyclopentadienyl} were observed in MeOH and CH2Cl2, respectively. In MeOH, the catalytic cyclization of three different enynes gave the corresponding benzoxepine derivatives in high yields in each case. Interestingly, in the stoichiometric reactions of [Ru]Cl with enynes, two unprecedented rearrangements of enynes were observed in CH2Cl2. The presence of a methyl group in the vinyl unit plays a critical role in choosing one of the double bonds of the vinylidene ligand, that is, the Ru=Cα or the Cα=Cβ bond, for the [2+2] cycloaddition in the cycloisomerization processes. Structure determination by single-crystal X-ray diffraction analysis along with various isotope studies corroborated the proposed mechanisms.

Methyl phenyl sulfoximine is used as a directing group in the ruthenium-catalyzed intramolecular hydroarylation of alkene-tethered benzoic acid derivatives to afford dihydrobenzofurans and indolines.

Two thermally activated ruthenium(ii) polypyridyl complexes, cis-Ru(bpy)2Cl2 and trans-Ru(qpy)Cl2 were investigated to determine the impact of the geometric arrangement of the exchangable ligands on the potential of the compounds to act as chemotherapeutics. In contrast to the geometry requirements for cisplatin, trans-Ru(qpy)Cl2 was 7.1-9.5× more cytotoxic than cis-Ru(bpy)2Cl2. This discovery could open up a new area of metal-based chemotherapeutic research.

This paper summarizes our recent progress on the preparations and applications of electropolymerized thin films of redox-active ruthenium complexes. Thin films of vinyl-functionalized diruthenium or ruthenium-amine conjugated complexes are prepared by reductive electropolymerization. The resulting films are useful for multistate near-infrared electrochromism, ion sensing, and mimicking flip-flop and flip-flap-flop logic gates. The oxidative electropolymerization of diruthenium complexes with two distal triarylamine units affords electropolymers with an alternating diruthenium and tetraphenylbenzidine structural unit. The applications of the resulting films in multistate near-infrared electrochromism and resistive memory are discussed.

A tandem olefin metathesis/oxidative cyclization has been developed to synthesize 2,5-disubstituted tetrahydrofuran (THF) diols in a stereocontrolled fashion from simple olefin precursors. The ruthenium metathesis catalyst is converted into an oxidation catalyst in the second step and is thus responsible for both catalytic steps. The stereochemistry of the 1,5-diene intermediate can be controlled through the choice of catalyst and the type of metathesis conducted. This olefin stereochemistry then controls the THF diol stereochemistry through a highly stereospecific oxidative cyclization.

A new benzylation protocol, enabling straightforward access to β-benzylated quinolines, has been demonstrated. By employing readily available [RuCl2(p-cymene)]2 as a catalyst and O2 as a sole green oxidant, various 1,2,3,4-tetrahydroquinolines were efficiently converted in combination with aryl aldehydes into desired products in a step- and atom-economic fashion together with the advantages of excellent functional group tolerance and chemoselectivity, offering an important basis for the transformation of saturated N-heterocycles into functionalized N-heteroaromatics via a dehydrogenative cross-coupling strategy. Mechanistic investigations support that the reaction undergoes a monodehydrogenation-triggered β-benzylation mode.

In the past decade, numerous examples of chemical technologies based on olefin metathesis have been developed to make olefin metathesis increasingly dominant in several sustainable and green chemical processes. In spite of the wide application profile, conjugated olefin metathesis, especially conjugated polyene metathesis, is an area of great interest with little exploration. The metathesis of conjugated polyenes is often cumbersome and requires a high catalyst loading, most probably because of the formation of poorly active or inactive ruthenium η3-vinylcarbene intermediates. A mechanistic understanding and the development of a new highly active catalytic system for olefin metathesis will open new areas for exploration, such as the utilisation of cyclopentadiene and other petrochemical by-products or a new way to use butadiene, isoprene and conjugated electron systems that contain natural products such as terpenes and polyunsaturated fatty acids. An understanding of the mechanism of ruthenium η1–η3-vinylcarbene interconversion may open the way to the development of a new generation of Ru-based latent metathesis catalyst systems. This review summarises the most relevant pioneering work focused on the metathesis of conjugated polyenes to open new ideas for the development of forthcoming latent metathesis catalysts and to explore different applications.

Asymmetric hydrogenation of various α-substituted acrylic acids was carried out using RuPHOX–Ru as a chiral catalyst under 5 bar H2, affording the corresponding chiral α-substituted propanic acids in up to 99% yield and 99.9% ee. The reaction could be performed on a gram-scale with a relatively low catalyst loading (up to 5000 S/C), and the resulting product (97%, 99.3% ee) can be used as a key intermediate to construct bioactive chiral molecules. The asymmetric protocol was successfully applied to an asymmetric synthesis of dihydroartemisinic acid, a key intermediate required for the industrial synthesis of the antimalarial drug artemisinin.

The DNA photoswitch [Ru(bpy)2dppz]2+ (bpy = 2,2′-bipyridine, dppz = dipyrido[3,2-a:2′,3′-c]phenazine) has attracted much attention and become a powerful tool for studying the interaction of metal polypyridyl complexes with DNA. A large number of Ru-dppz complexes have been designed for a wide range of uses in many fields. In this perspective, we first introduce the latest results of Ru-dppz complexes that bind with DNA. The mechanisms of the light-switch effect and the structural modifications of Ru-dppz systems are also briefly introduced. We also review the recent advances in biological applications of the Ru-dppz system in DNA binders, cellular imaging, anticancer drugs, protein aggregation detection and chemosensors.

The chiral ruthenium complex formed in situ from (TFA)2Ru(CO)(PPh3)2 and (R)-BINAP is found to catalyze the enantioselective C–C coupling of diverse primary alcohols with the 1,3-enyne, TMSC≡CC(Me)═CH2, to form secondary homopropargyl alcohols bearing gem-dimethyl groups. All reagents for this byproduct-free coupling are inexpensive and commercially available, making this protocol a practical alternative to stoichiometric carbanions in enantioselective carbonyl reverse prenylation.

Ruthenium(II) bis(carboxylate)s proved highly effective for two decarboxylative C−H alkenylation strategies. The decarboxylation proceeded efficiently at rather low temperatures. The unique versatility of the decarboxylative ruthenium(II) catalysis is reflected in the oxidative olefinations with alkenes as well as the redox-neutral hydroarylations of alkynes.

A method for the arylative coupling of alkynols or alkynyl hydroperoxides using equimolar amounts of diazonium salts at room temperature has been achieved through application of a gold/photoredox dual catalytic system. The excess of external reagents (oxidant or base) and high temperatures required by previous arylative Meyer-Schuster rearrangement protocols are avoided by exploitation of a visible light-mediated process.

The new thiazolinecarboxylate ruthenium complexes RUC and RUP show good catalytic activity in transfer hydrogenation reactions of a wide variety of carbonyl compounds.