Pincer catalyst

Another recent patent (22) and related patent application (31) cover incorporation and use of many active metals into Si-TUD-1. Some active materials were incorporated simultaneously (e.g., NiW, NiMo, and Ga/Zn/Sn). The various catalysts have been used for many organic reactions [TUD-1 variants are shown in brackets] Alkylation of naphthalene with 1-hexadecene [Al-Si] Friedel-Crafts benzylation of benzene [Fe-Si, Ga-Si, Sn-Si and Ti-Si, see apphcation 2 above] oligomerization of 1-decene [Al-Si] selective oxidation of ethylbenzene to acetophenone [Cr-Si, Mo-Si] and selective oxidation of cyclohexanol to cyclohexanone [Mo-Si], A dehydrogenation process (32) has been described using an immobilized pincer catalyst on a TUD-1 substrate. Previously these catalysts were homogeneous, which often caused problems in separation and recycle. Several other reactions were described, including acylation, hydrogenation, and ammoxidation. 

Van Koten et al. reported on a negative dendritic effect in the Kharasch addition reaction. [3 9,40] A fast deactivation for the carbosilane dendrimer supported NCN pincer catalyst (Figures 4.28 and 4.29) was observed by comparison with a mononuclear analogue. This deactivation is expected to be caused by irreversible formation of inactive Ni(III) sites on the periphery of these dendrimers. 

To examine the differences in reactivity of various immobilized palladium pincer catalysts, small molecule, polymer-supported (poly(norbomene) - soluble, and Merrifield resin - insoluble), and silica-supported (SBA-15) pincer complexes were synthesized (Fig. 20.9) [44 6]. Both sulfur-containing (SCS) and phosphorous-containing (PCP) ligands were studied. 

Determined that -20% conversion of cycloalkanes to arenas can be achieved with the iridium arsino pincer catalyst than is obtained with the analogous phosphino catalyst. 

We have found that the higher levels of conversion of cycloalkanes to arenes can be achieved with the iridium arsino pincer complex, IrH2(C5H3-2,6-(CH2AsBu 2)2) than are obtained with the analogous phosphino catalyst. However, inhibition of the arsino pincer catalyst is observed at the -20% dehydrogenation level for methylcyclohexane, decalin, and dicyclohexyl. 

Aliphatic sulfonimines also reacted smoothly, but the stereoselectivity with 19a was poor. Variation of the pincer complex catalyst did not change the stereoselectivity (cf. entries 6 and 7). The reaction did not proceed while using commonly used (non-pincer) catalysts [43]. 

Mechanistic studies performed with Freeh s pincer catalyst in the Heck reaction excluded catalytic cycles with the involvement of homogeneous palladium(O) species, as indicated by the results obtained from the (recently developed) dibenzyl-test, which is directly applicable under the reactions conditions applied [24aj. Dibenzyl formation was - in contrast to Heck reactions catalyzed by palladium(O) complexes of type [Pd(PR3)2, where Pd /Pd" cycles are operative - not detectable by gas chromatography-mass spectrometry (GC/MS) when reaction mixtures of aryl bromide, olefin, benzyl chloride ( 10 mol% relative to aryl bromide), catalyst, and base were thermally treated. On the other hand, experimental observations, such as quantitative poisoning experiments with metallic mercury and CS2, which were shown to eflfidently inhibit catalysis, as well as analysis of the reaction profiles showed sigmoidal-shaped kinetics with induction periods and hence indicated that palladium nanoparticles are the catalytically active form... 

The completely saturated skeleton of carbazole 289 was used as a platform to investigate and develop selective iridium-catalyzed dehydrogenation reactions for the synthesis of net pyrroles bearing fused carbocyclic ring systems 290. Thus, complete reduction of the carbazole 288 skeleton with Pd/C at 120 °C followed by reaction with an iridium pincer catalyst underwent dehydrogenation in smooth order. These molecules were shown to have an activity window of 172-178 °C (14CC5987). 

The design and catalytic activity of dibenzobarrelene-based bifunctional PC(5p )P pincer catalysts for acceptor-less dehydrogenation of primary and secondary alcohols to give carbonylic and carboxylic compounds has been described. The mechanism of the H2 formation involves intra-molecular cooperation between the structurally remote functionality and the metal centre. The feasibility of the complete catalytic cycle was studied using a stoichiometric model. ... 

Alkane Metathesis Using Ir-Pincer Catalysts and Olefin Metathesis In 2006, Goldman, Brookhart, and coworkers [18, 19] reported a modified, tandem w-alkane metathesis reaction employing PCP iridium pincer catalysts (dehydrogena-tion/hydrogenation) with an olefin metathesis catalyst (Figure 2.17). 

To understand the role of the y-alumina support, two experiments were carried out (i) variation ofthe molar ratio ofIr/Re and (ii) the direct addition ofy-alumina to the system. Increasing the molar amount of the Re20y catalyst (molar ratio of 1 1.8) led to a better activity. An additional amount of y-alumina provided better productivity, but parallel studies on either Ir-2(H2) or supported Ir-17(C2H4) with the olefin metathesis catalyst Mo-1 in the presence of y-alumina were found to be detrimental to the reaction selectivity [143]. All of these results strongly support that the adsorption of iridium pincer catalysts on y-alumina could prevent the... 

In 2014, Guan and co-workers reported the direct synthesis of a-chiral tert-butanesulfinylamines from the reaction of racemic alcohols and Ellman s sulfinamide catalyzed by ruthenium (II) pincer catalyst 23 (Eq. 54) [176], providing an effective method for the synthesis of chiral amine derivatives. 

Zell T, Milstein D. Hydrogenation and dehydrogenation iron pincer catalysts capable of metal—ligand cooperation by aromatization/dearomatization. Acc Chem Res. 

Gartia et al. recently described a related coupling of furan with a small range of Grignard reagents using a nickel pincer catalyst 190 (Scheme 5.35). The first example is more properly a case of C(sp )—C(sp ) bond formation, and may be... 

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