Protic- or anionic-NHCs with a classical-NHC in a single [Ru(CNC)(PPh3)2Cl]Cl pincer complex: direct comparison of structure & electronic properties and heterolytic H2 splitting.

Herein, we report the first set of pincer complexes 1 and 2 with the general formula [Ru(CNC)(PPh3)2Cl]Cl having a protic- and classical-NHC in the same molecule and nearly identical environments. Deprotonation of the protic-NHC complex 2 with one equivalent of base leads to the formation of anionic-NHC complex 2'. These complexes allow a direct comparison of protic- and anionic-NHCs with the classical-NHC ligand. A comparison of the molecular structure indicated that the metal carbene bond length trend is anionic-NHC > protic-NHC > classical-NHC. The electrochemical investigation revealed the electron donation tendency is classical-NHC > protic-NHC and anionic-NHC > protic-NHC. Cooperation between the metal and the ligand is indicated by the reaction of 2' with H2 gas at 1 atm pressure and 110 °C to give the Ru-hydride complex 3.

Role of ancillary ligands in selectivity towards acceptorless dehydrogenation versus dehydrogenative coupling of alcohols and amines catalyzed by cationic ruthenium(II)-CNC pincer complexes.

An unexpected reversal in catalytic activity for acceptorless dehydrogenative coupling compared to acceptorless alcohol dehydrogenation has been observed using a series of cationic Ru(II)-CNC pincer complexes with different ancillary ligands. In continuation of our study of cationic Ru(II)-CNC pincer complexes 1a-6a, new complexes with bulky N-wingtips [Ru(CNCiPr)(CO)(PPh3)Br]PF6 (1b), [Ru(CNCCy)(CO)(PPh3)Cl]PF6 (1c), [Ru(CNCCy)(CO)(PPh3)H]PF6 (2c), [Ru(CNCiPr)(PPh3)2Cl]PF6 (3b), [Ru(CNCCy)(PPh3)2Cl]PF6 (3c), [Ru(CNCiPr)(PPh3)2H]PF6 (4b), [Ru(CNCCy)(PPh3)2H]PF6 (4c), [Ru(CNCiPr)(DMSO)2Cl]PF6 (6b), and [Ru(CNCCy)(DMSO)2Cl]PF6 (6c) [CNCR = 2,6-bis(1-alkylimidazol-2-ylidene)-pyridine] have been synthesized and the catalytic activities of the new complexes have been compared with their N-methyl analogues for transfer hydrogenation of cyclohexanone and acceptorless dehydrogenation of benzyl alcohol. Furthermore, all complexes have been utilized as catalysts in the dehydrogenative coupling reaction of benzyl alcohol with amines. While the catalytic activities of the new complexes for transfer hydrogenation and acceptorless alcohol dehydrogenation were found to be in line with the previously observed trend based on the ancillary ligands (CO > COD > DMSO > PPh3), for the acceptorless dehydrogenative coupling reaction, complexes containing PPh3 and DMSO ligands performed better compared to complexes containing CO and COD ligands. Based on NMR and mass investigation of catalytic reactions, a plausible mechanism has been suggested to explain the difference in catalytic activity and its reversal during the dehydrogenative coupling reaction. Furthermore, the substrate scope for the dehydrogenative coupling reaction of benzyl alcohol with a wide range of amines has been explored, including synthesizing some pharmaceutically important imines. All new complexes have been characterized by various spectroscopic techniques, and the structures of 4b and 6b have been confirmed by the single-crystal X-ray diffraction technique.

Ru(II) Complexes with Protic- and Anionic-Naked-NHC Ligands for Cooperative Activation of Small Molecules.

