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Volumn 131, Issue 1, 2009, Pages 357-367

Photoswitchable catalysts: Correlating structure and conformational dynamics with reactivity by a combined Experimental and computational approach

Author keywords

[No Author keywords available]

Indexed keywords

ACTIVE SITE; AZOBENZENE GROUP; COMPUTATIONAL APPROACH; COMPUTATIONAL INVESTIGATION; CONFORMATIONAL DYNAMICS; E-ISOMERS; GENERAL BASE CATALYSIS; HENRY REACTIONS; NITROALDOL; NMR SPECTROSCOPY; PHOTO MODULATION; PHOTO-SWITCHABLE; PHOTOCONTROL; PROTON AFFINITY; RESIDUAL DIPOLAR COUPLINGS; SOLID-STATE STRUCTURES; SYNTHETIC ROUTES; X-RAY CRYSTAL STRUCTURE ANALYSIS;

EID: 67849109510     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja807694s     Document Type: Article
Times cited : (128)

References (71)
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    • The only exception relates to a photoswitchable Lewis acid; however, no catalysis was reported. Lemieux, V.; Spantulescu, M. D.; Baldridge, K. K.; Branda, N. R. Angew. Chem., Int. Ed. 2008, 47, 5034-5037.
    • The only exception relates to a photoswitchable Lewis acid; however, no catalysis was reported. Lemieux, V.; Spantulescu, M. D.; Baldridge, K. K.; Branda, N. R. Angew. Chem., Int. Ed. 2008, 47, 5034-5037.
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    • See Supporting Information.
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    • A similar energy difference has been obtained between equatorial and axial W-methyl piperidine, 3.9 kcal/mol at the MP2/cc-pVTZ level: Dos Santos, F. P.; Tormena, C. F J. Mol. Struct. (THEOCHEM) 2006, 763, 145-148.
    • A similar energy difference has been obtained between equatorial and axial W-methyl piperidine, 3.9 kcal/mol at the MP2/cc-pVTZ level: Dos Santos, F. P.; Tormena, C. F J. Mol. Struct. (THEOCHEM) 2006, 763, 145-148.
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    • The two conformers could initially not be distinguished because of a fitting problem as 1DC-N becomes very small (because of the small gyromagnetic ratios) and the PALES program (Zweckstetter, M, Bax, A. J. Am. Chem. Soc. 2000, 122, 3791-3792) used for fitting the data does not allow for weighing of couplings within the fitting procedure, resulting in equally good fits for E-1b and i-1b, To obtain conclusive results, the corresponding coupling was scaled by a factor of 1000, while the bond length was reduced in the coordinate file to 10% of its original value using the program MolArch, Immel, S. MolArch, Molecular architecture modelling program; Universitat Leipzig: Leipzig, 2008, As 1D is proportional to 1/r3 the physical information of 1DC-N is unchanged by this procedure
    • C-N is unchanged by this procedure.
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    • This method is described in: Thiele, C. M. J. Org. Chem. 2004, 69, 7403-7413
    • This method is described in: Thiele, C. M. J. Org. Chem. 2004, 69, 7403-7413.
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    • There are many more possible twist or twist-boat intermediates and transition states, depending on which C-CorC-N bond in the ring is rotated relative to its opposite counterpart and in what direction. We have refrained from locating all of them, but from the present results it is already clear that the overall barrier must be in the interval between ∼7-13 kcal/mol, implying notable activation for this process
    • There are many more possible twist or twist-boat intermediates and transition states, depending on which C-CorC-N bond in the ring is rotated relative to its opposite counterpart and in what direction. We have refrained from locating all of them, but from the present results it is already clear that the overall barrier must be in the interval between ∼7-13 kcal/mol, implying notable activation for this process.
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    • For example: AE = 11.4 kcal/mol at B3LYP/6-31G* for the C2-symmetric twist-chair transition state (or half-chair), cf. structure 10 in the following reference, where a value of 11.9 kcal/mol has been obtained at MP2/6-31G* Leong, M. K.; Mastrryukov, V. S.; Boggs, J. E. J. Phys. Chem. 1994, 98, 6961-6966.
    • For example: AE = 11.4 kcal/mol at B3LYP/6-31G* for the C2-symmetric twist-chair transition state (or half-chair), cf. structure 10 in the following reference, where a value of 11.9 kcal/mol has been obtained at MP2/6-31G* Leong, M. K.; Mastrryukov, V. S.; Boggs, J. E. J. Phys. Chem. 1994, 98, 6961-6966.
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    • Another indication is given by the fact that we did not observe differentiation of enantiotopic faces, which is to be expected in a chiral orienting medium if no rotation of the steric blocker (converting one enantiotopic face into the other) is occurring
    • Another indication is given by the fact that we did not observe differentiation of enantiotopic faces, which is to be expected in a chiral orienting medium if no rotation of the steric blocker (converting one enantiotopic face into the other) is occurring.
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    • If the transition-state structure of this rotation, 1-TSrot, is used, the quality of the fit is further reduced (q = 0.426, Figure 3a, black triangles).
    • If the transition-state structure of this rotation, 1-TSrot, is used, the quality of the fit is further reduced (q = 0.426, Figure 3a, black triangles).
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    • -1 for δS‡. Rate constants and half lives, which can be calculated from δH‡ and δS‡ by the thermodynamic formulation of the Eyring equation, are extremely sensitive to these quantities.
