Photoinduced Electron Transfer within Zeolite Cavities: cis-Stilbene Isomerization Photosensitized by 2,4,6-Triphenylpyrylium Cation Imprisoned inside Zeolite Y

Corma, Avelino; Fornés, Vicente; García, H.; Miranda, Miguel A.; Primo, Jaime; Sabater, Marı́a J.

doi:10.1021/ja00085a006

Cited by 101 publications

(112 citation statements)

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“…[10][11][12][13][14][15][16][17] The organometallic guests in zeolite hosts become polarized by electrostatic fields resulting from the interplay between positively charged extra-framework cations and negatively charged zeolite walls and are expected to show substantially enhanced reactivity compared to the parent compounds. 18 Therefore, as demonstrated in the past, 18 zeolitic voids would function as "nanoscale reaction chambers", where the reactivity of guest organometallic complexes can provide molecular insights into the elementary steps of heterogeneous catalysis.…”

Section: Introductionmentioning

confidence: 99%

Structure and Enhanced Reactivity of Chromocene Carbonyl Confined inside Cavities of NaY Zeolite

et al. 2009

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Chromocene (Cp 2 Cr) hosted inside the supercage cavities of a NaY zeolite undergoes a structural distortion induced by the strong local electric fields generated by charge-balancing counterions. This effect, clearly observed by an in situ Cr K-edge extended X-ray absorption fine structure (EXAFS) study, is the key factor in enhancing the reactivity of Cp 2 Cr toward CO. The Cp 2 Cr(CO) adducts initially formed are not as stable as when hosted in nonpolar environments such as toluene solution or polystyrene. The presence of strong anionic/ cationic pairs (Y -/Na + ) favors, in a CO atmosphere, the loss of a Cp ring driven by an electron transfer mechanism (accompanied by ligand rearrangement) that results in the formation of the charged [CpCr(CO) 3 ] - and [Cp 2 Cr(CO)]+ carbonyl species that are stabilized by Na + and Y -pairs. Shape selectivity of the supercage cavity of the Y zeolite is necessary for this reaction, as it can host the two Cp 2 Cr molecules needed for disproportionation. Fast Fourier transform infrared (FTIR) spectroscopy, working in operando conditions, allows us to follow the time evolution of the IR stretching modes peculiar of reactants and products and thus to infer a reaction mechanism. The combination of quantum mechanical calculation with an in situ EXAFS study supports the hypothesis made on the basis of IR results. The work is further demonstration that zeolitic voids act as "nanoscale reaction chambers", where the reactivity of guest organometallic complexes can provide molecular insights into the elementary steps of heterogeneous catalysis. In this context, the investigation of metallocene reactivity inside a polar matrix can be extremely useful to understanding their properties in polymerization conditions, where they are usually found as part of an ion pair, together with the anionic form of the activator (e.g., MAO).

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Section: Introductionmentioning

confidence: 99%

Structure and Enhanced Reactivity of Chromocene Carbonyl Confined inside Cavities of NaY Zeolite

et al. 2009

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“…2 After the encapsulation, TP + remains mechanically immobilized inside the zeolite Y supercages, but it still can interact with smaller molecules through the cavity windows.…”

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confidence: 99%

Electrocatalysis of neurotransmitter catecholamines by 2,4,6-triphenylpyrylium ion immobilized inside zeolite Y supercages

Doménech¹,

Doménech‐Carbó²,

Garcı́a³

et al. 1999

Chem. Commun.

