Imidazolium ion tethered TsDPENs as efficient water-soluble ligands for rhodium catalyzed asymmetric transfer hydrogenation of aromatic ketones

An imidazolium ion tethered TsDPEN has been synthesized readily and used as a water-soluble ligand for [Cp*RhCl₂]₂ catalyzed asymmetric transfer hydrogenation (ATH) of aromatic ketones in water. This process provided the secondary alcohols in moderate to excellent conversions (up to 100%) with high enantioselectivities (up to 98% ee) under mild reaction conditions without adding any surfactants. The catalytic system is highly effective with the substrate to catalyst (S/C) ratio of 500 and low hydride donor loading of 1.5 equiv. of HCO₂Na. The procedure presented is simple and makes this method suitable for practical use.     

Asymmetric Transfer Hydrogenation of Ketones Using New Iron(II) (P-NH-N-P′) Catalysts: Changing the Steric and Electronic Properties at Phosphorus P′

The asymmetric transfer hydrogenation (ATH) of ketones is an efficient method for producing enantio-enriched alcohols which are used as intermediates in a variety of industrial processes. Here we report the synthesis of new iron ATH precatalysts (S,S)-[FeBr(CO)(Ph₂PCH₂CH₂NHCHPhCHPhNC=CHCH₂PR′₂)][BPh₄] (R′=Et, and ortho-tolyl (o-Tol)) where one of the phosphine groups is modified with small alkyl and large aryl substituents to probe the effect of this change on the activity and selectivity of the catalytic system. A simple reversible equilibrium kinetic model is used to obtain the initial TOF and the inherent enantioselectivity S=k_R/k_S of these catalysts along with those for the previously reported catalysts with R′=Ph and Cy for the ATH of acetophenone. With an increase in the size of the PR′₂ group, the TOF goes through a maximum at PPh₂ while the S value goes through a maximum of 510 at R′=Cy. The complex with R′=o-Tol starts with a high S value of 200 but is rapidly changed to a second catalyst with an S value of 28. For the reduction of acetophenone to (R)-1-phenylethanol, turnover numbers of up to 5200 and ee up to 98 % were achieved. The chemotherapeutic pharmaceutical precursor (R)-(3′,5′-bis(trifluoromethyl))-1-phenylethanol is synthesized in up to 95 % ee. Several other alcohols can be prepared in greater than 90 % ee by choosing the precatalyst with the correctly matched steric properties. A hydride complex derived from the catalyst with R′=Cy is characterized by NMR spectroscopy. It is proposed that low concentration trans-hydride carbonyl complexes with the FeH parallel to the NH of the ligand are the active catalysts in all of these systems.     

An Alternative Synthesis of [Pd2Cl2(μ-dmpm)2]

A new, high yield synthesis of [Pd₂Cl₂(m̈-dmpm)₂] (dmpm = bis(dimethylphosphino)methane), which avoids the use of the ill-defined, polymeric substance [PdCl(CO)]_n as a starting material, is described. The procedure involves ligand metathesis of [Pd₂Cl₂(m̈-dppm)₂] (dppm = bis(diphenylphosphino) methane) with dmpm using a solvent in which both [Pd₂Cl₂(m̈-dppm)₂] and [Pd₂Cl₂(m̈-dmpm)2] are only sparingly soluble. Yields of > 98% are routinely obtained.     

Di-μ-hydroxy macrocyclic ytterbium(III) complex

The mononuclear [YbracL]Cl₃·2H₂O and dinuclear [Yb₂(OH)₂Cl₂(racL)₂]Cl₂·4CH₃OH·2H₂O complexes of the macrocyclic ligand L derived from trans-1,2-diaminocyclohexane and 2,6-diformylpyridine have been obtained. The formation of the dinuclear species upon addition of hydroxide to the [YbracL]Cl₃·2H₂O or the enantiopure [YbrrrrL(NO₃)₂](NO₃) has been followed using ¹H NMR spectroscopy. The X-ray crystal structure of [Yb₂(OH)₂Cl₂(racL)₂]Cl₂·4CH₃OH·2H₂O complex has been determined. The complex is a dimer consisting of two macrocyclic units. The Yb(III) ion is coordinated by six nitrogen atoms of the macrocyclic ligand, two bridging OH groups and chloride anions. The chiral macrocycle L in this complex exhibits twist-bent conformation of approximate C₂ symmetry.     