A set of ruthenium(II)-protic-N-heterocyclic carbene complexes, [Ru(NNCH )(PPh3 )2 (X)]Cl (1, X=Cl and 2, X=H) and their deprotonated forms [Ru(NNC)(PPh3 )2 (X)] (1', X=Cl and 2', X=H), in which NNC is a new unsymmetrical pincer ligand, are reported. The four complexes are interconvertible by simple acid-base chemistry. The combined theoretical and spectroscopic investigations indicate charge segregation in anionic-NHC complexes (1' and 2') and can be described from a Lewis pair perspective. The chemical reactivity of deprotonated complex 1' shows cooperative small molecule activation. Complex 1' activates H-H bond of hydrogen, C(sp3 )-I bond of iodomethane, and C(sp)-H bond of phenylacetylene. The activation of CO2 using anionic NHC complex 1' at moderate temperature and ambient pressure and subsequent conversion to formate is also described. All the new compounds have been characterized using ESI-MS, 1 H, 13 C, and 31 P NMR spectroscopy. Molecular structures of 1, 2, and 2' have also been determined with single-crystal X-ray diffraction. The cooperative small molecule activation perspective broadens the scope of potential applications of anionic-NHC complexes in small molecule activation, including the conversion of carbon dioxide to formate, a much sought after reaction in the renewable energy and sustainable development domains.

Base-free synthesis of benchtop stable Ru(III)-NHC complexes from RuCl3·3H2O and their use as precursors for Ru(II)-NHC complexes.

A series of Ru(III)-NHC complexes, identified as [RuIII(PyNHCR)(Cl)3(H2O)] (1a-c), have been prepared, starting from RuCl3·3H2O following a base-free route. The Lewis acidic Ru(III) centre operates via a halide-assisted, electrophilic C-H activation for carbene generation. The best results were obtained with azolium salts having the I- anion, while ligand precursors with Cl-, BF4-, and PF6- gave no complex formation and those with Br- gave a product with mixed halides. The structurally simple, air and moisture-stable complexes represent rare examples of paramagnetic Ru(III)-NHC complexes. Furthermore, these benchtop stable Ru(III)-NHC complexes were shown to be excellent metal precursors for the synthesis of new [RuII(PyNHCR)(Cl)2(PPh3)2] (2a-c) and [RuII(PyNHCR)(CNCMe)I]PF6 (3a-c) complexes. All the complexes have been characterised using spectroscopic methods, and the structures of 1a, 1b, 2c, and 3a have been determined using the single-crystal X-ray diffraction technique. This work allows easy access to new Ru-NHC complexes for the study of new properties and novel applications.

Transformation of Battery to High Performance Pseudocapacitor by the Hybridization of W18O49 with RuO2 Nanostructures.

Defects such as oxygen vacancy in the nanostructures have paramount importance in tuning the optical and electronic properties of a metal oxide. Here we report the growth of oxygen deficit tungsten oxide (W18O49) nanorods modified with ruthenium oxide (RuO2) using a simple and economical hydrothermal approach for energy storage application. In this work, a novel approach of hybridizing the W18O49 nanostructure with RuO2 to control the electrochemical performance for energy storage applications has been proposed. The result displays that the hybridization of the nanostructures plays an important role in yielding high specific capacitance of the electrode material. Due to the augmentation of W18O49 and RuO2 nanostructures, the galvanostatic charging and discharging (GCD) mechanism exhibited the transformation from the battery type characteristics of W18O49 into the typical pseudocapacitor feature of hybrid architect nanostructure due to defect creations. The electrochemical measurement of hybrid nanomaterial shows the doubling of specific capacitance to 1126 F/g and 1050 F/g in cyclic voltammetry (CV) and GCD, respectively, in comparison with W18O49 and RuO2 and earlier reports. The enhancement in the stability performance up to 3000 cycles of hybrid is indebted to the stable nature of W18O49 and the high conductivity of RuO2.

Asymmetric hydrogenation of an α-unsaturated carboxylic acid catalyzed by intact chiral transition metal carbonyl clusters - diastereomeric control of enantioselectivity.

Twenty clusters of the general formula [(µ-H)2Ru3(µ3-S)(CO)7(µ-P-P*)] (P-P* = chiral diphosphine of the ferrocene-based Walphos or Josiphos families) have been synthesised and characterised. The clusters have been tested as catalysts for asymmetric hydrogenation of tiglic acid [trans-2-methyl-2-butenoic acid]. The observed enantioselectivities and conversion rates strongly support catalysis by intact Ru3 clusters. A catalytic mechanism involving an active Ru3 catalyst generated by CO loss from [(µ-H)2Ru3(µ3-S)(CO)7(µ-P-P*)] has been investigated by DFT calculations.

Selective and Recyclable Congo Red Dye Adsorption by Spherical Fe3O4 Nanoparticles Functionalized with 1,2,4,5-Benzenetetracarboxylic Acid.

