Non‐Heme‐Type Ruthenium Catalyzed Chemo‐ and Site‐Selective C−H Oxidation

Herein, we developed a Ru(II)(BPGA) complex that could be used to catalyze chemo‐ and site‐selective C?H oxidation. The described ruthenium complex was designed by replacing one pyridyl group on tris(2‐pyridylmethyl)amine with an electron‐donating amide ligand that was critical for promoting this type of reaction. More importantly, higher reactivities and better chemo‐, and site‐selectivities were observed for reactions using the cis‐ruthenium complex rather than the trans‐one. This reaction could be used to convert sterically less hindered methyne and/or methylene C?H bonds of a various organic substrates, including natural products, into valuable alcohol or ketone products.     

The Origin of the Selectivity and Activity of Ruthenium‐Cluster Catalysts for Fuel‐Cell Feed‐Gas Purification: A Gas‐Phase Approach

Gas‐phase ruthenium clusters Ru_n⁺ (n=2–6) are employed as model systems to discover the origin of the outstanding performance of supported sub‐nanometer ruthenium particles in the catalytic CO methanation reaction with relevance to the hydrogen feed‐gas purification for advanced fuel‐cell applications. Using ion‐trap mass spectrometry in conjunction with first‐principles density functional theory calculations three fundamental properties of these clusters are identified which determine the selectivity and catalytic activity: high reactivity toward CO in contrast to inertness in the reaction with CO₂; promotion of cooperatively enhanced H₂ coadsorption and dissociation on pre‐formed ruthenium carbonyl clusters, that is, no CO poisoning occurs; and the presence of Ru‐atom sites with a low number of metal–metal bonds, which are particularly active for H₂ coadsorption and activation. Furthermore, comprehensive theoretical investigations provide mechanistic insight into the CO methanation reaction and discover a reaction route involving the formation of a formyl‐type intermediate.     

Synthesis of Quinolines via a Metal‐Catalyzed Dehydrogenative N‐Heterocyclization

Efficient ruthenium‐, rhodium‐, palladium‐, copper‐ and iridium‐catalysed methodologies have been recently developed for the synthesis of quinolines by the reaction of 2‐aminobenzyl alcohols with carbonyl compounds (aldehydes and ketones) or the related alcohols. The reaction is assumed to proceed via a sequence involving initial metal‐catalysed oxidation of 2‐aminobenzyl alcohols to the related 2‐aminobenzaldehydes, followed by cross aldol reaction with a carbonyl compound under basic conditions to afford α,β‐unsaturated carbonyl compounds. These aldehydes or ketones can be also generated in situ via dehydrogenation of the related primary and secondary alcohols. In the final step cyclodehydration of the α,β‐unsaturated carbonyl compound intermediates gives quinolines. Good yields of quinolines were also obtained by reacting 2‐nitrobenzyl alcohols and secondary alcohols in the presence of a ruthenium catalyst. Finally, aniline derivatives afforded also a useful access to quinolines by the reaction with 1,3‐propanediol or 3‐amino‐1‐propanol, or in a three‐component reaction with benzyl alcohol and aliphatic alcohols.     

Polymer‐Bound,Amphiphilic Hoveyda‐Grubbs‐Type Catalyst for Ring‐Closing Metathesis in Water

Summary: We report on the synthesis of a new amphiphilic, polymer‐bound variant of the Hoveyda‐Grubbs catalyst via the coupling reaction of a carboxylic acid‐functionalized poly(2‐oxazoline) block copolymer with 2‐isopropoxy‐5‐hydroxystyrene and subsequent reaction of the resulting macroligand with a second generation Grubbs catalyst. For the benchmark, the substrate diethyl diallylmalonate was studied in the ring‐closing metathesis (RCM) reaction and a turn‐over number (TON) of up to 390 in water was achieved. To the best of our knowledge, this is the highest value for any aqueous RCM reaction to date. For the first time, recycling of a ruthenium initiator in an aqueous RCM reaction has been successful to some extent. In addition, the micellar conditions accelerate the conversion of the hydrophobic diene and at the same time stabilize the active alkylidene species, although competing decomposition of the catalyst in water still impairs the catalyst performance. Residual ruthenium content was determined to be below 1 ppm in the product suggesting a very low leaching of the polymeric catalyst system.