Isomerization of n-heptane on Pt/MOR/Al2O3 catalysts

Pt/MOR/Al₂O₃ catalysts with mordenite zeolite contents of 10 to 50 wt % are prepared. Solutions of H₂PtCl₆ and [Pt(NH₃)₄]Cl₂ are used as precursors of Pt. It is shown by means of transmission electron microscopy (TEM) that the localization of platinum on a MOR/Al₂O₃ mixed support depends directly on the nature of the metal’s precursor. The catalysts are tested in the isomerization of n-heptane. It is shown that the best samples of catalysts provide yields of the target products (dimethyl and trimethyl substituted isomers of heptanes) on the level of 21 wt % at a temperature of 280°C, while those of a C₅₊ stable catalyzate are on the level of 79–82 wt %. The catalysts can be used to improve the environmental friendliness of gasolines by employing them in the isomerization of the 70–105°C fraction of directly distilled gasoline.     

Ruthenium catalyzed asymmetric transfer hydrogenation based on chiral P,N,O Schiff base ligands and crystal structure of a ruthenium(II) complex bearing chiral P,N,O Schiff base ligands

A ruthenium catalyst, generated in situ by heating the chiral P,N,O Schiff base ligand L (L = (S)-Ph₂PC₆H₄CNCHPhCH₂OH) with Ru(DMSO)₄Cl₂ in 2-propanol, is active for asymmetric transfer hydrogenation with best enantioselectivity up to 81%. A ruthenium complex of formula RuL₂Cl₂ is prepared and its crystal structure revealed that the two chiral P,N,O Schiff ligands are in meridional configuration. This complex is also an active catalyst for asymmetric transfer hydrogenation. However, the ‘[Ru(DMSO)₄]Cl₂ + chiral P,N,O ligand’ protocol displays better enantioselectivity.     

Oxidation of Benzene Catalyzed by 2,2′-Bipyridine and 1,10-Phenantroline Cu(II) Complexes

The use of mononuclear Cu(II) 2,2′-bipyridine and 1,10-phenantroline complexes as catalysts in the oxidation of benzene, using hydrogen peroxide and tert-butyl hydroperoxide as oxidant in CH₃CN/H₂O solution is presented. The reactions were carried out at 25 and at 50 °C. The complexes [Cu(bipy)₃]Cl₂ · 6H₂O (1), [Cu(bipy)₂Cl]Cl · 5H₂O (2), [Cu(bipy)Cl₂] (3), [Cu(phen)₃]Cl₂ · 7H₂O (4), [Cu(phen)₂Cl]Cl · 5H₂O (5), [Cu(phen)Cl₂] (6) were able to oxidize benzene into phenol, hydroquinone and p-benzoquinone. Highest conversion (22%) was obtained using [Cu(Phen)Cl₂] (6) as catalyst.     

Cyclohexane oxidation catalyzed by 2,2′-bipyridil Cu(II) complexes

In this work we present the use of three mononuclear Cu(II) complexes containing the ligand 2,2′-bipyridil as catalyst in the cyclohexane oxidation, using hydrogen peroxide and tert-butyl hydroperoxide as oxidant. The reactions were carried out in acetonitrile–H₂O at room temperature and at 50 °C. The complexes [Cu(bipy)₃]Cl₂, [Cu(bipy)₂Cl]Cl, [Cu(bipy)Cl₂] were able to oxidize cyclohexane into cyclohexanol, cyclohexanone and cyclohexyl hydroperoxide. Yields up to 43.7% were obtained for the system [Cu(bipy)Cl₂]/H₂O₂.     