In this study, the new material Fe3O4@BTCA has been synthesized by immobilization of 1,2,4,5-Benzenetetracarboxylic acid (BTCA) on the surface of Fe3O4 NPs, obtained by co-precipitation of FeCl3.6H2O and FeCl2.4H2O in the basic conditions. Characterization by P-XRD, FE-SEM, and TEM confirm Fe3O4 has a spherical crystalline structure with an average diameter of 15 nm, which after functionalization with BTCA, increases to 20 nm. Functionalization also enhances the surface area and surface charge of the material, confirmed by BET and zeta potential analyses, respectively. The dye adsorption capacity of Fe3O4@BTCA has been investigated for three common dyes; Congo red (C.R), Methylene blue (M.B), and Crystal violet (C.V). The adsorption studies show that the material rapidly and selectively adsorbs C.R dye with very high adsorption capacity (630 mg/g), which is attributed to strong H-bonding ability of BTCA with C.R dye as indicated by adsorption mechanism study. The material also shows excellent recyclability without any considerable loss of adsorption capacity. Adsorption isotherm and kinetic studies suggest that the adsorption occurs by the Langmuir adsorption model following pseudo-second-order adsorption kinetics.

Electronic and Structural Comparisons between Iron(II/III) and Ruthenium(II/III) Imide Analogs.

To examine structural and electronic differences between iron and ruthenium imido complexes, a series of compounds was prepared with different phosphine basal sets. The starting material for the ruthenium complexes was Ru(NAr/Ar*)(PMe3)3 (Ru1/Ru1*), where Ar = 2,6-(iPr)2C6H3 and Ar* = 2,4,6-(iPr)3C6H2, which were prepared from cis-RuCl2(PMe3)4 and 2 equiv of LiNHAr/Ar*. The starting materials for the iron complexes were the analogous Fe(NAr/Ar*)(PMe3)3 species (Fe1/Fe1*), which were not isolated but could be generated in situ from FeCl2, PMe3, and LiNHAr/Ar*. With both iron and ruthenium, the PMe3 starting materials underwent phosphine replacement with chelating ligands to give new group 8 imido complexes in the +2 oxidation state. Addition of 1,2-bis(diphenylphosphino)ethane (dppe) to M1/M1* gave Ru(NAr/Ar*)(PMe3)(dppe) and Fe(NAr/Ar*)(PMe3)(dppe). Addition of 1,2-bis(dimethylphosphino)ethane (dmpe) provided Ru(NAr/Ar*)(dmpe)2. A triphos ligand, {P(Me)2CH2}3SitBu (tP3), was also examined. Addition of tP3 to Fe1 provided Fe(NAr)(tP3) (Fe4), but a similar reaction with Ru1 only gave intractable materials. Oxidation of Fe4 with AgSbF6 gave {Fe(NAr)(tP3)}+SbF6- (Fe4a). Oxidation of Ru2 with AgSbF6 gave the unstable cation {Ru(NAr)(PMe3)(dppe)}+, which dimerized in the presence of acetonitrile via C-C bond formation at the aryl group C4 positions, affording {Ru(NAr)(PMe3)(NCMe)(dppe)}2+. This suggested that there was substantial radical character in the imide π system on oxidation and that an aromatic group substituted at the 4-position might provide greater stability. The cations {Fe(NAr*)(PMe3)(dppe)}+ (Fe2a*), {Ru(NAr*)(PMe3)(dppe)}+ (Ru2a*), and Fe4a were examined by EPR spectroscopy, which suggested differences in electronic structure depending on the metal and ligand set. CASPT2 calculations on model systems for Ru2a* and Fe2a* suggested that the large differences in electronic structure are related to the energy gap between the π-antibonding HOMO and the π-bonding HOMO-1. Both the geometry of the phosphines, which is slightly different between the iron and ruthenium analogs, and the metal center seem to contribute to this energetic difference.

A complex with nitrogen single, double, and triple bonds to the same chromium atom: synthesis, structure, and reactivity.

