Active ruthenium‐(N‐heterocyclic carbene) complexes for hydrogenation of ketones

Four ruthenium‐N‐heterocyclic carbene complexes ( 3–6 ) have been prepared and the new compounds characterized by C, H, N analyses, ¹H‐NMR and ¹³C‐NMR. The reduction of ketones to alcohols via transfer hydrogenation was achieved with catalytic amounts of complexes 3–6 in the presence of t‐BuOK. Copyright © 2006 John Wiley & Sons, Ltd.     

Transfer hydrogenation of ketones catalysed by half‐sandwich (η6‐p‐cymene) ruthenium(II) complexes incorporating benzoylhydrazone ligands

Neutral half‐sandwich η⁶‐p ‐cymene ruthenium(II) complexes of general formula [Ru(η⁶‐p ‐cymene)Cl(L)] (HL = monobasic O, N bidendate benzoylhydrazone ligand) have been synthesized from the reaction of [Ru(η⁶‐p ‐cymene)(μ‐Cl)Cl]₂ with acetophenone benzoylhydrazone ligands. All the complexes have been characterized using analytical and spectroscopic (Fourier transform infrared, UV–visible, ¹H NMR, ¹³C NMR) techniques. The molecular structures of three of the complexes have been determined using single‐crystal X‐ray diffraction, indicating a pseudo‐octahedral geometry around the ruthenium(II) ion. All the ruthenium(II) arene complexes were explored as catalysts for transfer hydrogenation of a wide range of aromatic, cyclic and aliphatic ketones with 2‐propanol using 0.1 mol% catalyst loading, and conversions of up to 100% were obtained. Further, the influence of other variables on the transfer hydrogenation reaction, such as base, temperature, catalyst loading and substrate scope, was also investigated.     

Novel half‐sandwich η5‐Cp *–rhodium(III) and η5‐Cp *–ruthenium(II) complexes bearing bis(phosphino)amine ligands and their use in the transfer hydrogenation of aromatic ketones

Two new half‐sandwich η⁵‐Cp*–rhodium(III) and η⁵‐Cp*–ruthenium(II) complexes have been prepared from corresponding bis(phosphino)amine ligands, thiophene‐2‐(N,N‐bis(diphenylphosphino)methylamine) or furfuryl‐2‐(N,N‐bis(diphenylphosphino)amine). Structures of the new complexes have been elucidated by multinuclear one‐ and two‐dimensional NMR spectroscopy, elemental analysis and IR spectroscopy. These Cp*–rhodium(III) and Cp*‐ruthenium(II) complexes bearing bis(phosphino)amine ligands were successfully applied to transfer hydrogenation of various ketones by 2‐propanol. Copyright © 2013 John Wiley & Sons, Ltd.     

Donor‐Flexible Bis(pyridylidene amide) Ligands for Highly Efficient Ruthenium‐Catalyzed Olefin Oxidation

An exceptionally efficient ruthenium‐based catalyst for olefin oxidation has been designed by exploiting N,N′‐bis(pyridylidene)oxalamide (bisPYA) as a donor‐flexible ligand. The dynamic donor ability of the bisPYA ligand, imparted by variable zwitterionic and neutral resonance structure contributions, paired with the redox activity of ruthenium provided catalytic activity for Lemieux–Johnson‐type oxidative cleavage of olefins to efficiently prepare ketones and aldehydes. The ruthenium bisPYA complex significantly outperforms state‐of‐the‐art systems and displays extraordinary catalytic activity in this oxidation, reaching turnover frequencies of 650 000 h^?1 and turnover numbers of several millions.     

Hydrogenation of nitroaromatics to anilines catalyzed by air‐stable arene ruthenium (II)–NNN pincer complexes

A series of air‐stable, phosphine‐free arene ruthenium (II)–NNN pincer complexes (RuL, RuL¹, RuL² and RuL³) have been synthesized and characterized by spectroscopic and single‐crystal X‐ray analysis. Further, arene ruthenium (II)–NNN pincer complexes have been used as catalyst for hydrogenation of nitroaromatics into aniline in the presence of NaBH₄ at room temperature. The catalytic process suggested highly chemo‐selective nitroreduction with wide functional group tolerance.     