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2,4,6-Triphenylpyrylium ions entrapped inside the supercages of Y zeolite exert a remarkable catalytic effect toward the electrochemical oxidation of dopamine and norepinephrine (neurotrasmitter catecholamines) in neutral aqueous media.Encapsulation of organic species inside the rigid matrix of microporous zeolites has proved to be a general methodology to control the molecular properties of the incorporated guest. 1 Zeolites are a large family of crystalline aluminosilicates whose structure defines strictly uniform channels and cavities of molecular dimensions (micropores). It is in these internal voids where a guest can be accommodated provided that its molecular size is smaller than the void dimensions. In particular, the structure of zeolite Y is formed by an array of spherical cavities (1.4 nm diameter) that are tetrahedrally interconnected through four smaller apertures (0.74 nm diameter).We have already reported that the bulky 2,4,6-triphenylpyrylium ion (TP + , ≈ 1.3 nm) can be prepared inside the zeolite Y supercages through a 'ship-in-a-bottle' synthesis that relies on the diffusion of much smaller synthetic precursors. 2 After the encapsulation, TP + remains mechanically immobilized inside the zeolite Y supercages, but it still can interact with smaller molecules through the cavity windows.Recently one of us has shown that while the BF 4 2 salt of TP + in water undergoes a rapid hydrolytic ring opening, when TP + is encapsulated within the restricted space provided by the supercages of zeolite, the host framework protects it from the nucleophilic attack of water. 3 As a result, TP + within Y zeolite (TPY) is completely persistent in water. This opens the opportunity for new applications of TP + in aqueous media, as reported herein on the catalytic effect of TPY on the electrochemical oxidation of catecholamines in aqueous solution.The electrochemistry of pyrylium ions in solution is well understood. TP + undergoes one-electron reduction in protic solvents. 4 Controlled potential electrolysis produces the corresponding dipyran which in turn can be reoxidized back to TP + . In aprotic solvents, reduction of pyrylium ions leads to the corresponding bipyranylidene together with pyrane. 5 In this case, the transient reduction wave is controlled kinetically by the irreversible dimerization of the radicals formed after the initial electron transfer. 6 Bipyranylidene and pyrane are produced by the reversible reduction of the dimer. 7 We have found that upon encapsulation in the internal voids of zeolites, owing to the impossibility to form dimers, pyrylium ions display an apparently more simple electrochemistry consisting on the quasi-reversible reduction to TP. Compartmentalization of TP + inside the zeolite Y impedes its diffusion and eventually that of the corresponding TP pyranyl radicals, and therefore radical coupling is inhibited.Preliminary experiments on the electrochemistry of TP + incorporated within zeolite Y confirmed the inhibition of dimerization processes. Paraloid B72 † and Elvacite 2044, ‡ w...

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“…[6] To prepare BTP@Y, a solution of dichalcone [1,4-bis(3-phenyl-3-oxo-1-propene)phenylene] (50 mg) and acetophenone (50 mg) in isooctane (25 mL) was stirred magnetically in the presence of thermally dehydrated (500 8C) HY zeolite (PQ CBV 720, 1 g) at reflux temperature for seven days. Dichalcone was in turn obtained by Claisen ± Schmidt condensation of two equivalents of acetophenone (9.84 g) with one equivalent of terephthaldehyde (Aldrich, 5 g) in ethanol (25 mL) containing NaOH (3.28 g) at room temperature.…”

Section: Methodsmentioning

confidence: 99%

“…Following these previous studies, herein we report the synthesis, characterisation, electrochemical properties and photocatalytic activity of 1,4-bis(3,5-diphenyl-4-pyrylium)phenylene, commonly known as bipyrylium (BTP ), encapsulated inside the cavities of zeolite Y. By considering the reported molecular modelling for TP inside zeolite Y [6] and the fact that BTP is an even larger molecule, it is obvious that BTP can not be accommodated inside a single zeolite Y supercage (13 ä diameter) and would require two neighbour supercages. Therefore the synthesis of BTP adsorbed in the pore of zeolite Y is particularly challenging.…”

Section: Introductionmentioning

confidence: 94%

Ship‐in‐a‐Bottle Synthesis of a Large Guest Occupying Two Y Zeolite Neighbour Supercages: Characterisation and Photocatalytic Activity of the Encapsulated Bipyrylium Ion

et al. 2003

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Photoinduced Electron Transfer within Zeolite Cavities: cis-Stilbene Isomerization Photosensitized by 2,4,6-Triphenylpyrylium Cation Imprisoned inside Zeolite Y

Cited by 101 publications

References 0 publications

Structure and Enhanced Reactivity of Chromocene Carbonyl Confined inside Cavities of NaY Zeolite

Structure and Enhanced Reactivity of Chromocene Carbonyl Confined inside Cavities of NaY Zeolite

Electrocatalysis of neurotransmitter catecholamines by 2,4,6-triphenylpyrylium ion immobilized inside zeolite Y supercages

Ship‐in‐a‐Bottle Synthesis of a Large Guest Occupying Two Y Zeolite Neighbour Supercages: Characterisation and Photocatalytic Activity of the Encapsulated Bipyrylium Ion

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