Half-sandwich arene ruthenium complexes: synthetic strategies and relevance in catalysis

Stacking interactions of the methylated cyclopentadienyl ligands in the crystal structures of transition metal complexes

In the crystal structures of methylated cyclopentadienyl (Cp) complexes (MeCp, Me₄Cp and Me₅Cp) deposited in the Cambridge Structural Database, certain orientation types of stacked contacts can be noted as the most frequent. These orientation preferences can be well explained by the matching of oppositely charged regions of electrostatic potential. Parallel displaced stacking, large offset stacking and C-H...π interactions are the dominant interaction types that are responsible for the arrangement in the crystal structures of stacked methylated Cp complexes.

Half-sandwich ruthenium(ii) complexes with tethered arene-phosphinite ligands: synthesis, structure and application in catalytic cross dehydrogenative coupling reactions of silanes and alcohols

The preparation of the tethered arene-ruthenium(ii) complexes [RuCl₂{η⁶:κ¹(P)-C₆H₅(CH₂)_nOPR₂}] (R = Ph, n = 1 (9a), 2 (9b), 3 (9c); R = ⁱPr, n = 1 (10a), 2 (10b), 3 (10c)) from the corresponding phosphinite ligands R₂PO(CH₂)_nPh (R = Ph, n = 1 (1a), 2 (1b), 3 (1c); R = ⁱPr, n = 1 (2a), 2 (2b), 3 (2c)) is presented. Thus, in a first step, the treatment at room temperature of tetrahydrofuran solutions of dimers [{RuCl(μ-Cl)(η⁶-arene)}₂] (arene = p-cymene (3), benzene (4)) with 1-2a-c led to the clean formation of the corresponding mononuclear derivatives [RuCl₂(η⁶-p-cymene){R₂PO(CH₂)_nPh}] (5-6a-c) and [RuCl₂(η⁶-benzene){R₂PO(CH₂)_nPh}] (7-8a-c), which were isolated in 66-99% yield. The subsequent heating of 1,2-dichloroethane solutions of these compounds at 120 °C allowed the exchange of the coordinated arene. The substitution process proceeded faster with the benzene derivatives 7-8a-c, from which complexes 9-10a-c were generated in 61-82% yield after 0.5-10 h of heating. The molecular structures of [RuCl₂(η⁶-p-cymene){ⁱPr₂PO(CH₂)₃Ph}] (6c) and [RuCl₂{η⁶:κ¹(P)-C₆H₅(CH₂)_nOPⁱPr₂}] (n = 1 (10a), 2 (10b), 3 (10c)) were unequivocally confirmed by X-ray diffraction methods. In addition, complexes [RuCl₂{η⁶:κ¹(P)-C₆H₅(CH₂)_nOPR₂}] (9-10a-c) proved to be active catalysts for the dehydrogenative coupling of hydrosilanes and alcohols under mild conditions (r.t.). The best results were obtained with [RuCl₂{η⁶:κ¹(P)-C₆H₅(CH₂)₃OPⁱPr₂}] (10c), which reached TOF and TON values up to 117 600 h^-1 and 57 000, respectively.

Methyl Ester Functionalized Phenalenyl Arene- and Bipyridine-Ruthenium-Based Complexes for Electroactive Langmuir-Blodgett Films

We report the synthesis of a new phenalenyl ligand, functionalized with a methyl ester electron withdrawing group, named 9-hydroxy-1-oxo-1 H-phenalen-5-methyl carboxylate (L), and the generated complexes [Ru(bpy)₂L]PF₆ and [(η⁶-C₆H₆)Ru(L)Cl]. Compounds were characterized by spectroscopic and X-ray diffraction methods, and their electrochemical behavior was investigated via cyclic voltammetry and UV-vis spectroelectrochemistry. The one-electron oxidized compounds have an unpaired electron located in the phenalenyl ring, as supported by theoretical calculations (DFT) and EPR results. Langmuir-Blodgett (LB) films deposited by [Ru(bpy)₂L]^2+/3+ species mixed with stearic acid are electroactive, showing a quasi-reversible wave with E_1/2^Film1 = 0.74 V and E_1/2^Film2 = 0.81, which are promising systems that allow access to immobilized open-shell species in the film.