Ruthenium(II) complexes derived from 2‐phenylthiazoline‐4‐carboxylic acid: structure and catalytic activity for transfer hydrogenation reaction

Piano‐stool ([(p‐cymene)Ru(thz)Cl], 2 ) and six‐coordinated ([Ru(thz)₂(PPh₃)₂], 3 ) ruthenium complexes derived from 2‐phenylthiazoline‐4‐carboxylic acid (Hthz, 1 ) were synthesized for the first time, and fully characterized using conventional methods. Also, the molecular structure of complex 3 was determined using X‐ray analysis. These complexes were evaluated as catalysts for transfer hydrogenation of carbonyl compounds in the presence of isopropyl alcohol and KO^tBu. Complex 2 was found to be more active than 3 in transfer hydrogenation. Copyright © 2016 John Wiley & Sons, Ltd.     

Design of PEO‐based ruthenium carbene for aqueous metathesis polymerization. Synthesis by the “macromonomer method” and application in the miniemulsion metathesis polymerization of norbornene

Novel water‐soluble ruthenium carbene complexes with finely tuned structure and properties in solution are reported. These ruthenium‐based initiators were found to exhibit great catalytic activity in aqueous miniemulsion ring‐opening metathesis polymerization of norbornene. Stable particles of polynorbornene could be generated in the 200–250 nm size range stabilized with a nonionic surfactant (polystyrene‐b‐poly(ethylene oxide)). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2784–2793, 2006     

Half‐sandwich Ir (III) and Rh (III) complexes as catalysts for water oxidation with double‐site

A series of neutral binuclear iridium and rhodium complexes were synthesized based on bis‐imine ligands under mild conditions. These half‐sandwich late transition metal complexes were isolated in good yields and characterized by elemental analysis, ¹H NMR, ¹³C NMR, HR‐MS, and FT‐IR spectroscopies, and the solid state structure of complexes 1 and 2 were further confirmed by single‐crystal X‐ray diffraction. Cyclic voltammetry (CV) characterization indicated that the complex 1 has the best catalyst for water oxidation process with TOF of 0.8 s^?1 at low overpotential of 0.325 V in methanol‐phosphate buffer. The proposed double‐site water oxidation mechanism had been also speculated .     

Ruthenium(II) complexes of hybrid 8‐hydroxyquinoline–thiosemicarbazone ligands: synthesis,characterization and catalytic applications

A series of new hexa‐coordinated ruthenium(II) hydroxyquinoline–thiosemicarbazone complexes of the type [Ru(CO)(EPh₃)(B)(L)] (E = P or As; B = PPh₃, AsPh₃ or Py; L = hydroxyquinoline–thiosemicarbazone) were synthesized by reacting ruthenium precursor complexes [RuHCl(CO)(EPh₃)₂(B)] (E = P or As; B = PPh₃, AsPh₃ or Py) with hydroxyquinoline–thiosemicarbazone ligands in ethanol. The new complexes were characterized by analytical and spectroscopic (FT‐IR, UV–visible, NMR (¹H, ¹³C and ³¹P) and fast atom bombardment (FAB)–mass spectrometric methods. Based on the spectral results, an octahedral geometry was assigned for all the complexes. The new complexes showed good catalytic activity for the conversion of aldehydes to amides in the presence of hydroxylamine hydrochloride–sodium bicarbonate and for the oxidation of alkanes into their corresponding alcohols and ketones in the presence of m‐chloroperbenzoic acid. The complexes also catalyzed the N‐alkylation of benzylamine in the presence of KOtBu in alcohol medium. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis,structure and catalytic polymerization activity of half‐sandwich cyclometallated iridium complexes

A series of mononuclear half‐sandwich cyclometallated iridium complexes with Schiff base ligands were synthesized in good yields. Five air‐stable C,N‐chelate mode complexes were obtained smoothly through metal‐mediated C─H bond activation. Treatments of dimeric metal complexes [Cp*IrCl₂]₂ with ligands L1–L5 afforded the corresponding C,N‐chelate mononuclear half‐sandwich iridium(III) complexes 1 – 5 . These iridium complexes exhibit high catalytic activity for norbornene polymerization. Both steric and electronic effects of the substituted groups have influences on the behaviors of the polymerization process. All complexes were characterized using infrared and NMR spectroscopies and elemental analysis. Molecular structures of complexes 1 , 2 and 5 were further confirmed using single‐crystal X‐ray analysis.     

