Holger B. Friedrich

Microwave‐Assisted Transfer Hydrogenation of Ketones by Ru(xantphos) Arene Complexes

A Ru‐catalyzed hydrogen transfer from 2‐propanol to acetophenone in the presence of the strong base KOtBu afforded 1‐phenyl alcohol in >99 % yield within 5 min under microwave irradiation; no reaction occurred in the absence of the base. A series of catalysts was then prepared in situ from [RuCl2‐η6‐p‐cymene]2 and xantphos family ligands, which were characterized by having natural bite angles ranging from 102.2 to 137.9°. The Ru(xantphos)arene catalyst was used for various substrates to give yields and turnover frequencies between 48 and 99 % and between ≥1431 and 2982 h−1, respectively, for acetophenone derivatives and >99 % and ≥2982 h−1 for sterically bulky ketones (benzophenone, 9H‐fluoren‐9‐one, and α‐tetralone).

Efficient Solvent Free Knoevenagel Condensation Over Vanadium Containing Heteropolyacid Catalysts

Various V/P mole ratios of vanadium substituted Keggin-type phosphomolybdic acids were synthesized by the hydrothermal method. These materials were characterized using several physico-chemical techniques such as X-ray diffraction, FT-IR, N2-sorption, Raman spectroscopy, 31P MAS NMR, SEM and NH3-TPD. FT-IR, Raman spectroscopy and 31P NMR results confirm the formation of the primary structure of the Keggin ion and its crystalline nature is shown clearly by XRD. NH3-TPD results reveal that the acidity of the materials systematically decreases with increasing vanadium content. The Knoevenagel reaction carried out over vanadium substituted phosphomolybdic acid with various V/P mole ratios indicate that the higher V/P mole ratio exhibits better catalytic performance under solvent free conditions. The catalytic properties correlate with the structural properties and the acidity of the materials.Graphical Abstract

Synthesis and characterization of a large bite angle iridium nixantphos complex

The complex (nixantphos)Ir(cod)Cl·CH2Cl2(0.5C7H8) 3 has been synthesized and structurally characterized by NMR, IR, and single crystal X-ray diffraction. The coordination around Ir is trigonal bipyramidal with both P groups of the nixantphos bound in a bis-equatorial mode. The bis-chelating cod (C8H12) occupies the remaining equatorial position and an axial position. This mode of bonding resulted in a large bite angle (P1—Ir—P2) of 106.49° (3) for 3. The IR and NMR data support the elucidated structure. Thermal analyses of 3 indicate that it is thermally stable up to decomposition greater than 400°C.

Synthesis, characterization, and cytotoxic and antimicrobial activities of ruthenium(II) arene complexes with N,N-bidentate ligands

Abstract Three new complexes, [(η6-C6H6)RuCl(C5H4N-2-CH=N-Ar)]PF6 (Ar = phenylmethylene (1), (4-methoxyphenyl)methylene (2), and phenylhydrazone (3)), were prepared by reacting [(η6-C6H6)Ru(μ-Cl)Cl]2 with N,N′-bidentate ligands in a 1 : 2 ratio. Full characterization of the complexes was accomplished using 1H and 13C NMR, elemental and thermal analyses, UV–vis and IR spectroscopy and single crystal X-ray structures. Single crystal structures confirmed a pseudo-octahedral three-legged, piano-stool geometry around Ru(II), with the ligand coordinated to the ruthenium(II) through two N atoms. The cytotoxicity of the mononuclear complexes was established against three human cancer cell lines and selectivity was also tested against non-cancerous human epithelial kidney (HEK 293) cells. The compounds were selective toward the tumor cells in contrast to the known anti-cancer drug 5-fluoro uracil which was not selective between the tumor cells and non-tumor cells. All the compounds showed moderate activity against MCF7 (human breast adenocarcinoma), but showed low antiproliferative activity against Caco-2 and HepG2. Also, antimicrobial activities of the complexes were tested against a panel of antimicrobial-susceptible and -resistant Gram-negative and Gram-positive bacteria. Of special interest is the anti-mycobacterial activity of all three synthesized complexes against Mycobacterium smegmatis, and bactericidal activity against resistant Enterococcus faecalis and methicillin-resistant Staphylococcus aureus ATCC 43300.