Tandem transfer hydrogenation–epoxidation of ketone substrates catalysed by alkene-tethered Ru(ii)–NHC complexes

Eight novel alkene-tethered Ru(ii)–NHC complexes were employed as catalysts in tandem transfer hydrogenation–epoxidation reactions using phenacyl bromide derivatives as substrates.

Oxidative radical addition–chlorination of alkenes to access 1,1-dichloroalkanes from simple reagents

This protocol provides a facile regioselective method for the synthesis of 1,1-dichloroalkanes from terminal alkenes using simple chloro reagents.

Catalytic hydrogenation of carbonyl and nitro compounds using an [N,O]-chelate half-sandwich ruthenium catalyst

A series of N,O-chelate half-sandwich ruthenium complexes have been synthesized, which exhibited high activity for the catalytic hydrogenation of carbonyl and nitro compounds in aqueous solution.

Anticancer and antimicrobial properties of novel η6-p-cymene ruthenium(ii) complexes containing a N,S-type ligand, their structural and theoretical characterization

Ruthenium(ii) complexes are lately of great scientific interest due to their chemotherapeutic potential as anticancer and antimicrobial agents. Here we present the synthesis of new pyrazole carbothioamide derivatives and their four arene–ruthenium complexes. The title compounds were characterized with the application of IR, NMR, mass spectrometry, elemental analysis and X-ray diffraction. Additionally, for new complexes DFT calculations were done. Their antimicrobial activity (MIC, MBC/MFC) was examined in vitro against Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecalis, Pseudomonas aeruginosa, Proteus vulgaris and Candida albicans. Their cytotoxic effects, using the MTT assay, against three cancer cell lines: HL-60, NALM-6, WM-115 and normal human foreskin fibroblasts (HFF-1) were also investigated. The influence of the new arene–ruthenium(ii) complexes on the DNA structure was also tested. From our results, compound 2d showed higher cytotoxicity against melanoma cell line WM-115 than cisplatin. Strong biostatic and biocidal activity of the tested complexes against Gram-positive bacteria, including S. aureus, S. epidermidis and E. faecalis was demonstrated. The new arene–ruthenium(ii) compounds could not only inhibit proliferation of cancer cells, but also protect patients against malignant wound infections.

New arene–ruthenium(ii) complexes with pyrazole derivatives as ligands were synthesized and characterized. This compounds exhibited good cytotoxic effects, and strong biostatic and biocidal activity.

Reactions in Water - A Greener Approach Using Ruthenium Catalysts

Reactions using transition metals as catalysts have emerged as an efficient method in the recent times. However, the selection of solvent plays a crucial role in this regard. Several solvents used traditionally suffer majorly with problems of toxicity; high boiling point etc. leading to drastic reaction conditions. Water being a non-toxic, non-inflammable and environmentally benign can replace the hazardous organic solvents in laboratory as well as industry. Maintaining a minimum catalyst loading percentage we can advantageously avail high levels of selectivity. Water was found to be a good solvent medium for several metal catalysed reactions. An intramolecular deprotonation mechanism is followed by the ruthenium (II) catalysts in water; thereby, facilitating the catalytic action of the metal. These studies can help the industrial chemists to utilize water as a solvent for their reactions towards improvement of their waste management procedure. This review mainly focuses on the several recent developments in the above direction.

Crystallographic evidence for unexpected selective tyrosine hydroxylations in an aerated achiral Ru-papain conjugate

The X-ray structure of an aerated achiral Ru-papain conjugate has revealed the hydroxylation of two tyrosine residues found near the ruthenium ion. The most likely mechanism involves a ruthenium-bound superoxide as the reactive species responsible for the first hydroxylation and the resulting high valent Ru(iv)[double bond, length as m-dash]O species for the second one.

Crystal structure of (η 6-1-isopropyl-4-methyl benzene)-(N-(2,5-dichlorophenyl)-1-(pyridin-2-yl)methanimine-κ2 N,N′)ruthenium(II) perchlorate, C22H22Cl4N2O4Ru

C22H22Cl4N2O4Ru, monoclinic, P21/c (no. 14), a = 15.0181(3) Å, b = 10.3983(2) Å, c = 16.6496(3) Å, β = 112.459(1)°, V = 2402.84(8) Å3, Z = 4, R gt(F) = 0.0180, wR ref(F 2) = 0.0474, T = 173(2) K.

