Ruthenium Carboxylate Research Articles

Efficient, Facile, and Green Synthesis of Ruthenium Carboxylate Complexes by Manual Grinding

Recently, scientists have been developing sustainable processes, and in this context, mechanochemistry is commonly associated with green chemistry for its ability to reduce waste generation from chemical reactions. The well-known acetate complex, diacetate bis(triphenylphosphine) ruthenium(II) [Ru(OAc)2(PPh3)2], is a versatile precursor for preparing active complexes for several catalytic reactions. This report presents an efficient and straightforward manual grinding protocol for the sustainable synthesis of ruthenium carboxylate complexes starting from the commercially available [RuCl2(PPh3)3] and metal carboxylates. This work represents a novel and preliminary investigation into carboxylate precursors’ alternative solventless synthesis route based on manual grinding. To our knowledge, this is the first time [Ru(OAc)2(PPh3)2] has been prepared via a mechanochemical procedure. The synthesis method has also been investigated for other alkali metal carboxylates and yields ranging from 30 to 80% were obtained. A comparison of sustainability and environmental impact between conventional solution synthesis and the grinding route has been carried out using the E-factor and Mass Productivity. While for the acetate complex E-factor and MP were only slightly better compared with the solvent method (3 vs. 4 for E-factor and ~6 vs. 5 for MP), for benzoate higher results were found (1 vs. ~4 for E-factor and 10 vs. 5 for MP).

π-Extended Polyaromatic Hydrocarbons by Sustainable Alkyne Annulations through Double C-H/N-H Activation.

The widespread applications of substituted diketopyrrolopyrroles (DPPs) call for the development of efficient methods for their modular assembly. Herein, we present a π‐expansion strategy for polyaromatic hydrocarbons (PAHs) by C−H activation in a sustainable fashion. Thus, twofold C−H/N‐H activations were accomplished by versatile ruthenium(II)carboxylate catalysis, providing step‐economical access to diversely decorated fluorogenic DPPs that was merged with late‐stage palladium‐catalyzed C−H arylation on the thus‐assembled DPP motif.

Late-stage peptide C\u2013H alkylation for bioorthogonal C\u2013H activation featuring solid phase peptide synthesis

Methods for the late-stage diversification of structurally complex peptides hold enormous potential for advances in drug discovery, agrochemistry and pharmaceutical industries. While C–H arylations emerged for peptide modifications, they are largely limited to highly reactive, expensive and/or toxic reagents, such as silver(I) salts, in superstoichiometric quantities. In sharp contrast, we herein establish the ruthenium(II)-catalyzed C–H alkylation on structurally complex peptides. The additive-free ruthenium(II)carboxylate C–H activation manifold is characterized by ample substrate scope, racemization-free conditions and the chemo-selective tolerance of otherwise reactive functional groups, such as electrophilic ketone, bromo, ester, amide and nitro substituents. Mechanistic studies by experiment and computation feature an acid-enabled C–H ruthenation, along with a notable protodemetalation step. The transformative peptide C–H activation regime sets the stage for peptide ligation in solution and proves viable in a bioorthogonal fashion for C–H alkylations on user-friendly supports by means of solid phase peptide syntheses.

Two-Dimensional Mixed-Metal Complexes Composed of Mixed-Valent Dinuclear Ruthenium(II,III) Carboxylate and Tetracyanidopalladate(II) Units

Two-Dimensional Mixed-Metal Complexes Composed of Mixed-Valent Dinuclear Ruthenium(II,III) Carboxylate and Tetracyanidopalladate(II) Units

Ruthenium(II)‐Catalyzed C–H Alkenylation of Quinones: Diversity‐Oriented Strategy for Trypanocidal Compounds

Ruthenium(II)‐catalysis enabled C–H alkenylations of unactivated naphthoquinones for the preparation of A‐ring‐modified naphthoquinoidal compounds with activity against Trypanosoma cruzi, the parasite causing Chagas disease. The present study encompasses C–H alkenylation by weak O‐coordination by means of ruthenium(II) carboxylates. This method provided an efficient and versatile tool towards a diversity‐oriented strategy for the preparation of compounds with a relevant biological profile.

Crystal Structure of Mixed-metal Complex of Paddle-wheel-type Dinuclear Ruthenium(II,III) Carboxylate and Tetracyanidopalladate(II)

The crystal structure of mixed-metal complex of ruthenium propionate and tetracyanidopalladate(II), [{Ru2(C2H5CO2)4}2Pd(CN)4]n, was determined by the single-crystal X-ray diffraction method at 90 K. It crystallizes in the triclinic space group P1 with a = 9.8123(16)Å, b = 11.961(2)Å, c = 17.645(3)Å, α = 90.007(3), β = 90.634(3), γ = 108.285(2)°, V = 1966.2(6)Å3, Dx = 2.026 g/cm3, and Z = 2. The R1 [I > 2σ(I)] and wR2 (all data) values are 0.0788 and 0.1499, respectively, for all 8847 independent reflections. In the crystal, paddle-wheel-type dinuclear ruthenium cores are connected by tetracyanidopalladate(II) ions in an alternate arrangement to form a two-dimensional sheet constructed of 28-membered [–Ru2–NC–Pd–CN–]4 rings.

