Scandium(III)‐Zeolites as New Heterogeneous Catalysts for Imino‐Diels–Alder Reactions

Olmos, Andrea; Louis, Benoît; Pale, Patrick

doi:10.1002/chem.201103624

Cited by 20 publications

(7 citation statements)

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“…Systems such as the TM coordination complexes, 47−55 TM-exchanged clays, 52 and TM-exchanged zeolites 51 have been used earlier to catalyze DAC reactions. Among others, 50,54,56 catalytic systems based on Cu(I), 54,56 Cu(II), 56,57 Ni(II), 47,56 Zn(II), 47,56 Sc(III), 47,51,55 and Cr(III) 52,53,56 have been investigated. Typically, the reaction starts with a η 2 /η 4 -type coordination of the dienophile/diene to the metal ion.…”

Section: Introductionmentioning

confidence: 99%

“…TM-based catalysts are widely employed in DAC chemistry. Systems such as the TM coordination complexes, − TM-exchanged clays, and TM-exchanged zeolites have been used earlier to catalyze DAC reactions. Among others, ,, catalytic systems based on Cu(I), , Cu(II), , Ni(II), , Zn(II), , Sc(III), ,, and Cr(III) ,, have been investigated.…”

Section: Introductionmentioning

confidence: 99%

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Mechanistic Insight into the [4 + 2] Diels–Alder Cycloaddition over First Row d-Block Cation-Exchanged Faujasites

et al. 2018

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The Diels–Alder cycloaddition (DAC) is a powerful tool to construct C–C bonds. The DAC reaction can be accelerated in several ways, one of which is reactant confinement as observed in supramolecular complexes and Diels–Alderases. Another method is altering the frontier molecular orbitals (FMOs) of the reactants by using homogeneous transition-metal complexes whose active sites exhibit d-orbitals suitable for net-bonding orbital interactions with the substrates. Both features can be combined in first row d-block (TM) exchanged faujasite catalysts where the zeolite framework acts as a stabilizing ligand for the active site while confining the reactants. Herein, we report on a mechanistic and periodic DFT study on TM-(Cu(I), Cu(II), Zn(II), Ni(II), Cr(III), Sc(III), V(V))exchanged faujasites to elucidate the effect of d-shell filling on the DAC reaction between 2,5-dimethylfuran and ethylene. Two pathways were found: one being the concerted one-step and the other being the stepwise two-step pathway. A decrease in d-shell filling results in a concomitant increase in reactant activation as evidenced by increasingly narrow energy gaps and lower activation barriers. For models holding relatively small d-block cations, the zeolite framework was found to bias the DAC reaction toward an asynchronous one-step pathway instead of the two-step pathway. This work is an example of how the active site properties and the surrounding chemical environment influence the reaction mechanism of chemical transformations.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Mechanistic Insight into the [4 + 2] Diels–Alder Cycloaddition over First Row d-Block Cation-Exchanged Faujasites

et al. 2018

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“…Y and Sc are far more Lewis acidic than transition metals and thus might be expected to be faster catalysts if they proceed via a similar mechanism. The catalytic activity of heterogeneous, single-site Y and Sc cations on silica for dehydrogenation/hydrogenation catalysis has not been explored, but the Lewis acidity of these cations, particularly as triflate salts Sc(CF 3 SO 3 ) 3 and Y(CF 3 SO 3 ) 3 , has been exploited by a number of researchers to catalyze a number of reactions including catalytic acylation, Diels–Alder condensation, reductive amination, ring-opening polymerization, and others. , Olmos and co-workers have investigated similar chemistry over Sc-exchanged zeolites. − The very high Lewis acidity of organometallic scandium and yttrium complexes such as Cp* 2 ScMe (Cp* = η 5 -C 5 (CH 3 ) 5 ) has been implicated in the ability of such complexes to activate C–H bonds in alkanes, including methane. , However, mechanistic examination of Y and Sc catalysts ligated by cyclopentadienyl type ligands suggests that these complexes activate C–H bonds via a σ bond metathesis mechanism rather than via heterolytic cleavage. , Since the cyclopentadienyl type ligands typically employed to support organometallic Y and Sc complexes are expected to provide a local electronic environment around the metal centers substantially different from that provided by the siloxides of “bare” SiO 2 , it is unclear whether the mechanistic insights obtained from previous organometallic studies will carry over to organometallic Y or Sc cations grafted directly to silica supports. Examining the reactivity of such structures may provide more general insight into the role of the local electronic environment in dictating reaction mechanisms for C–H bond activation under steady-state reaction conditions or during precatalyst activation.…”