Unsaturated Copolyesters from Macrolactone/Norbornene: Toward Reaction Kinetics of Metathesis Copolymerization Using Ruthenium Carbene Catalysts

Unsaturated copolyesters are of great interest in polymer science due to their broad potential applications and sustainability. Copolyesters were synthesized from the ring-opening metathesis copolymerization of ω-6-hexadecenlactone (HDL) and norbornene (NB) using ruthenium-alkylidene [Ru(Cl₂)(=CHPh)(1,3-bis(2,4,6-trimethylphenyl)-2-imidazolidinylidene)(PCy₃)] (Ru1), [Ru(Cl)₂(=CHPh)(PCy₃)₂] (Ru2), and ruthenium-vinylidene [RuCl₂(=C=CH(p-C₆H₄CF₃))(PCy₃)₂] (Ru3) catalysts, respectively, yielding HDL-NB copolymers with different ratios of the monomer HDL in the feed. The activity of N-heterocyclic-carbene (NHC) (Ru1) and phosphine (Ru2 and Ru3) ligands containing ruthenium-carbene catalysts were evaluated in the synthesis of copolymer HDL-NB. The catalysts Ru1 with an NHC ligand showed superior activity and stability over catalysts Ru2 and Ru3 bearing PCy₃ ligands. The incorporation of the monomers in the copolymers determined by ¹H-NMR spectroscopy was similar to that of the HDL-NB values in the feed. Experiments, at distinct monomer molar ratios, were carried out using the catalysts Ru1–Ru3 to determine the copolymerization reactivity constants by applying the Mayo–Lewis and Fineman–Ross methods. The copolymer distribution under equilibrium conditions was studied by the ¹³C NMR spectra, indicating that the copolymer HDL-NB is a gradient copolymer. The main factor determining the decrease in melting temperature is the inclusion of norbornene units, indicating that the PNB units permeate trough the HDL chains. The copolymers with different molar ratios [HDL]/[NB] have good thermal stability up to 411 °C in comparison with the homopolymer PHDL (384 °C). Further, the stress–strain measurements in tension for these copolymers depicted the appreciable increment in stress values as the NB content increases.     

Synthesis and structural characterization of a new polynuclear heteroselenometallic cluster with asymmetric coordination of palladium(I) atoms

Treatment of [Et₄N]₂[WSe₄] with [Pd₂(μ-dppm)₂Cl₂] in CH₂Cl₂–DMF afforded a novel polynuclear heteroselenometallic palladium(I) cluster [(μ₃-WSe₄)₂(Pd₂)₂(μ-dppm)₂]·2DMF. Its crystal structure revealed that all the palladium atoms are asymmetrically tetra-coordinated with a distorted square-planar geometry. The luminescent behavior of the cluster has been investigated.     

Cu(II) bipyridine and phenantroline complexes: Tailor-made catalysts for the selective oxidation of tetralin

Mononuclear Cu(II) complexes have been synthesized, and their structure thoroughly characterized by electrospray ionization mass spectrometry (ESI-MS). These 2,2′-bipyridine and 1,10-phenantroline mononuclear Cu(II) complexes have been tested as catalysts in the partial oxidation of tetralin (1,2,3,4-tetrahydronaphthalene), using hydrogen peroxide as oxidant in acetonitrile/water as solvent.The complexes [Cu(bipy)₃]Cl₂·6H₂O (1), [Cu(bipy)₂Cl]Cl·5H₂O (2), [Cu(bipy)Cl₂] (3), [Cu(phen)₃]Cl₂·6H₂O (4), [Cu(phen)₂Cl]Cl·5H₂O (5), [Cu(phen)Cl₂] (6) were able to oxidize tetralin at room temperature, at high degrees of conversion (62.1% with 2) into α-tetralol and α-tetralon at 91% selectivity (81% in 1-tetralon).Depending on nature and number of ligands (bipyridine or phenantroline) surrounding Cu²⁺ cation, one was able to tailor both the activity toward tetralin oxidation, and the selectivity toward 1-tetralol and 1-tetralone products, but also to raise the yield in valuable α-tetralone.     