Transfer hydrogenation of aryl ketones with homogeneous ruthenium catalysts containing diazafluorene ligands

Novel cationic ruthenium(II) complexes bearing a 4,5‐diazafluorene unit and p‐cymene as ligands have been synthesised. The complexes were characterised based on elemental analysis and Fourier transform infrared and nuclear magnetic resonance spectroscopies. The synthesised Ru(II) complexes were employed as pre‐catalysts for the transfer hydrogenation of aromatic ketones using 2‐propanol as both hydrogen source and solvent in the presence of NaOH. All complexes showed high catalytic activity as catalysts in the reduction of substituted acetophenones to corresponding secondary alcohols. The products of catalysis were obtained with conversion rates of between 80 and 99%. Among the seven new complexes investigated, the most efficient catalyst showed turnover frequencies in the range 255–291 h^?1 corresponding to 85 to 97% conversion, respectively. Copyright © 2016 John Wiley & Sons, Ltd.     

钌-膦-二胺配合物的电子效应对选择氢化C=C和C=O键的影响

本文合成了一系列新的钌-膦-二胺配合物,并通过核磁和元素分析表征确定了配合物的组分和结构。文中进一步考察了这些配合物用于苄叉丙酮以及苯乙酮和苯乙烯组成的混合物的选择催化加氢,发现随着膦和二胺配体中配位原子碱性的增强,羰基加氢的活性和选择性大幅提高;反之,配位原子碱性减弱不仅降低反应活性,羰基加氢的选择性也大幅降低。基于这些配合物的电子效应对催化氢化性质的影响,我们提出了在钌-膦-二胺体系中的氢活化机理。     

Studies on synthesis of quinonylidene Hoveyda‐type complexes

In a quest of redox‐switchable metathesis catalysts we attempted synthesis of ruthenium quinonylidene complexes using two synthetic pathways. First, Hoveyda‐type complexes bearing chelating benzylidene and naphthylidene ligands substituted with two alkoxy/hydroxy groups were synthesized and characterized. The catalysts were tested in model ring‐closing metathesis reactions, and displayed interesting correlations between structure and catalytic activity. Unfortunately, numerous attempts at oxidation of the complexes to derivatives of benzo‐ and naphthoquinone were unsuccessful. However, the second approach, using exchange reaction of ruthenium precursor with vinylquinone ligand, gave a transient unstable product observed with ¹H NMR. The experimental data suggest that conjugation of electron‐deficient quinones to the ruthenium centre results in intrinsically unstable species, which undergo secondary reactions under ambient conditions. Copyright © 2015 John Wiley & Sons, Ltd.     

Ruthenium carbonyl complexes in catalytic epoxidation of olefins co‐catalyzed by isobutyl‐aldehyde

The present work shows the catalytic activity of a series of carbonyl ruthenium complexes in the epoxidation of olefins co‐catalyzed by isobutyl‐aldehyde. The complexes display catalytic activity in the epoxidation of the cyclohexene with high selectivity. Copyright © 2006 John Wiley & Sons, Ltd.     

Ru–η6‐benzene–phosphine complex‐catalyzed transfer hydrogenation of ketones

Three Ru–η⁶‐benzene–phosphine complexes bearing tri‐(p‐methoxyphenyl)phosphine, triphenylphosphine and tri‐(p‐trifluoromethylphenyl)phosphine were synthesized and characterized by ³¹P{¹H} NMR, ¹H NMR, ¹³C{¹H} NMR and elemental analyses. Complex 1 was further identified by X‐ray crystallography. These complexes exhibit good to excellent activities for the transfer hydrogenation of ketones in refluxing 2‐propanol, and the highest turnover frequency (TOF) is up to 5940 h⁻¹. The effect of electronic factors of these complexes on the transfer hydrogenation of ketones reveals that the catalytic activity is promoted by electron‐donating phosphine and the catalyst stability is improved by electron‐withdrawing phosphine. Copyright © 2011 John Wiley & Sons, Ltd.     