The Role of Copper Exchanged Phosphomolybdic Acid Catalyst for Knoevenagel Condensation

Cu exchanged heteropolyacid catalysts were synthesized by ion exchange method and characterized using various physico-chemical techniques such as X-ray diffraction (XRD), FT-IR, Raman, BET surface area, temperature programmed desorption (TPD) of ammonia, 31P NMR, pyridine adsorbed FT-IR spectroscopy, ICP-AES and STEM analysis. XRD diffractograms shows crystallites of heteropolyacid, while FT-IR and Raman spectra indicate that the Keggin ion is retained in the catalysts. 31P NMR, ammonia TPD and pyridine adsorbed FT-IR spectra results suggest that acidity decreases once Cu was incorporated in the heteropolyacid catalyst. For the Knoevenagel condensation reaction, the Cu exchanged phosphomolybdic acid (Cu–PMA) exhibits better catalytic performance than the phosphomolybdic acid (PMA) catalyst and this is related closely with the structural and acidic properties of the catalyst.Graphical Abstract

4,6-Bis(diphenyl­phosphino)phenoxazine (nixantphos)

The title compound, C36H27NOP2, has been reported as a ligand on rhodium for the catalysis of hydroformylation reactions. The key feature of the compound is the intramolecular P⋯P distance of 4.255 (2) Å. The bond angles at the P atoms range from 99.93 (10) to 103.02 (10)°. The phenoxazine ring system is essentially planar and a non-crystallographic mirror plane through the N⋯O vector bisects the molecule. The C—O bond lengths range from 1.388 (2) to 1.392 (2) Å and the C—N bond lengths range from 1.398 (3) to 1.403 (3) Å.

Effect of Various Au/Al2O3 Preparations on Catalytic Behaviour during the Continuous Flow Hydrogenation of an Octanal/Octene Mixture

Supported gold catalysts were prepared on a γ‐Al2O3 support by using the incipient wet impregnation and the deposition–precipitation methods. These catalysts were assessed for the continuous flow, liquid phase hydrogenation of an octanal/octene mixture, and their activity was compared with the activity of a commercially available Au/Al2O3 catalyst. These catalysts were characterised by inductively coupled plasma optical emission spectroscopy, hydrogen chemisorption, BET surface area and pore volume measurements, Raman spectroscopy, temperature‐programmed reduction of hydrogen, energy‐dispersive X‐ray spectroscopy mapping, HRTEM and powder XRD to determine gold crystallites. The results obtained revealed that gold crystallite size, dispersion and the presence of gold chloride had a significant effect on the product selectivity obtained. Large gold crystallites (particle size >15 nm) unevenly distributed on the alumina support obtained by using the wet impregnation method were inactive in hydrogenation. Hydrogen spillover resulted in the formation of protonic acid sites originating from molecular hydrogen, together with the formation of HCl‐catalysed acetal, and yielded 90 mol % selectivity towards the C24 acetal. In contrast, small gold crystallites (particle size <10 nm) evenly distributed on the alumina support obtained by using the deposition–precipitation preparation method facilitated the hydrogenation of the aldehyde and yielded 75 mol % selectivity towards the desired product, octanol.