Simplified chemical structure of the amphiphilic, polymer‐bound Grubbs‐Hoveyda catalyst.     

Triazole‐Assisted Ruthenium‐Catalyzed CH Arylation of Aromatic Amides

Site‐selective ruthenium(II)‐catalyzed direct arylation of amides was achieved through C?H cleavages with modular auxiliaries, derived from easily accessible 1,2,3‐triazoles. The triazolyldimethylmethyl (TAM) bidentate directing group was prepared in a highly modular fashion through copper(I)‐catalyzed 1,3‐dipolar cycloaddition and allowed for ruthenium‐catalyzed C?H arylations on arenes and heteroarenes, as well as alkenes, by using easy‐to‐handle aryl bromides as the arylating reagents. The triazole‐assisted C?H activation strategy was found to be widely applicable, to occur under mild reaction conditions, and the catalytic system was tolerant of important electrophilic functionalities. Notably, the flexible triazole‐based auxiliary proved to be a more potent directing group for the optimized ruthenium(II)‐catalyzed direct arylations, compared with pyridyl‐substituted amides or substrates derived from 8‐aminoquinoline.     

Low‐Valent Ruthenium Induced Simultaneous Reduction of Nitro Group and C‐C Double Bond in Nitroolefin 1‐Phenyl‐2‐Nitropropene‐1

The reduction of 1‐phenyl‐2‐nitropropene‐1 ( 1 ) on using ruthenium complexes was studied in detail in order to correlate this method with those previously recorded in the literature for the hydrogenation of nitroolefins. A variety of products was isolated by varying the reaction temperature and solvent. Among them was 1‐phenyl‐2‐propylamine ( 4 ), completely reduced from the selective both double bond and nitro group. 1‐Phenyl‐2‐propanol ( 5 ) was observed due to reduction of phenylacetone at 125 °C in the presence of ruthenium catalyst. When reaction temperature was lower than 125 °C, by employing RuCl₂(PPh₃)₃ complex, 1‐phenyl‐2‐nitropropane ( 2 ) and phenylacetone ( 3 ) were obtained, respectively. Ru‐BINAP complexes were attempted to produce chiral amine from starting material 1‐phenyl‐2‐nitropropene‐1 ( 1 ).     

Ruthenium‐Catalyzed para‐Selective C−H Alkylation of Aniline Derivatives

The para ‐selective C−H alkylation of aniline derivatives furnished with a pyrimidine auxiliary is herein reported. This reaction is proposed to take place via an N−H‐activated cyclometalate formed in situ. Experimental and DFT mechanistic studies elucidate a dual role of the ruthenium catalyst. Here the ruthenium catalyst can undergo cyclometalation by N−H metalation (as opposed to C−H metalation in meta ‐selective processes) and form a redox active ruthenium species, to enable site‐selective radical addition at the para position.     

Light‐Induced Ruthenium‐Catalyzed Nitrene Transfer Reactions: A Photochemical Approach towards N‐Acyl Sulfimides and Sulfoximines

1,4,2‐Dioxazol‐5‐ones are five‐membered heterocycles known to decarboxylate under thermal or photochemical conditions, thus yielding N‐acyl nitrenes. Described herein is a light‐induced ruthenium‐catalyzed N‐acyl nitrene transfer to sulfides and sulfoxides by decarboxylation of 1,4,2‐dioxazol‐5‐ones at room temperature, thus providing direct access to N‐acyl sulfimides and sulfoximines under mild reaction conditions. In addition, a one‐pot sulfur imidation/oxidation sequence catalyzed by a single ruthenium complex is reported.     

Enzyme‐ and Ruthenium‐Catalyzed Enantioselective Transformation of α‐Allenic Alcohols into 2,3‐Dihydrofurans

An efficient one‐pot method for the enzyme‐ and ruthenium‐catalyzed enantioselective transformation of α‐allenic alcohols into 2,3‐dihydrofurans has been developed. The method involves an enzymatic kinetic resolution and a subsequent ruthenium‐catalyzed cycloisomerization, which provides 2,3‐dihydrofurans with excellent enantioselectivity (up to >99 % ee). A ruthenium carbene species was proposed as a key intermediate in the cycloisomerization.     