Cyclopentadienyl-Ru(II)-Pyridylamine Complexes: Synthesis, X-ray Structure, and Application in Catalytic Transformation of Bio-Derived Furans to Levulinic Acid and Diketones in Water

A series of cationic half-sandwich cyclopentadienyl-ruthenium(II)-pyridylamine complexes, [(η⁵-C₅H₅)Ru(κ²-L)(PPh₃)]⁺ (L = N_amine-substituted pyridylamine ligands) ([Ru]-1-[Ru]-6), along with the analogous cyclopentadienyl-ruthenium(II)- N-isopropylpyridylimine complex [(η⁵-C₅H₅)Ru(κ²-L)(PPh₃)]⁺ (L = N-isopropylpyridylimine) ([Ru]-7), have been synthesized in good yields. Structural identities of all the complexes have been authenticated by ¹H, ¹³C, and ³¹P NMR, mass spectrometry, and X-ray crystallography. The synthesized complexes exhibited high catalytic activity for the transformation of the bio-derived furans, 2-furfural (furfural), 5-methyl-2-furfural (5-MF), and 5-hydroxymethyl-2-furfural (5-HMF) to levulinic acid (LA) and the diketones, 3-hydroxyhexane-2,5-dione (3-HHD), 1-hydroxyhexane-2,5-dione (1-HHD), and hexane-2,5-dione (HD) in water. Efficient transformation of furfural to LA over a range of η⁵-Cp-Ru-pyridylamine complexes is substantially affected by the N_amine-substituents, where a η⁵-Cp-Ru- N-propylpyridylamine complex ([Ru]-2) exhibited higher catalytic activity in comparison to other η⁵-Cp-Ru-pyridylamine and η⁵-Cp-Ru-pyridylimine complexes. The relative catalytic activity of the studied complexes demonstrated a substantial structure-activity relationship which is governed by the basicity of N_amine, steric hindrance at N_amine, and the hemilabile nature of the coordinated pyridylamine ligands.

Water-soluble superbulky (η6-p-cymene) ruthenium(ii) amine: an active catalyst in the oxidative homocoupling of arylboronic acids and the hydration of organonitriles

Water-soluble superbulky (η⁶-p-cymene) ruthenium(ii) amine complex mediated oxidative homocoupling of arylboronic acids and the hydration of organonitriles are reported.

TD DFT insights into unusual properties of excited sandwich complexes: structural transformations and vibronic interactions in Rydberg-state bis(η6-benzene)chromium

TD DFT calculations reveal specific features of the Jahn–Teller effect in the lowest Rydberg p state of a prototypical sandwich molecule.

Stereoretentive Ligand Exchange Reactions of N-Fused Porphyrin Ruthenium(II) Complexes

The ligand exchange reactions of the ruthenium(II) complex of N-fused tetraphenylporphyrin, Ru(NFp)(CO)₂Cl (2), with various anions were investigated. The chloride ligand of the isomers 2a-c was stereoretentively exchanged with bromide (Br^-), iodide (I^-), and acetate (AcO^-) anions in toluene at 100 °C, structures of which were confirmed by ¹H NMR as well as single crystal X-ray diffraction analysis. The silver (AgOAc, AgOTf) and boron (NaBPh₄) reagents also afforded the corresponding stereoretentive products. On the other hand, the reaction with NaBH₄ afforded the hydride complex Ru(NFp)(CO)₂H (7) with low stereospecificity, showing a higher reactivity of 2c than other isomers. The ligand dissociation mechanism was proposed with the help of theoretical calculations on the plausible five-coordinated intermediates.

Chiral Sulfur Functional Groups as Definers of the Chirality at the Metal in Ir and Rh Half-Sandwich Complexes: A Combined CD/X-ray Study

Mesoionic carbenes (MICs) derived from triazolium salts that contain chiral sulfoxide or sulfoximine functional groups were used to construct enantiopure chiral-at-metal Ir^III and Rh^III half-sandwich complexes through the synthetic sequence of MIC complexation/C-H aromatic activation. The process was efficient and diastereoselective for the formation of enantiopure five-membered metallacycles. The use of the enantiomers of the chiral sulfur groups allowed us to prepare complexes that had opposite configurations at the metal center. Complete retention of the configuration at the metal center was observed during the formation of cationic Ir^III complexes and upon insertion of alkynes into the Ir^III -C bond, as demonstrated by a combined circular dichroism/X-ray study. These results point to a vicinal-assisted S_N 1-like mechanism.