The effect of the oxidation environment on the activity and selectivity to aromatics and octenes over cobalt molybdate in the oxidative dehydrogenation of n-octane

A cobalt molybdate catalyst was synthesised by the co-precipitation method and characterized by XRD, BET-surface area measurements, ICP-OES, Raman, TPR, TPO, SEM and SEM-EDX. XRD results showed that the dominant phase in the catalyst is the β-phase. The ratio of Co:Mo was determined by ICP-OES to be 1:1.04. The excess molybdenum is found in the molybdenum trioxide phase as shown by the Raman results. The TPR/O/R/O/R results showed that the catalyst can undergo the redox cycle where cobalt molybdate reduces to the molybdite and spinel form of cobalt molybdate (by 5% hydrogen) and oxidize back to the cobalt molybdate after oxygen exposure. The catalytic testing was carried out in a continuous flow fixed bed reactor at atmospheric pressure and a temperature range of 350 to 550 °C in 50 °C intervals with different oxygen content (i.e. C:O ratio of 8:0, 8:1, 8:2, 8:3 and 8:4) in the reaction mixture. The conversion of n-octane increased with increase in the oxygen content in the reaction mixture, which was accompanied by changes in the selectivity patterns. The dominant products were the octenes and COx at all temperatures and different carbon to oxygen ratios. Furthermore, the selectivity to aromatic products increased with increase in the strength of the oxidising environment in the feed mixture and was dominated by styrene and ethylbenzene (both products of 1,6-cyclization). The yields of octenes, aromatics, cracked products and COx at 500 °C showed that an increase in the oxygen content resulted in a decrease in the yield to octenes and an increase in what can be considered secondary products (i.e. aromatics and COx). The total selectivity percentage of value-added products (i.e. octenes and aromatics) also decreased with increase in the oxygen content, due to the increase in cracked products and COx yields (which are not considered value added products). Characterization of the spent catalysts at the different conditions showed that the catalyst maintains the cobalt molybdate phase under the 8:2, 8:3 and 8:4 C:O conditions, while complete segregation took place under dehydrogenation conditions and partial segregation occurred at an 8:1 C:O ratio.

CO oxidation activity enhancement of Ce0.95Cu0.05O2−δ induced by Pd co-substitution

A bimetallic, ionic, Ce0.93Pd0.02Cu0.05O2−δ catalyst was synthesized in one step using a urea-assisted solution combustion method. The structural and electronic properties of the catalyst were studied by different techniques together with those of mono-metallic analogues. The catalytic performance of the materials was investigated using CO oxidation as the model exhaust reaction and the nature of the active sites was examined by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). X-ray diffraction (XRD), Raman spectroscopy, XPS, XANES, EXAFS and high resolution transmission electron microscopy (HR-TEM) revealed that the prepared materials are single-phase, solid-solution oxides with a fluorite structure. In situ XRD studies showed that the prepared materials are metastable up to 1100 °C. The correlation of the characterization and catalytic results indicates that catalytic performance is influenced by the presence of oxygen vacancies and the existence of synergism between Pd2+, Cu2+ and cerium ions. DRIFTS results revealed that CO interacts with the active centres already at room temperature, forming Cu+ and Pd2+ carbonyls.

The Effects of SCILL Catalyst Modification on the Competitive Hydrogenation of 1-Octyne and 1,7-Octadiene versus 1-Octene

Competitive hydrogenation of mixtures of related unsaturated compounds remains a challenging problem. Recently, solid catalysts with an ionic liquid layer (SCILL) have shown potential for increased catalyst selectivity under batch conditions. Our results for the continuous flow competitive hydrogenation of 1‐octyne and 1,7‐octadiene versus 1‐octene with a nickel SCILL catalyst indicate improved catalyst selectivity under trickle bed conditions. Different ionic liquids ([MMIM][MeOSO3], [MMIM][OcOSO3], [MMIM][NTf2], [MePsec‐Bu3 ][MeOSO3], and [Et3S][NTf2]; MMIM=1,3‐dimethylimidazole and Tf=trifluoromethanesulfonyl) with varying catalyst loadings were investigated. The results highlight the importance of potential site‐specific interactions by the ionic liquid. They also indicate the importance of the cation for these effects.