Ruthenium‐Catalyzed Multicomponent Reactions: Access to α‐Silyl‐β‐Hydroxy Vinylsilanes,Stereodefined 1,3‐Dienes,and Cyclohexenes

The synthesis of densly functionized α‐silyl‐β‐hydroxyl vinylsilanes via ruthenium‐catalyzed multicomponent reaction (MCR) is reported herein. Exceptionally high regio‐ and diastereoselectivity was achieved by employing an unprecedented hydrosilylation of bifunctional silyl‐propargyl boronates. The simple protocol, mild reaction conditions, and unique tolerability of this method make it a valuable tool for the synthesis of highly elaborated building blocks. The one‐pot synthesis of stereodefined olefins, the generation of a valuable cyclohexene building block through a four‐component MCR, and further functionalization in an abundance of diastereoselective reactions is disclosed herein.     

Design of Mononuclear Ruthenium Catalysts for Low‐Overpotential Water Oxidation

Water oxidation is a key reaction in natural photosynthesis and in many schemes for artificial photosynthesis. Inspired by energy challenges and the emerging understanding of photosystem II, the development of artificial molecular catalysts for water oxidation has become a highly active area of research in recent years. In this Focus Review, we describe recent achievements in the development of single‐site ruthenium catalysts for water oxidation with a particular focus on the overpotential of water oxidation. First, we introduce the general scheme to access the high‐valent ruthenium–oxo species, the key species of the water‐oxidation reaction. Next, the mechanisms of the O? O bond formation from the active ruthenium–oxo species are described. We then discuss strategies to decrease the onset potentials of the water‐oxidation reaction. We hope this Focus Review will contribute to the further development of efficient catalysts toward sustainable energy‐conversion systems.     

Synthesis and Evaluation of Ruthenium 2‐Alkyl‐6‐mercaptophenolate Catalysts for Olefin Metathesis

A series of ruthenium carbene catalysts containing 2‐sulfidophenolate bidentate ligand with an ortho‐substituent next to the oxygen atom were synthesized. The molecular structure of ruthenium carbene complex containing 2‐isopropyl‐6‐sulfidophenolate ligand was confirmed through single crystal X‐ray diffraction. An oxygen atom can be found in the opposite position of the N‐heterocyclic carbene (NHC) based on the steric hindrance and strong trans‐effects of the NHC ligand. The ruthenium carbene catalyst can catalyze ring‐opening metathesis polymerization (ROMP) reaction of norbornene with high activity and Z‐selectivity and cross metathesis (CM) reactions of terminal alkenes with (Z)‐but‐2‐ene‐1,4‐diol to give Z‐olefin products (Z/E ratios, 70:30–89:11) in low yields (13%–38%). When AlCl₃ was added into the CM reactions, yields (51%–88%) were considerably improved and process becomes highly selective for E‐olefin products (E/Z ratios, 79:21–96:4). Similar to other ruthenium carbene catalysts, these new complexes can tolerate different functional groups.     

Visible‐Light‐Enabled Ruthenium‐Catalyzed meta‐C−H Alkylation at Room Temperature

Visible‐light‐induced ruthenium catalysis has enabled remote C?H alkylations with excellent levels of position control under exceedingly mild conditions at room temperature. The metallaphotocatalysis occurred under exogenous‐photosensitizer‐free conditions and features an ample substrate scope. The robust nature of the photo‐induced mild meta‐C?H functionalization is reflected by the broad functional group tolerance, and the reaction can be carried out in an operationally simple manner, setting the stage for challenging secondary and tertiary meta‐C?H alkylations by ruthenaphotoredox catalysis.     

Facile Fabrication of Solid‐state Electrochemiluminescence Sensor via Non‐covalent π‐π Stacking and Covalent Bonding on Graphite Electrode

Herein, a facile and efficient method was developed for fabrication of solid‐state electrochemiluminescence (ECL) sensor via non‐covalent π‐π stacking and covalent bonding on the graphite electrode (GE) surface. The electrode was firstly modified with 1‐aminopyrene via π‐π stacking between GE surface and the pyrene moiety. Thereafter a stable and efficient solid‐state ECL sensor was fabricated by covalent immobilization of ruthenium(II) onto the GE surface via amidation reaction between the 1‐aminopyrene and bis(2,2′‐bipyridyl)(4‐methyl‐4′‐carboxypropyl‐2,2′‐bipyridyl) ruthenium(II) bishexafluorophosphate. The sensor has been investigated using tripropylamine and tetracycline as representative analytes, and low detection limits of 0.7 nM and 3.5 nM (S/N=3) were reached, respectively.     