Synthesis,characterization, and catalytic applications of Ru(III) complexes containing N-[di(alkyl/aryl)carbamothioyl]benzamide derivatives and triphenylphosphine/triphenylarsine

Six coordinated ruthenium(III) complexes of the type [RuX₂(L)(PPh₃)₂] or [RuX₂(L)(AsPh₃)₂] {where L = N-[di(alkyl/aryl)carbamothioyl]benzamide derivatives, X = Cl or Br} have been prepared by the reaction between [RuX₃(PPh₃)₃] or [RuX₃(AsPh₃)₃] (where X = Cl or Br) and N-[di(alkyl/aryl)carbamothioyl]benzamide derivatives in toluene and characterized by elemental analysis, spectral data (electronic, IR and EPR) and magnetic moment studies. The complexes act as efficient catalysts for the oxidation of alcohols in presence of N-methylmorpholine-N-oxide as oxidant at room temperature.     

Aqueous Asymmetric Mukaiyama Aldol Reaction Catalyzed by Chiral Gallium Lewis Acid with Trost‐Type Semi‐Crown Ligands

The combination of Ga(OTf)₃ with chiral semi‐crown ligands ( 1a – e ) generates highly effective chiral gallium Lewis acid catalysts for aqueous asymmetric aldol reactions of aromatic silyl enol ethers with aldehydes. A ligand‐acceleration effect was observed. Water is essential for obtaining high diastereoselectivity and enantioselectivity. The p‐phenyl substituent in aromatic silyl enol ether ( 2 h ) plays an important role and increases the enantioselectivity up to 95% ee. Although aliphatic silyl enol ethers provided low enantioselectivities and silylketene acetal is easily hydrolyzed in aqueous alcohol, the aldol reactions of silylketene thioacetal ( 12 ) with aldehydes in the presence of gallium‐Lewis acid catalysts give the β‐hydroxy thioester with reasonable yields and high diastereo‐ (up to 99 : 1) and enantioselectivities (up to 96% ee).     

Pitting of nickel during anodic galvanostatic charging in Na2SO4 solutions

The anodic galvanostatic charging technique has been used to study the pitting of nickel in acid and neutral Na₂SO₄ solutions containing various concentrations of Cl^?. Pit initiation is indicated by a change in potential in the cathodic direction, this potential being substantially higher than that required to sustain pitting. The steady-state pitting potentials are in the passive, rather than the active, potential region, a result which can be explained by the highly localized nature of the pitting process. Increasing the [Cl^?] lowers the potential for pit initiation as well as the steady-state pitting potentials. The influence of anodic charging rate (i^g_a) on pit initiation depends on the [Cl^?] in solution; at high [Cl^?] the charging curves are similar except for the potential shift with i^g_a, while at low [Cl^?] pit initiation is more difficult with higher values of i^g_a. The minimum [Cl^?] required for pit initiation increases with decreasing solution temperature, ie with decreasing solution aggressiveness. The potential for pit initiation tends to be higher at lower solution temperatures and/or at higher pH's [Cl^?], anodic charging rate, solution temperature and pH influence pit initiation by affecting the efficiency of oxide repair at local breakdown sites in the passive oxide film.     

Nickel complexes bearing 2-(1H-benzo[d]imidazol-2-yl)-N-benzylidenequinolin-8-amines: Synthesis,structure and catalytic ethylene oligomerization

A series of 2-(1H-benzo[d]imidazol-2-yl)-N-benzylidenequinolin-8-amines was synthesized and characterized. They are stable as solids while displaying a tendency to decompose in solution. On reaction with NiCl₂, different coordination pattern sets of L·NiCl₂ or [L₂Ni]²⁺·2Cl⁻ are obtainable in THF or ethanol. When activated by Et₂AlCl, the complexes L·NiCl₂ exhibit good to high catalytic activities and selectivities for 1-C₄ in ethylene oligomerization, while the complexes [L2Ni]²⁺·2Cl⁻ hardly showed any activity, which is attributable to nickel coordination by two ligands barring interaction of ethylene with the metal center.     

Preparation of microgel-supported chiral catalysts and their application in the asymmetric hydrogenation of aromatic ketones

An enantiomerically pure chiral monomer (S,S)-2 was prepared and copolymerized with styrene and four different cross-linkers to produce four distinct microgel-supported chiral TsDPEN derivatives. These chiral copolymers were allowed to form complexes with [RuCl₂(cymene)]₂ and the resulting homogeneous catalysts were applied in asymmetric hydrogenation reactions of aromatic ketones to give enantioenriched secondary alcohols in quantitative yield. These polymeric catalysts can be easily separated from the reaction mixture and recycled several times without a significant loss in catalytic activity.     