Electrooxidative Ruthenium‐Catalyzed C−H/O−H Annulation by Weak O‐Coordination

AbstractElectrocatalysis has been identified as a powerful strategy for organometallic catalysis, and yet electrocatalytic C−H activation is restricted to strongly N‐coordinating directing groups. The first example of electrocatalytic C−H activation by weak O‐coordination is presented, in which a versatile ruthenium(II) carboxylate catalyst enables electrooxidative C−H/O−H functionalization for alkyne annulations in the absence of metal oxidants; thereby exploiting sustainable electricity as the sole oxidant. Mechanistic insights provide strong support for a facile organometallic C−H ruthenation and an effective electrochemical reoxidation of the key ruthenium(0) intermediate.

Electrooxidative Ruthenium-Catalyzed C-H/O-H Annulation by Weak O-Coordination.

Electrocatalysis has been identified as a powerful strategy for organometallic catalysis, and yet electrocatalytic C-H activation is restricted to strongly N-coordinating directing groups. The first example of electrocatalytic C-H activation by weak O-coordination is presented, in which a versatile ruthenium(II) carboxylate catalyst enables electrooxidative C-H/O-H functionalization for alkyne annulations in the absence of metal oxidants; thereby exploiting sustainable electricity as the sole oxidant. Mechanistic insights provide strong support for a facile organometallic C-H ruthenation and an effective electrochemical reoxidation of the key ruthenium(0) intermediate.

Quinazoline‐Directed C–H Bond Functionalization Catalyzed by Ruthenium(II) Carboxylate – Construction of Polyconjugated Aryl‐Heteroaryl Systems

A series of coupling products have been prepared by a ruthenium(II)‐catalyzed direct ortho‐C–H arylation of 2‐(aryl/heteroaryl)‐substituted quinazolines with (hetero)aryl bromides. Tri(hetero)aryl‐substituted alkenes were also prepared by olefinic C–H activation of 2‐(2‐arylvinyl)quinazoline derivatives. High conversions and selectivities were achieved by choosing the appropriate ruthenium(II) carboxylate catalyst system, solvent, and reaction temperature. The possibility of a C(sp3)–H functionalization by applying an arylation/reduction reaction sequence was also demonstrated.

Bioorthogonal Diversification of Peptides through Selective Ruthenium(II)‐Catalyzed C–H Activation

AbstractMethods for the chemoselective modification of amino acids and peptides are powerful techniques in biomolecular chemistry. Among other applications, they enable the total synthesis of artificial peptides. In recent years, significant momentum has been gained by exploiting palladium‐catalyzed cross‐coupling for peptide modification. Despite major advances, the prefunctionalization elements on the coupling partners translate into undesired byproduct formation and lengthy synthetic operations. In sharp contrast, we herein illustrate the unprecedented use of versatile ruthenium(II)carboxylate catalysis for the step‐economical late‐stage diversification of α‐ and β‐amino acids, as well as peptides, through chemo‐selective C−H arylation under racemization‐free reaction conditions. The ligand‐accelerated C−H activation strategy proved water‐tolerant and set the stage for direct fluorescence labelling as well as various modes of peptide ligation with excellent levels of positional selectivity in a bioorthogonal fashion. The synthetic utility of our approach is further demonstrated by twofold C−H arylations for the complexity‐increasing assembly of artificial peptides within a multicatalytic C−H activation manifold.

Bioorthogonal Diversification of Peptides through Selective Ruthenium(II)-Catalyzed C-H Activation.

Methods for the chemoselective modification of amino acids and peptides are powerful techniques in biomolecular chemistry. Among other applications, they enable the total synthesis of artificial peptides. In recent years, significant momentum has been gained by exploiting palladium-catalyzed cross-coupling for peptide modification. Despite major advances, the prefunctionalization elements on the coupling partners translate into undesired byproduct formation and lengthy synthetic operations. In sharp contrast, we herein illustrate the unprecedented use of versatile ruthenium(II)carboxylate catalysis for the step-economical late-stage diversification of α- and β-amino acids, as well as peptides, through chemo-selective C-H arylation under racemization-free reaction conditions. The ligand-accelerated C-H activation strategy proved water-tolerant and set the stage for direct fluorescence labelling as well as various modes of peptide ligation with excellent levels of positional selectivity in a bioorthogonal fashion. The synthetic utility of our approach is further demonstrated by twofold C-H arylations for the complexity-increasing assembly of artificial peptides within a multicatalytic C-H activation manifold.

ChemInform Abstract: Ruthenium‐Catalyzed C—H Alkynylation of Aromatic Amides with Hypervalent Iodine—Alkyne Reagents.

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.

