IR pyridine

Virtually every iridium catalyst of the formula [Ir(L )(COD)] [X] for asymmetric olefin hydrogenation that has appeared after the initial counterion effect studies was based on BArp as the preferred anion [14]. The anion effect is broadly applicable in iridium-catalyzed reductions as experiments with a direct analog of the Crabtree catalyst of the formula [Ir(pyridine)(Cy3P)(COD)]BArp indicates (Fig. 2). 

The predominance of isomer 2c over 2a or 2b is consistent with Crabtree s findings, which convincingly demonstrated that in the reaction of H2 with [Ir(pyridine) (PR3)(COD)]PFg, the formation of an Ir-H bond trans to the N ligand is electronically favored [23]. Highly selective formation of isomer 2c results from H2 addition to the... 

While the versatility is well accepted, one should be cautious in practicing this approach. The lack of additivity of w and log F values has been found in molecules where intramolecular interactions are not negligible (51, 52, 53). The log F values of / -pyridylmethyldialkylamines have been determined as shown in Table I (52). The values calculated on the basis of Xw, ir(pyridine) = 0.65, tt(-CH2-) = 0.5 and 7r[N(CH3)2] = —0.35, are quite different from the corresponding experimental values. The lack of additivity should indicate peculiar intramolecular interactions depending upon the side chain structure. In such cases, it is essential to use the experimental log F values for structure-activity correlations. 

The acidity of the catalysts used here has been determined previously by IR pyridine adsorption experiments [5]. The amounts of acid sites (Bronsted/Lewis) at 300°C (mmol/g) are LaHY (0.133/0.089) and MSA (0.026/0.099). The total acidity found by IR is less than (< 1/20) the actual number of A1 present, not all A1 sites are accessible to pyridine. 

The hydrothermal deactivation of Y zeolite containing 0, 4, 7 and 12 wt.% of REO and its effects on catalytic activity, stability and selectivity were investigated. The Y zeolites were hydrothermally deactivated at 788°C in three consecutive cycles of two hours each. The fresh and deactivated zeolites were characterized by measuring Unit Cell Size (UCS) and surface area. The acidic properties were measured by the Temperature Programmed Desorption (TPD) of ammonia and IR-pyridine desorption. In order to correlate structural, textural and acid properties with catalytic behavior, the zeolites were evaluated in the conversion of cyclohexane. The Hydrogen Transfer Index (HTI) measured as a ratio of paraffins to olefins is a parameter of the selectivity. It was found that the REO was incorporated into zeolite structure up to high concentrations modifying to some extent XRD deflection, the acidic properties and the HTI ratio. After deactivation, the acidity and HTI were diminished and the Lewis/Bronsted acid ratio was modified. HTI decreased as REO concentration increased. 

The powder X-ray diffraction patterns were measured in a D-500 SIEMENS diffractometer with a graphite seeondary beam monochromator and CuKoj contribution was eliminated by the DIFFRAC/AT software to obtain a monochromatic CuKa,. The Unit Cell Size (UCS) was measured following the ASTM D-3942-90 procedure. The Surface areas were measured by nitrogen adsorption at 75 K on a Micromeritics Accusorb 2100 E equipment using the ASTM method D-3663-78. Temperature Programmed Desorption (TPD) of ammonia and pyridine adsorption by Infrared Spectroscopy (IR) were used to characterize the acidity of the zeolites. For IR-Pyridine the spectra were recorded each 100°C and the characteristic bands of Lewis and Bronsted acid sites (1444 cm" and 1540 cm, respectively) were integrated in order to obtain the total acid sites. 

Martin et al. [429] used the IR/pyridine technique (cf. Sect. 5.5.2.6.2) to look at the elimination of Bronsted acid centers upon hydrothermal treatment of H-ZSM-5 zeolite and evidenced the condensation of extra-framework Al-containing species (Lewis sites). 

Bronsted and Lewis acidity of ZSM-5 zeolites loaded with transition metal ions (Co, Fe) via impregnation were investigated by Rhee et al. [682-684] using the IR/pyridine adsorption technique with thin sample wafers. 

IR pyridine adsorption studies show that the AL-PILC sample Vc calcined at 680°C (Vc-680) has a strong Lewis acidity only (Fig.4). On this sample steamed at 550°C (Fig.5) a strong Bronsted acidity is observed still detectable after evacuation at 480°C. Steaming at 650°C reduces the strength of both Brdnsted and Lewis acid sites,no more detectable after degassing at 300°C. 

COMPARISON BETWEEN ir NET CHARGES OF NITROGEN AND CARBON ATOMS IN THE a- AND p-POSITIONS IN PYRIDINE AND THIAZOLE (PPP-ir METHOD)... 

Oxazolo[4,5-6]pyridin-2(3 H)-one IR, 6, 653 <76HCA1593) Oxazolo[4,5-fi]pyridin-2(3H)-one, 3-(4-chlorophenyl)-3a,7a-dihydro-6-methyl-X-ray, 6, 647 <79CPB2261) Oxazolo[4,5-6]pyridin-2(3H)-one, 3-(4-chlorophenyl)-3a,7a-dihydro-7a-methyl-X-ray, 6, 647 <79CPB2261) 5H-Oxazolo[3,2-a]pyridin-3(2H)-one, 2-phenyl-6,7,8,8a-tetrahydro-X-ray, 6, 646 <77MI42902) Oxazolo[5,4-d]pyrimidin-4-amine, A7-methyl- H NMR, 6, 650 <70BCJ3909)... 

Pyrazolo[4,3-c]pyridine, 2-benzyl- H NMR, 5, 308 <73X441) Pyrazolo[3,4-b]pyridin-3-one, 6-metbyl-4-pbenyl-IR, 5, 332 <69M1250)... 

Pyridine, 2-cyano-IR, 2, 130 <78JPC1268> kinetic data, 2, 298 <66CJCI765> microwave, 2, 104 <75JSP(58)178)... 

Pyridine, 2-dimethylamino-IR,2, 130 <78JPC1268> rate constants, 2, 190 (75JCS(P2)1600)... 

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