Redox Control of a Dendritic Ferrocenyl‐Based Homogeneous Catalyst

The application of a dendrimer in a redox‐switchable catalytic process is reported. A monomeric and the corresponding dendritic ferrocenylphosphane ligand were used to develop well‐defined controllable catalysts with distinct redox states. The corresponding ruthenium(II) complexes catalyze the isomerization of the allylic alcohol 1‐octen‐3‐ol. By adding a chemical oxidant or reductant, it was possible to reversibly switch the catalytic activity of the complexes. On oxidation, the ferrocenium moiety withdraws electron density from the phosphane, thereby lowering its basicity. The resulting electron‐poor ruthenium center shows much lower activity for the redox isomerization and the reaction rate is markedly reduced.     

Anticancer Activity of Hydrogen‐Bond‐Stabilized Half‐Sandwich RuII Complexes with Heterocycles

Neutral half‐sandwich organometallic ruthenium(II) complexes of the type [(η⁶‐cymene)RuCl₂(L)] ( H1 – H10 ), where L represents a heterocyclic ligand, have been synthesized and characterized spectroscopically. The structures of five complexes were also established by single‐crystal X‐ray diffraction confirming a piano‐stool geometry with η⁶ coordination of the arene ligand. Hydrogen bonding between the N? H group of the heterocycle and a chlorine atom attached to Ru stabilizes the metal–ligand interaction. Complexes coordinated to a mercaptobenzothiazole framework ( H1 ) or mercaptobenzoxazole ( H6 ) showed high cytotoxicity against several cancer cells but not against normal cells. In vitro studies have shown that the inhibition of cancer cell growth involves primarily G1‐phase arrest as well as the generation of reactive oxygen species (ROS). The complexes are found to bind DNA in a non‐intercalative fashion and cause unwinding of plasmid DNA in a cell‐free medium. Surprisingly, the cytotoxic complexes H1 and H6 differ in their interaction with DNA, as observed by biophysical studies, they either cause a biphasic melting of the DNA or the inhibition of topoisomerase IIα activity, respectively. Substitution of the aromatic ring of the heterocycle or adding a second hydrogen‐bond donor on the heterocycle reduces the cytotoxicity.     

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,characterization and catalytic,cytotoxic and antimicrobial activities of two novel cyclotriphosphazene‐based multisite ligands and their Ru(II) complexes

Two novel cyclotriphosphazene ligands ( 2 and 3 ) bearing 3‐oxypyridine groups and their corresponding Ru(II) complexes ( 4 and 5 ) were synthesized and their structures were characterized using Fourier transform infrared, ¹H NMR and ³¹P NMR spectroscopic data and elemental analysis. The Ru(II) complexes were used as catalysts for catalytic transfer hydrogenation of p‐substituted acetophenone derivatives in the presence of KOH. Additionally, the cytotoxic activities of compounds 2 , 3 , 4 , 5 were evaluated against PC3 (human prostate cancer), DLD‐1 (human colorectal cancer), HeLa (human cervical cancer) and PNT1A (normal human prostate) cell lines. Finally the antimicrobial activities of compounds 2 , 3 , 4 , 5 were evaluated against a panel of Gram‐positive and Gram‐negative bacteria and yeast cultures. The complexes showed efficient catalytic activity towards transfer hydrogenation of acetophenone derivatives, especially those bearing electron‐withdrawing substituents on the para‐position of the aryl ring. The compounds were found to have moderate to high cytotoxic and antimicrobial activities, and Ru(II) complexation enhanced both cytotoxic and antimicrobial activities in comparison with the parent compounds. Copyright © 2015 John Wiley & Sons, Ltd.     

Catalytic Water Oxidation by Ruthenium(II) Quaterpyridine (qpy) Complexes: Evidence for Ruthenium(III) qpy‐N,N′′′‐dioxide as the Real Catalysts

Polypyridyl and related ligands have been widely used for the development of water oxidation catalysts. Supposedly these ligands are oxidation‐resistant and can stabilize high‐oxidation‐state intermediates. In this work a series of ruthenium(II) complexes [Ru(qpy)(L)₂]²⁺ (qpy=2,2′:6′,2′′:6′′,2′′′‐quaterpyridine; L=substituted pyridine) have been synthesized and found to catalyze Ce^IV‐driven water oxidation, with turnover numbers of up to 2100. However, these ruthenium complexes are found to function only as precatalysts; first, they have to be oxidized to the qpy‐N,N′′′‐dioxide (ONNO) complexes [Ru(ONNO)(L)₂]³⁺ which are the real catalysts for water oxidation.