Ruthenium‐Catalyzed O‐ to S‐Alkyl Migration: A Pseudoreversible Barton–McCombie Pathway

A practical ruthenium‐catalyzed O‐ to S‐alkyl migration affords structurally diverse thiooxazolidinones in excellent yields. Our studies suggest this catalytic transformation proceeds through a pseudoreversible radical pathway drawing mechanistic parallels to the classic Barton–McCombie reaction.     

Synthesis of N,N,N-4,4＂-Di-（4-methylphenyl）-2,2＇：6＇,2＂- terpyridine-N,N,N-tris（isothiocyanato） Ruthenium（Ⅱ） and Application to Colorimetric Hg^2＋ Sensor

A terpyridine derivative DPTP [di-（4-methylphenyl）-2,2＇：6＇,2＂-terpyridine] was conveniently synthesized from 2-bromopyridine via halogen-dance reaction, Kharash coupling and Stille coupling reaction. Then its corresponding ruthenium complex Ru-DPTP [N,N,N-4,4＇＇-di-（4-methy,phenyl）-2,2＇：6＇,2＂-terpyridine-N,N,N-tris（is,-thi,cyanat,）- ruthenium（H） ammonium] was obtained and fully characterized by IR, UV-Vis, ESI MS and elemental analysis. The MLCT absorption band of Ru-DPTP was blue-shifted from 570 to 500 nm upon addition of Hg^2＋. Among a series of surveyed metal ions, the complex showed a unique recognition to Hg^2＋, indicating that it can be used as a selective colorimetric sensor for Hg^2＋.     

Ruthenium‐Catalyzed Transfer‐Hydrogenative Cyclization of 1,6‐Diynes with Hantzsch 1,4‐Dihydropyridine as a H2 Surrogate

The transfer‐hydrogenative cyclization of 1,6‐diynes with Hantzsch 1,4‐dihydropyridine as a H₂ surrogate was performed in the presence of a cationic ruthenium catalyst of the type [Cp′Ru(MeCN)₃PF₆]. Exocyclic 1,3‐dienes or their 1,4‐hydrogenation products, cycloalkenes, were selectively obtained, depending on the substrate structure and the reaction conditions.     

Double‐Stranded RNA‐Specific Templated Reaction with Triplex Forming PNA

RNA, originally perceived as a simple information transfer biopolymer, is emerging as an important regulator in cellular processes. A number of non‐coding RNAs are double‐stranded and there is a need for technologies to reliably detect and image such RNAs for biological and biomedical research. Herein we report double‐stranded RNA‐specific templated reaction resulting from PNA‐reagent conjugates that are brought within reactive distance through the formation of sequence‐specific triplexes onto double‐stranded RNA. The reaction makes use of a ruthenium‐based photocatalyst that reduces a pyridinium‐based immolative linker, unmasking a profluorophore. The reaction was shown to proceed with signal amplification and to be selective for double‐stranded RNA over DNA as well as single‐stranded RNA. The generality of the triplex formation was enabled by non‐canonical nucleobases that extend the Hoogsteen base‐pairing repertoire. The technology was applied to a templated reaction using pre‐microRNA 31.     

Domino N‐/C‐Arylation via In Situ Generation of a Directing Group: Atom‐Efficient Arylation Using Diaryliodonium Salts

Both aryl components of diaryliodonium salts can be used in a domino one‐pot reaction via in situ generation of a directing group. A number of heterocycles undergo N‐arylation which is followed by ruthenium‐catalyzed C‐arylation. Notably the reaction extends well to unsymmetrical diaryliodonium salts with a number of highly selective examples shown.     

Ruthenium‐catalyzed synthesis of quinolines via reductive heteroannulation of nitroarenes with 3‐amino‐1‐propanols

Nitroarenes are reductively cyclized with 3‐amino‐1‐propanols in dioxane/H₂O in the presence of a ruthenium catalyst and tin(II) chloride dihydrate together with isopropanol to afford the corresponding quinolines. A reaction pathway involving initial reduction of nitroarenes to anilines, propanol group transfer from 3‐amino‐1‐propanols to anilines, N‐alkylation of anilines by 3‐anilino‐1‐propanols and heteroannulation of 1,3‐dianilinopropanes is proposed.