Pincer-ligated iridium complexes have proven to be highly effective catalysts for the dehydrogenation and transfer-dehydrogenation of al-A C H T U N G T R E N N U N G kanes. Immobilization onto a solid support offers significant potential advantages in the application of such catalysts particularly with respect to catalyst separation and recycling. We describe three approaches toward such immobilization: (i) covalent attachment to a Merrifield resin, (ii) covalent bonding to silica via a pendant alkoxysilane group, and (iii) adsorption on g-alumina (g-Al 2 O 3 ), through basic functional groups on the para-position of the pincer ligand. The simplest of these approaches, adsorption on g-Al 2 O 3 , is also found to be the most effective, yielding catalysts that are robust, recyclable, and comparable to or even more active than the corresponding species in solution. Spectroscopic evidence (NMR, IR) and studies of catalytic activity support the hypothesis that binding occurs at the para-substituent and that this has only a relatively subtle and indirect influence on catalytic behavior.

The structure of supported platinum and platinum-tin nanoparticles was investigated by Pt L(3) high-energy resolution fluorescence detected X-ray absorption spectroscopy (HERFD XAS) and resonant inelastic X-ray scattering (RIXS). The incorporation of tin decreased the ability of particles to adsorb both hydrogen and carbon monoxide due to tin enrichment on the surface. The platinum d band of platinum-tin particles was narrower and was shifted down relative to the Fermi level in comparison to platinum particles. The difference in electronic structure between pure and alloyed particles persisted after adsorption of hydrogen. The Pt-H antibonding state was clearly identified for the pure platinum particles. The strong adsorption of carbon monoxide changed the geometric structure of the PtSn particles. After carbon monoxide adsorption, the geometric structures of both systems were very similar. Room temperature adsorption of carbon monoxide affects the structure of platinum catalysts.

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Tandem dehydrogenation-olefin-metathesis catalyst systems, comprising a pincer-ligated iridium-based alkane dehydrogenation catalyst and a molybdenum-based olefin-metathesis catalyst, are reported to effect the metathesis-cyclooligomerization of cyclooctane and cyclodecane to give cycloalkanes with various carbon numbers, predominantly multiples of the substrate carbon number, and polymers.

When a pincer-ligated iridium complex with a phosphinite substituent in the para-position of the aromatic backbone is immobilized on γ-alumina, it becomes a highly effective supported catalyst for the transfer-dehydrogenation of alkanes. The nature of the interaction between the organometallic complex and the support was investigated using solid-state (31)P MAS NMR spectroscopy, solution-state (1)H and (31)P{(1)H} NMR spectroscopy, IR and GC/MS analysis of extracted reaction products. The phosphinite substituent is cleaved from the pincer ligand by its reaction with hydroxyl groups on the γ-alumina surface, resulting in covalent anchoring of the complex via the aryl ring. A similar reaction occurs on silica, allowing for ready grafting onto this support as well. A strategy for anchoring homogeneous catalysts on hydroxyl-terminated oxide supports though the selective cleavage of [POR]-containing ligand substituents is suggested.

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Analysis of variable-temperature reaction profiles, measured in an isothermal packed-bed reactor (PBR) whose temperature increases during the experiment, has the potential to yield accurate and precise kinetic parameters quickly for some heterogeneous catalysts. The method is demonstrated here for a typical supported nanoparticle catalyst, 2 wt% Pd/Al2O3, in the oxidation of H2, C3H8 and CO by O2. These reactions do not exhibit major changes in activation energy as a function of conversion over the range of reaction conditions analyzed. Reliable and quantitative information about rate laws was extracted readily from the shapes and positions of these profiles, as an alternative to more laborious conventional kinetic analyses. Temperature and pressure gradients were minimized by the use of sieved catalyst particles and large amounts of inert diluent for both the catalyst and feed gas. Curve-fitting of analytical expressions with as few as two adjustable parameters results in remarkable agreement between models and data. First-order profiles are indeed kinetically-limited, without mass and heat transfer effects, while inverse-firstorder profiles deviate from kinetically-controlled behavior at intermediate-to-high conversions. The activation energy and reaction order with respect to the limiting reactant obtained from a single reaction profile (with appropriate data truncation for non-kinetic phenomena, as necessary) are at least as accurate and precise as those obtained from a conventional Arrhenius analysis conducted with data obtained under differential conditions, and are measured in a fraction of the experimental time. Information about more elaborate rate laws can be obtained by global curve-fitting of a family of such profiles recorded with different volumetric flow rates.

O) catalyzed the transfer of hydrogen from cyclooctane to 3,3-dimethyl-1-butene to give cyclooctene and 2,2-dimethylbutane. The catalysts could be recycled. Thus, TONs of the 1st reusing runs were 1520 and 940 for respectively. After the reaction with 1/Al 2 O 3 /Na 2 O 3 , ICP-MS analysis showed that 70 ppm of Ir was leached to the solution.Comment: Iridium pincer complexes immobilized on Al 2 O 3 /Na 2 O were characterized by solid state 31 P NMR and IR spectroscopy. Their catalytic activity was superior to that of their parent iridium pincer complexes. Ir O O (t-Bu) 2 P P(t-Bu) 2 OP(t-Bu) 2 1 + 1.34 µmol Ir of 1