Twisted dinuclear Pd(II) complex with an exo-hexadentate ligand bearing bipyridine and carbamoly groups: Synthesis and structure

Dinuclear Pd(II) compound, [Pd₂(PMCB²⁻)Cl₂] · CH₂Cl₂ (1), has been prepared by the reaction of K₂[PdCl₄] with exo-hexadentate ligand having amide groups (3,3′-bis[N-(2-pyridylmethyl)carbamoly]-2,2′-bipyridine, H₂PMCB) in H₂O/CH₂Cl₂. X-ray crystal structure of 1 indicates that one PMCB²⁻ ligand binds two Pd(II) ions each having a distorted square planar structure. The bipyridine group of the PMCB²⁻ ligand is involved in offset face-to-face π–π interactions, which gives rise to a 1D chain. The 1D chains are linked together via the C–H⋯O hydrogen bondings between a carbon atom of pyridine group and the oxygen of carbamoly group to generate a 2D network. Between the 2D networks there exist the herringbone π–π stackings, which results in a 3D supramolecular structure.     

Selective catalytic hydrogenations in a microfluidics-based high throughput flow reactor on ion-exchange supported transition metal complexes: A modular approach to the heterogenization of soluble complex catalysts

Water-soluble ruthenium(II) and rhodium(I) complexes containing monosulfonated triphenylphosphine (mtppms) ligands were immobilized on commercially available anion-exchangers. The resulting solid catalysts were suitable for use in a microfluidics-based flow reactor (H-Cube™) of high throughput capability. With the heterogenized [{RuCl₂(mtppms)₂}₂] disubstituted alkynes were hydrogenated to cis-alkenes with up to 85% selectivity, while the use of the immobilized [RhCl(mtppms)₃] yielded 1,2-diphenylethane as the major product. The ruthenium catalyst also reduced trans-cinnamaldehyde to 3-phenylpropanal selectively and catalyzed the isomerization of 1-octen-3-ol to octan-3-one. This simple and versatile method of the immobilization of water-soluble complexes yields active and durable molecularly dispersed yet solid catalysts.     

Effect of the zeolite modulus of Pt/MOR/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts on the <Emphasis Type="Italic">n</Emphasis>-heptane isomerization reaction

The effect of the mordenite acidic modulus (SiO₂/Al₂O₃, 20 and 30) of Pt/MOR/Al2O3 catalysts on the heptane isomerization reaction is investigated. The content of zeolite in the catalysts is varied from 10 to 50 wt %, with platinum applied to the samples from solutions of different precursors: H₂PtCl₆ and [Pt(NH₃)₄]Cl₂. It is established via the TPD of ammonia and FTIR spectroscopy (the adsorption of NH₃ and СО) that the total acidity of zeolite falls as the modulus grows: the number of Brønsted (BAC) and Lewis (LAC) acidic sites is reduced, accompanied by an increase in the strength of their acidity. The catalysts are tested in the n-heptane isomerization reaction. It is shown that the selectivity of n-heptane isomerization falls substantially when the acidic mordenite modulus is increased from 20 to 30.     

Preparation of supported PtRu/C electrocatalyst for direct methanol fuel cells

In this work, high-surface supported PtRu/C were prepared with Ru(NO)(NO₃)₃ and [Pt(H₂NCH₂CH₂NH₂)₂]Cl₂ as the precursors and hydrogen as a reducing agent. XRD and TEM analyses showed that the PtRu/C catalysts with different loadings possessed small and homogeneous metal particles. Even at high metal loading (40 wt.% Pt, 20 wt.% Ru) the mean metal particle size is less than 4 nm. Meanwhile, the calculated Pt crystalline lattice parameter and Pt (2 2 0) peak position indicated that the geometric structure of Pt was modified by Ru atoms. Among the prepared catalysts, the lattice parameter of 40-20 wt.% PtRu/C contract most. Cyclic voltammetry (CV), chronoamperometry (CA), CO stripping and single direct methanol fuel cell tests jointly suggested that the 40-20 wt.% PtRu/C catalyst has the highest electrochemical activity for methanol oxidation.