A nitrogen-based analogue of the Schrock and Clark "yl-ene-yne" complex, W(CBu t )(CHBu t )(CH2Bu t )(dmpe), has been prepared. The new complex is the nitrido, imido, amido anion [NCr(NPh)(NPri2)2]-, which was structurally characterized with the [K(crypt-2.2.2)]+ counterion. The "Cr-N 1-2-3" complex was prepared from NCr(NHPh)(NPri2)2, which exists as this nitrido-amido tautomer, rather than the bis(imido) Cr(NH)(NPh)(NPri2)2. By selection of electrophile, the nitrido-imido salt K[NCr(NPh)(NPri2)2] can undergo reaction at either the imido or the nitrido to form unusual examples of nitrido or bis(imido) complexes.

Effective donor abilities of E-t-Bu and EPh (E = O, S, Se, Te) to a high valent transition metal.

Amido rotation in the chromium(vi), d(0)-system NCr(NPr(i)2)2X is under investigation as a method for the parameterization of ligands for their donor properties toward high valent metals. In this study, two new series were prepared and studied based on chalcogenide ligands, X = EBu(t) and EPh and where E = O, S, Se, Te; the OPh and SPh compounds were previously reported. The ligand donor parameters for these ligands correlate with the Cr-E-C angles in these chalcogenide series. In addition, it was found that NBO calculated overlaps and DFT calculated bond dissociation enthalpies correlate within X = halide-, EBu(t)- and EPh-series. All of the new complexes were characterized by X-ray diffraction.

Diastereomeric control of enantioselectivity: evidence for metal cluster catalysis.

Enantioselective hydrogenation of tiglic acid effected by diastereomers of the general formula [(µ-H)2Ru3(µ3-S)(CO)7(µ-P-P*)] (P-P* = chiral Walphos diphosphine ligand) strongly supports catalysis by intact Ru3 clusters. A catalytic mechanism involving Ru3 clusters has been established by DFT calculations.

A 4-coordinate Ru(II) imido: unusual geometry, synthesis, and reactivity.

A 4-coordinate Ru(II) imido complex, Ru(NAr)(PMe3)3 (1), can be prepared from cis-RuCl2(PMe3)4 and LiNHAr. The structure of the imido is perhaps best described as a flat-based trigonal pyramid with the imido in the equatorial plane. A possible explanation for the unusual geometry is discussed, along with some reactivity of 1.

[µ-Bis(diphenyl-phosphan-yl-κP)methane]-deca-carbonyl-tri-µ-hydrido-trirhenium(I)(3 Re-Re) dichloromethane solvate.

In the title compound, [Re(3)(µ-H)(3)(C(25)H(22)P(2))(CO)(10)]·CH(2)Cl(2), the three Re atoms form a triangle bearing ten terminal carbonyl groups and three edge-bridging hydrides. The bis-(diphenyl-phosphan-yl)methane ligand bridges two Re atoms. Neglecting the Re-Re inter-actions, each Re atom is in a slightly distorted octa-hedral coordination environment. The dichloro-methane solvent mol-ecule is disordered over two sets of sites with fixed occupancies of 0.6 and 0.4.

Mitral valve replacement in severe pulmonary arterial hypertension.

The immediate postoperative hemodynamics in 43 patients with severe pulmonary arterial hypertension who underwent mitral valve replacement between January 2000 and September 2001 were studied prospectively. The mean age was 30.6 years. There was mitral stenosis in 19 (44.1%), mitral regurgitation in 9 (20.9%), and mixed lesions in 15 (34.9%). In 36 patients (83.7%, group 1) pulmonary arterial pressure was sub-systemic, with a mean of 58.1 mm Hg and pulmonary vascular resistance of 743.4 dyne x s x cm(-5). Seven patients (16.3%, group 2) had supra-systemic pulmonary arterial pressure of 83.2 mm Hg and pulmonary vascular resistance of 1,529 dyne x s x cm(-5). Lung biopsies were taken from the right lower lobe in 24 patients. Operative mortality was 5.5% in group 1 and 28.5% in group 2. After mitral valve replacement, the pulmonary arterial pressure and vascular resistance decreased significantly in group 1. In group 2, pulmonary arterial pressure decreased significantly but pulmonary vascular resistance remained elevated. Pulmonary vascular changes did not progress beyond grade III (Heath-Edwards' classification). Mitral valve replacement is safe even in the presence of severe pulmonary arterial hypertension as long as pulmonary arterial pressures are below systemic pressures. Lung biopsy did not help in identifying patients with irreversible pulmonary arterial changes.