Ruthenium-Catalyzed C-H Alkynylation of Aromatic Amides with Hypervalent Iodine-Alkyne Reagents.

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.

ChemInform Abstract: Ruthenium Carboxylate Complexes as Efficient Catalysts for the Addition of Carboxylic Acids to Propargylic Alcohols.

AbstractNewly synthesized ruthenium complexes are applied as catalysts in the addition of carboxylic acids to propargylic alcohols to give the corresponding β‐oxo esters in high yields even in air.

Cationic mononuclear ruthenium carboxylates as catalyst prototypes for self-induced hydrogenation of carboxylic acids.

Carboxylic acids are ubiquitous in bio-renewable and petrochemical sources of carbon. Hydrogenation of carboxylic acids to yield alcohols produces water as the only byproduct, and thus represents a possible next generation, sustainable method for the production of these alternative energy carriers/platform chemicals on a large scale. Reported herein are molecular insights into cationic mononuclear ruthenium carboxylates ([Ru(OCOR)]+) as prototypical catalysts for the hydrogenation of carboxylic acids. The substrate-derived coordinated carboxylate was found to function initially as a proton acceptor for the heterolytic cleavage of dihydrogen, and subsequently also as an acceptor for the hydride from [Ru–H]+, which was generated in the first step (self-induced catalysis). The hydrogenation proceeded selectively and at high levels of functional group tolerance, a feature that is challenging to achieve with existing heterogeneous/homogeneous catalyst systems. These fundamental insights are expected to significantly benefit the future development of metal carboxylate-catalysed hydrogenation processes of bio-renewable resources.

Ruthenium(II)-Catalyzed C–H Arylation of Azoarenes by Carboxylate Assistance

Ruthenium(II)carboxylate complexes enabled the unprecedented direct C–H arylation of azoarenes with aryl halides through chelation assistance. The mild reaction conditions of the optimized C–H functionalization process resulted in a remarkable functional group tolerance. The proximity-induced C–H arylation proceeded with high positional selectivity and could be performed in a one-pot protocol along with a azoarene reduction, providing expedient access to ortho-arylated anilines.

Ruthenium Carboxylate Complexes as Efficient Catalysts for the Addition of Carboxylic Acids to Propargylic Alcohols (Eur. J. Inorg. Chem. 18/2015)

Ruthenium Carboxylate Complexes as Efficient Catalysts for the Addition of Carboxylic Acids to Propargylic Alcohols (Eur. J. Inorg. Chem. 18/2015)

Ruthenium Carboxylate Complexes as Efficient Catalysts for the Addition of Carboxylic Acids to Propargylic Alcohols

AbstractInvited for the cover of this issue is the group of Heinrich Lang at the Technische Universität Chemnitz, Germany. The cover image shows the atom‐economical and highly selective addition of carboxylic acids to propargylic alcohols to give β‐oxopropyl esters. This conversion is catalyzed by ruthenium complexes, represented by the skater in our picture.

Ruthenium Carboxylate Complexes as Efficient Catalysts for the Addition of Carboxylic Acids to Propargylic Alcohols

AbstractRuthenium complexes [Ru(CO)2(PPh3)2(O2CR)2] – 3a (R = CH2OCH3), 3b (R = iPr), 3c (R = tBu), 3d (R = 2‐cC4H3O), and 3e (R = Ph) – were synthesized by treatment of Ru(CO)3(PPh3)2 with the corresponding carboxylic acids. The molecular structures of the newly synthesized complexes in the solid state are discussed. Compounds 3a–e were successfully applied as catalysts in the addition of carboxylic acids to propargylic alcohols to give the corresponding β‐oxo esters in good to excellent yields even in air. The different carboxylate ligands do not have an influence on the productivities, because the carboxylates exchange rapidly under the applied reaction conditions, as was confirmed by 31P{1H} NMR spectroscopic studies. The addition of catalytic amounts of Na2CO3 resulted in an increase in β‐oxo ester formation. The reaction is tolerant to the use of versatile functional groups on the propargylic alcohols and carboxylic acids, revealing a broad substrate generality. In contrast to most other known catalytic systems, even sterically hindered substrates, including 2,4,6‐trimethylbenzoic acid, 1,1‐diphenylprop‐2‐yn‐1‐ol, or the biologically active steroid ethisterone, were successfully converted.

Ruthenium(II)-catalyzed cross-dehydrogenative C–H alkenylations by triazole assistance

Ruthenium(II) carboxylate complexes allowed for efficient cross-dehydrogenative alkenylations of N-aryl-1,2,3-triazoles. The twofold C–H functionalizations occurred with excellent chemo-, regio-, site- and diastereoselectivities, and ample substrate scope. The versatile ruthenium(II) catalyst proved tolerant of moisture, air, and various electrophilic functional groups. Mechanistic studies were in good agreement with an initial C–H metalation by a cationic ruthenium(II) carboxylate, along with a subsequent migratory insertion of the olefin.