Review for chiral-at-metal complexes and metal-organic framework enantiomorphs

This review discusses chiral-at-metal complexes and introduces enantiomorphs from assembly structure. Owing to the diverse coordination number and activity of metal ions as chiral centers, abundant structures for chiral selectivity, catalysis, and polarized light-response are the notable advantages of the chiral-at-metal complexes. The rational design and preparation of linear multi-dentate ligands is a good choice to improve the stability of chiral complexes, such as multi-bonding structure for high stability as a self-limiting system. The bio-significance and potential application of chiral-at-metal complexes are discussed, such as the synergistic effect of catalysis and chiral selectivity of the metal center in enzymes. Enzyme could be remolded to replace the original central metal ions with highly active rare earth or precious metal ions to form artificial metalloenzyme or to remove the "redundant" part around the metal center to improve the accessibility of substrate. The polarized light-response mechanism of chiral opsin is introduced in relation to its role in animal migration. Metal-organic frameworks (MOFs) are crystalline and porous materials built from metal nodes or clusters and organic linkers and provide the possibility to prepare artificial enantiomorphs. The preparations, applications, and characterization methods of MOF enatiomorphs are therefore introduced. We hope this review inspires researchers at all levels of their career to consider the title topic in their own research in terms of its application and potential value.

Crystal structure of (η 6-benzene)-(N-(2,6-dimethylphenyl)-1-(pyridin-2-yl)methanimine-κ2 N,N′)ruthenium(II) perchlorate monohydrate, C20H20Cl2N2O5Ru

C20H20Cl2N2O5Ru, monoclinic, P1̅ (no. 2), a = 8.7921(2) Å, b = 11.2515(3) Å, c = 11.7014(3) Å, α = 103.752(1)°, β = 107.296(1)°, γ = 98.562(1)°, V = 1043.01(5) Å3, Z = 2, R gt(F) = 0.0198, wR ref(F 2) = 0.0553, T = 173 K.

Crystal structure of chlorido-(N-(2,5-dichlorophenyl)-1-(pyridin-2-yl)methanimine-κ2 N,N′)(η 6-1-isopropyl-4-methyl benzene) ruthenium (II) tetrafluoroborate, C22H22Cl3N2BF4Ru

C22H22Cl3N2BF4Ru, monoclinic, P21/n (no. 14), a = 15.067(5) Å, b = 10.409(5) Å, c = 16.503(5) Å, β = 112.75(5)°, V = 2386.9(16) Å3, Z = 4, R gt(F) = 0.0211, wR ref(F 2) = 0.0535, T = 173 K.

Iminophosphanes: Synthesis, Rhodium Complexes, and Ruthenium(II)-Catalyzed Hydration of Nitriles

Highly stable iminophosphanes, obtained from alkylating nitriles and reaction of the resulting nitrilium ions with secondary phosphanes, were explored as tunable P-monodentate and 1,3-P,N bidentate ligands in rhodium complexes. X-ray crystal structures are reported for both κ¹ and κ² complexes with the counterion in one of them being an unusual anionic coordination polymer of silver triflate. The iminophosphane-based ruthenium(II)-catalyzed hydration of benzonitrile in 1,2-dimethoxyethane (180 °C, 3 h) and water (100 °C, 24 h) and under solvent free conditions (180 °C, 3 h) results in all cases in the selective formation of benzamide with yields of up to 96%, thereby outperforming by far the reactions in which the common 2-pyridyldiphenylphosphane is used as the 1,3-P,N ligand.

Crystal structure of chlorido-(η6–1-isopropyl-4-methyl benzene)-(1-(pyridin-2-yl)-N-(p-tolyl)methanimine-κ2 N,N′)ruthenium(II) hexafluorophosphate(V), C23H26ClF6N2PRu

C23H26ClF6N2PRu, triclinic, P1̅ (no. 2), a = 8.9950(6) Å, b = 11.1669(8) Å, c = 12.4128(9) Å, α = 80.520(2)°, β = 87.5360(10)°, γ = 86.3200(10)°, V = 1226.59(15) Å3, Z = 2, R gt(F) = 0.0267, wR ref(F 2) = 0.0622, T = 173(2) K.