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Álvaro, Mercedes; Ferrer, Belén; Fornés, Vicente; Garcı́a, Hermenegildo

doi:10.1039/b108964c

Cited by 113 publications

(114 citation statements)

References 11 publications

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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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“…Here the key requirement is to enable optically generated excitation to propagate between particles with a suitably matching frequency response. Many of the proposed systems involve internal transfers of electronic excitation -for example, electron transfer activated by an applied electric field [54][55][56] or laser-induced RET [57][58][59][60][61]. Such devices hold significant promise for the furtherance of ultrafast communication and signal processing systems.…”

Section: Energy Transfer Between Dipole Arraysmentioning

confidence: 99%

Principles of Directed Electronic Energy Transfer

Andrews

Crisp

2007

Springer Series on Fluorescence

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“…[1][2][3][4] Carborane CB 11 H 12 2 results from the apical isomorphous substitution of a boron in dodecaborane with a carbon atom. 5 As result of this substitution and the extra carbon electron, a negative charge is introduced in the system and the carborane becomes an anionic species.…”

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confidence: 99%

“…3(A)). 12 Concerning the origin of the electron gained by MV 2+ to generate its radical cation, the most reasonable origin is CB 11 . However the fact that photoinduced electron transfer occurs with filtered light corresponding to the absorption of the charge transfer complex indicates that pre-association and charge transfer complex formation is a necessary prerequisite for photoinduced charge separation.…”

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confidence: 99%

Unexpected photochemistry and charge-transfer complexes of [CB₁₁H₁₂]⁻carborane

et al. 2008

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Although the [CB 11 H 12 ] 2 carborane does not exhibit an absorption band in UV, its triplet excited state can be generated upon 308 nm laser excitation; also unexpectedly carborane acts as electron donor forming a charge transfer complex with methylviologen that upon illumination gives rise to viologen radical cation.Since the initial report of Reed and co-workers describing the superacidity of carboranes in their protonic form, there is a renewed interest in this molecule. 1-4 Carborane CB 11 H 12 2 results from the apical isomorphous substitution of a boron in dodecaborane with a carbon atom. 5 As result of this substitution and the extra carbon electron, a negative charge is introduced in the system and the carborane becomes an anionic species. Carboranes are among the less nucleophilic species due to electron delocalization over the structure. [1][2][3][4] The chemistry and properties of carboranes have recently been reviewed. [5][6][7][8][9] Carborane does not exhibit any absorption band in the UV/Vis region and, therefore, no photochemistry is expected upon irradiation in this wavelength region. 5 Also, carborane cannot be oxidized in the potential range commonly available in conventional organic solvents, 5 although oxidation could occur at higher potentials. In sharp contrast with these two well-known properties of CB 11 H 12 2 carborane, herein we report the unexpected observation of photochemical activity of Cs [CB 11 H 12 ] and the formation of photoactive charge transfer complexes with a strong electron acceptor. Optical UV/Vis spectrum of Cs [CB 11 H 12 ] in acetonitrile solution shows no peaks in the 200-800 nm range and only an absorption tail growing to shorter wavelengths is observed (Fig. 1) (Fig. 2). The transient spectrum consists of a broad band expanding from 350 to 650 nm and peaking at 420 nm. The temporal profile of the signal was coincident in the complete spectral range, this being consistent with the photochemical generation of a single transient species (inset of Fig. 2). The signal decay fits well to a first-order kinetics with a half life of 16.2 ms. The signal from Cs [CB 11 H 12 ] generated upon the laser flash is quenched by oxygen (inset of Fig. 2). Taken together, these observations are consistent with the unexpected characterization of carborane triplet excited state. Since carboranes do not possess absorption bands in the UV, we performed an energy-dependence study to determine whether or COMMUNICATION www.rsc.org/chemcomm | ChemCommThis journal is ß

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Cited by 113 publications

References 11 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

Principles of Directed Electronic Energy Transfer

Unexpected photochemistry and charge-transfer complexes of [CB₁₁H₁₂]⁻carborane

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Untitled

Cited by 113 publications

References 11 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

Principles of Directed Electronic Energy Transfer

Unexpected photochemistry and charge-transfer complexes of [CB11H12]−carborane

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Unexpected photochemistry and charge-transfer complexes of [CB₁₁H₁₂]⁻carborane