Fundamental Structural and Electronic Understanding of Palladium Catalysts on Nitride and Oxide Supports.

The nature of the support can fundamentally affect the function of a heterogeneous catalyst. For the novel type of isolated metal atom catalysts, sometimes referred to as single-atom catalysts, systematic correlations are still rare. Here, we report a general finding that Pd on nitride supports (non-metal and metal nitride) features a higher oxidation state compared to that on oxide supports (non-metal and metal oxide). Through thorough oxidation state investigations by X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), CO-DRIFTS, and density functional theory (DFT) coupled with Bader charge analysis, it is found that Pd atoms prefer to interact with surface hydroxyl group to form a Pd(OH)x species on oxide supports, while on nitride supports, Pd atoms incorporate into the surface structure in the form of Pd-N bonds. Moreover, a correlation was built between the formal oxidation state and computational Bader charge, based on the periodic trend in electronegativity.

A high-purity gas-solid photoreactor for reliable and reproducible photocatalytic CO2 reduction measurements.

Reactions between a gas phase and a solid material are of high importance in the study of alternative ways for energy conversion utilizing otherwise useless carbon dioxide (CO2). The photocatalytic CO2 reduction to hydrocarbon fuels like e.g., methane (CH4) is such a potential candidate process converting solar light into molecular bonds. In this work, the design, construction, and operation of a high-purity gas-solid photoreactor is described. The design aims at eliminating any unwanted carbon-containing impurities and leak points, ensuring the collection of reliable and reproducible data in photocatalytic CO2 reduction measurements. Apart from the hardware design, a detailed experimental procedure including gas analysis is presented, allowing newcomers in the field of gas-solid CO2 reduction to learn the essential basics and valuable tricks. By performing extensive blank measurements (with/without sample and/or light) the true performance of photocatalytic materials can be monitored, leading to the identification of trends and the proposal of possible mechanisms in CO2 photoreduction. The reproducibility of measurements between different versions of the here presented reactor on the ppm level is evidenced.

Tri-tert-butyl-phospho-nium hy-droxy-tris-(penta-fluoro-phen-yl)borate.

The ionic title compound, C(12)H(28)P(+)·C(18)HBF(15)O(-), was obtained by the stoichiometric reaction of (t)Bu(3)P, B(C(6)F(5))(3) and water in toluene. A weak P-H⋯O hydrogen bond is observed in the crystal structure.

2-Vinyl-pyridine-tris-(penta-fluoro-phen-yl)borane hexane monosolvate.

The title compound, C(7)H(7)N·B(C(6)F(5))(3)·C(6)H(14), was obtained by the stoichiometric reaction of 2-vinyl-pyridine and tris-(penta-fluoro-phen-yl)borane in toluene. The formed adduct exhibits a restricted rotation along the B-N bond resulting in an asymmetry, which can be also observed in the (19)F NMR spectra. The B-N distance is equivalent to the distances found for 2-methyl-pyridine and 2-ethyl-pyridine B(C(6)F(5))(3) adducts. For the final refinement, the contributions of disordered solvent mol-ecules were removed from the diffraction data with SQUEEZE in PLATON [van der Sluis & Spek (1990). Acta Cryst. A46, 194-201; Spek (2009). Acta Cryst. D65, 148-155].

Titanocene(III) complexes with 2-phosphinoaryloxide ligands for the catalytic dehydrogenation of dimethylamine borane.

A study of the dehydrogenation of dimethylamine borane using different titanocene(III) complexes with 2-phosphinoaryloxide ligands is presented. Complexes Cp2Ti(κ(2)-O, P-O-C6H4-PR2) (3a: R = i-Pr, 3b: R = Ph) (Cp = η(5)-cyclopentadienyl) and Cp*2Ti(κ(1)-O-O-C6H4-PR2) (5a: R = i-Pr, 5b: R = Ph) (Cp* = η(5)-pentamethylcyclopentadienyl) were prepared by reactions of the 2-phosphinophenol ligand with different titanocene sources and fully characterised. Their catalytic activity depends on the steric influence of the cyclopentadienyl ligand, the coordination mode of the 2-phosphinoaryloxide ligand and on the used solvent. Complex 3a showed a turnover number of 43.2 in the neat substrate after 24 hours. EPR investigations were used to elucidate the fate of the Ti(III) catalyst.

Group 4 metallocene catalysed full dehydrogenation of hydrazine borane.

A study of the full dehydrogenation of hydrazine borane (H2N-NH2·BH3) to give H2 and N2 as gaseous products catalysed by a variety of group 4 metallocene alkyne complexes of the type CpM(L)(η(2)-Me3SiC2SiMe3) (Cp' = substituted or unsubstituted η(5)-cyclopentadienyl; M = Ti, no L; M = Zr, L = pyridine) and group 4 metallocene hydrides is presented. Volumetric data show that the amount of hydrogen released is strongly dependent on both, the metal and the cyclopentadienyl ligand.

Investigation and enhancement of the stability and performance of water reduction systems based on cyclometalated iridium(III) complexes.

Water reduction systems that use a bis-cyclometalated Ir(III) photosensitiser (PS) along with homogeneous Pd complexes as a source of in-situ-formed colloidal Pd as the water reducing complex (WRC) and triethylamine (TEA) as the sacrificial electron donor were tested and characterised with respect to their photocatalytic H(2) production performance. It was confirmed that substitution of the 2-(pyridin-2-yl)benzen-1-ide (pyb) ligand in the well-known system [Ir(pyb)(2)(bpy)](+) (bpy=2,2'-bipyridine) by the fluorinated cyclometalating ligand 5-fluoro-2-(5-methylpyridin-2-yl)benzen-1-ide (Fmpyb) tremendously enhanced the H(2) production rate. Moreover, variation of the bidentate N^N ligand bpy by alkyl substitution in the 4,4'-position resulted in an increase in the H(2) production yield by a factor of three. The incident-photon-to-hydrogen-efficiency could be enhanced from 2.6 to 12.3%. Furthermore, a new dinuclear Co complex was used as a reduction catalyst and showed up to 760 turnovers after 20 h. A detailed study of the concentration impact of all components in the photoredox system was performed. DFT calculations were used to aid the explanation of the findings.

An intermolecular heterobimetallic system for photocatalytic water reduction.

Teamwork: A new intermolecular heterobimetallic system for photocatalytic water reduction, consisting of a photosensitizer of the type [Ru(bpy)(2)(L)](PF(6))(2) (L=bidentate ligand), a dichloro palladium complex PdCl(2)(L) serving as the water reduction catalyst, and triethyl amine as electron donor, is presented. Variations of the ligand as well as of the palladium source results in a significant improvement of the performance of the catalyst system.

Catalytic dehydrogenation of dimethylamine borane by group 4 metallocene alkyne complexes and homoleptic amido compounds.

Dehydrogenation of Me(2)NH·BH(3) (1) by group 4 metallocene alkyne complexes of the type Cp(2)M(L)(η(2)-Me(3)SiC(2)SiMe(3)) [Cp = η(5)-cyclopentadienyl; M = Ti, no L (2Ti); M = Zr, L = pyridine (2Zr)] and group 4 metal amido complexes of the type M(NMe(2))(4) [M = Ti (8Ti), Zr (8Zr)] is presented.