Section: Introductionmentioning

confidence: 99%

Silica-Supported, Single-Site Sc and Y Alkyls for Catalytic Hydrogenation of Propylene

Getsoian

Miller

et al. 2017

Organometallics

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Single-site Sc and Y on silica catalysts have been prepared by aqueous and organometallic grafting methods. The former yields Y(III) ions with five bonds at an average bond distance of 2.31 Å by X-ray absorption spectroscopy. Although the aqueous synthesis gave single-site Y with low coordination number, these were not catalytic for alkane dehydrogenation or olefin hydrogenation. Single-site Sc(III) and Y(III) species were also prepared by grafting Sc(CH2Si(CH3)3)3(THF)2 and Y(CH2Si(CH3)3)3(THF)2, respectively, and these are catalysts for olefin hydrogenation at temperatures from about 60 to 100 °C; however, they were thermally unstable at higher temperatures necessary for alkane dehydrogenation. The structure of the grafted Y complex was determined by X-ray absorption spectroscopy, IR, and NMR. Grafting led to protonolysis of two of the three CH2Si(CH3)3 ligands. Additionally, there was loss of one THF ligand. The EXAFS indicated that there were four Y–ligand bonds in the surface species, two at 2.16 Å and two at 2.39 Å. The metal–alkyl ligand was thought to be necessary for catalytic activity and likely proceeds through a σ bond metathesis mechanism. In the single-site centers without alkyl bonds, Sc and Y ions cannot generate metal–alkyl or metal–hydride moieties in situ. We conclude that this is likely due to the very high M–O–Si bond strengths, which must be broken through heterolytic dissociation of C–H bonds during alkane activation for either alkane dehydrogenation or olefin hydrogenation reactions. This study demonstrates the importance of precatalyst choice versus in situ formation of reactive intermediates to produce active catalysts for alkane bond activation.

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“…Thus, the stereodifference is inadequate for the induction caused by the amino acid stereocenter. Excitingly, an outside Houk‐type model can justify the stereochemical result; interface of the ester group either with the zeolite or scandium (both) possibly favors the outside arrangement, while the spherical shape of the zeolite used (USY) preferes a more or less spherical instead of extended transition‐state, resulting in the anti diastereoisomer (Scheme ) …”

Section: Asymmetric Reaction Of Dainshefsky Dienes With Imines Derivementioning

confidence: 99%

Applications of Dainshefsky's Dienes in the Asymmetric synthesis of Aza‐Diels‐Alder Reaction

Koshvandi

Heravi

2018

The Chemical Record

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Asymmetric hetero-Diels-Alder (AHDA) reactions provide a multitude of opportunities for the highly efficient, regio- and stereoselective construction of various heterocycles in enantiomerically pure form. The asymmetric aza-Diels-Alder (A-aza-DA) reaction using diversely hetero-dienophiles and hetero-dienes have been increasingly developed as a valuable method for the synthesis of functionalized nitrogen ring systems. The purpose of this review is to give a detailed discussion of the A-aza-DA reaction particularly, the stereoselective reactions of imines as dienophiles with Dainshefsky dienes to obtain optically pure aza-Diels-Alder products. The development of stereoselective variants of the reaction make use of imines as the dienophile and Dainshefsky dienes is at the forefront of these studies. This review updates the A-aza-DA reactions covering the literature from 1972 till date.

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Scandium(III)‐Zeolites as New Heterogeneous Catalysts for Imino‐Diels–Alder Reactions

Cited by 20 publications

References 92 publications

Mechanistic Insight into the [4 + 2] Diels–Alder Cycloaddition over First Row d-Block Cation-Exchanged Faujasites

Mechanistic Insight into the [4 + 2] Diels–Alder Cycloaddition over First Row d-Block Cation-Exchanged Faujasites

Silica-Supported, Single-Site Sc and Y Alkyls for Catalytic Hydrogenation of Propylene

Applications of Dainshefsky's Dienes in the Asymmetric synthesis of Aza‐Diels‐Alder Reaction

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