    • -1 for δS‡. Rate constants and half lives, which can be calculated from δH‡ and δS‡ by the thermodynamic formulation of the Eyring equation, are extremely sensitive to these quantities.
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    • That this transition state indeed connects Z-1a and E-1a was verified by reoptimization at B3LYP/3-21G and following the intrinsic reaction coordinate (see: (a) Gonzalez, C.; Schlegel, H. B. J. Chem. Phys. 1989, 90, 2154-2161.
    • That this transition state indeed connects Z-1a and E-1a was verified by reoptimization at B3LYP/3-21G and following the intrinsic reaction coordinate (see: (a) Gonzalez, C.; Schlegel, H. B. J. Chem. Phys. 1989, 90, 2154-2161.
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    • The corresponding DFT values for AH* (not included in Table 1) are 23.0, 22.9, and 23.6 kcal/mol for 1a, 1b, and 1c, respectively.
    • The corresponding DFT values for AH* (not included in Table 1) are 23.0, 22.9, and 23.6 kcal/mol for 1a, 1b, and 1c, respectively.
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    • a of the base to be measured.
    • a of the base to be measured.
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    • Note that the higher concentration used in preparative irradiation experiments increased the absorbance of the solution such that usually even after prolonged irradiation times the photostationary-state mixtures contained a larger amount of E isomer as compared to irradiating analytical samples of much lower concentration. For these reasons, the conditions necessary to accurately determine the kinetics, i.e. the rather high catalyst concentrations employed in the NMR experiments, precluded switching of the catalysts in situ. However, this does only constitute a drawback in bulk or solution-phase catalysis associated with high optical densities-a drawback that photochemistry suffers from in general-yet an application utilizing mono-or multilayers of immobilized catalysts should be feasible
    • Note that the higher concentration used in preparative irradiation experiments increased the absorbance of the solution such that usually even after prolonged irradiation times the photostationary-state mixtures contained a larger amount of E isomer as compared to irradiating analytical samples of much lower concentration. For these reasons, the conditions necessary to accurately determine the kinetics, i.e. the rather high catalyst concentrations employed in the NMR experiments, precluded switching of the catalysts in situ. However, this does only constitute a drawback in bulk or solution-phase catalysis associated with high optical densities-a drawback that photochemistry suffers from in general-yet an application utilizing mono-or multilayers of immobilized catalysts should be feasible.
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    • For a discussion of the conformational behavior of piperidines, see:, Wiley: New York, and references therein
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    • Eliel, E.L.1    Wilen, S.H.2
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    • The reactivity of the Z isomer Z-1b was also lowered, most likely because the steric demand of the tert-butyl group hinders the nitroalkane to approach the basic catalyst site.
    • The reactivity of the Z isomer Z-1b was also lowered, most likely because the steric demand of the tert-butyl group hinders the nitroalkane to approach the basic catalyst site.
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    • At the B3LYP/cc-pVTZ/PCM(acetonitrile) level, the relative energies of i-1a,i-1b, and i-1c are 3.9, 7.1, and 5.8 kcal/mol, respectively, i.e. quite similar to the gas-phase δE values in Table 4
    • At the B3LYP/cc-pVTZ/PCM(acetonitrile) level, the relative energies of i-1a,i-1b, and i-1c are 3.9, 7.1, and 5.8 kcal/mol, respectively, i.e. quite similar to the gas-phase δE values in Table 4.
  • 67
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    • +. This particular result should be taken with care in light of the performance of the continuum model for predicting the basicities of Z vs E isomers (vide supra). However, the qualitative finding that the N-inverted isomers i-1 are more basic than their more stable chair conformers E-1 forms should be reliable.
    • +. This particular result should be taken with care in light of the performance of the continuum model for predicting the basicities of Z vs E isomers (vide supra). However, the qualitative finding that the N-inverted isomers i-1 are more basic than their more stable chair conformers E-1 forms should be reliable.
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    • In a recent B3LYP study of the Henry reaction catalyzed by a cinchona alkaloid, a barrier of 10.8 kcal/mol for deprotonation of nitromethane has been computed in a THF continuum: Hammar, P, Marcelli, T, Hiemstra, H, Himo, F. Adv. Synth. Catal. 2007, 349, 2537-2548
    • In a recent B3LYP study of the Henry reaction catalyzed by a cinchona alkaloid, a barrier of 10.8 kcal/mol for deprotonation of nitromethane has been computed in a THF continuum: Hammar, P.; Marcelli, T.; Hiemstra, H.; Himo, F. Adv. Synth. Catal. 2007, 349, 2537-2548.
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    • For comprehensive reviews on the effect of conformational changes on reactivity in organic chemistry, see: (a) Seeman, J. I. Chem. Rev. 1983, 83, 83-134
    • For comprehensive reviews on the effect of conformational changes on reactivity in organic chemistry, see: (a) Seeman, J. I. Chem. Rev. 1983, 83, 83-134.
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    • Reference 33, pp 647 -655
    • (b) Reference 33, pp 647 -655.


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.