Sol-gel matrix effects in organic chemistry   David Avnir Institute of Chemistry The Hebrew University of Jerusalem, Israel Key Laboratory of Organofluorine Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences April 19, 2019 

Molecularly doped sol-gel materials Background: Molecularly doped sol-gel materials

The preliminary motivation: To merge the small family of glasses and ceramics with the huge library of organic molecules and biomolecules: There are ~40 millions of these

The sol-gel porous glass formation by polycondenstation Si(OCH3)4 + H2O (SiOmHn)p + CH3OH Variations on this theme: the metals, semi-metals and their combinations the hydrolizable substituent the use of non-polymerizable substituents organic co-polymerizations (Ormosils) non-hydrolytic polymerizations Monomers of the type R-Si(OCH3)3 leading to(R-SiOmHn)p H+ or OH-

The Sol-Gel Process Sol Stage Gel Stage Xerogel Stage Thin Films Fibers Powders, patricles Hollow Spheres Membranes Porous Monoliths Dense Ceramic Aerogels

Sol-gel silica

Functionality within a sol-gel matrix * Molecules * Polymers * Proteins * Nanoparticles

Functionalization by entrapment of active components Porous Monomers, oligomers Sol Sol Gel Gel Xerogel monomer * Small molecules * Polymers * Proteins * Nanoparticles oligomer sol - - particle The concept is general and of very wide scope entrapped molecule

Organically doped sol-gel objects

Reactivity of the dopant through the nanopores An important and useful property: The entrapped functionalities are accessible to diffusing molecules from the outside, and to diffusing products from the inside, with minimal or no leaching. The reason:

From “Better Ceramics Through Chemistry” to “Better Chemistry Through Ceramics“ Matrix parameters which affect reactivity: The heterogenization by entrapment The confinement within cages and their rigidity 3. The porosity 4. The structure of the material 5. The chemical modification of the matrix 6. Co-entrapment of dopants

Matrix effects on reactivity 2. Opening example: Matrix effects on reactivity

Double-bond derivatized sol-gel silica Polymerization of monomers of the type R-Si(OCH3)3 Hydrobromination H. Frenkel

The hydrobromination reaction Bromine sponge The hydrobromination reaction We can see that the reaction kinetics can be followed in two ways: Following the visible absorption of bromine 2. Following the decrease in pH

Kinetics of the reaction through follow-up of Br2 consumption Vinylated silica

Kinetics of the reaction as detected by HBr release 2.2 2.25 2.3 2.35 2.4 X10 slower pH 10 20 30 40 50 Time (min) Kinetics of reactivity in nanopores depends on the analytical probe!

Bromine sponge: chain length effect n = 0, R = vinyl, (VTS): CH2=CH-Si n = 1, R = allyl, (ATS): CH2=CH-CH2-Si n = 2, R = butenyl, (BTS): CH2=CH-CH2-CH2-Si n = 6, R = octenyl, (OTS): CH2=CH-(CH2)6-Si The shorter chains are much more reactive than the longer ones - why? Time (s) 0.5 0.6 0.7 0.8 0.9 1 1.1 A/Ao VTS ATS BTS OTS Initial rates 2 4 6 8 10 12 Time (s)

% hydrobromination vinyl allyl butyl octyl Material Total Br/Si molar ratio 5 10 15 20 25 30 35 40 VTS ATS BTS OTS 50 60 70 80 90 100 % Hydrobromination Reactivity depends on the specific nano structure of the hybrid material

3. Matrix effect on catalysis

A. Porosity effects: Size-discrimination in catalytic disproportionation The catalyst: [RR’3N]+[RhCl4]-@silica R: (C8H17), R’: Me A. Rosenfeld, J. Blum

B. Cage effects: Synergistic catalyst for green chemistry Two components in a cage Hydrogenation of chlorinated environmental pollutants OH O OH = Chlorophenols 2,4,5-T PCBs DDT Cl-dioxins 6 h (44%) + (26%) H 2 O Cl The combined catalyst: Pd nanoparticles + [Rh(cod)Cl]2 OCH 2 CO H Cl 24 h (75 % ) Cl ClCH 2 CH Cl Cl 24 h (99%) hexane Cl 3 Cl 3 H H 24 h Cl C Cl hexane C (90%) CCl 3 C H 3 Cl Cl O O 24 h (93%) ClCH 2 CH2Cl O O Cl R. Abu-Reziq, J. Blum

Mechanism suggested by Bianchini, Psaro et al:

C. Matrix hydrophobization effects: All-hydrophobic catalytic reactions in water Three-phase catalysis: The EST process A novel three-phase microemulsion/solid heterogenization and transport method for catalysis R. Abu-Reziq, J. Blum

EST: Matrix induced selectivity Ethyl derivatized matrix Octyl derivatized matrix Catalyst: [CH3(C8H17)3N]+[RhCl4]- Surfactant: Cetyl(trimethylammonium)(p-toluenesulfonate) Conditions: 200 psi of H2 and heated at 80°C for 20 h

The sol-gel imprinting approach D. Imprinting effects: The sol-gel imprinting approach

Imprinting for catalysis Directing the seterochemistry of a reaction Forcing a cis-product in the Pd-acetate catalyzed Heck reaction   9:1 1:1 D. Tsvelikhovsky, J. Blum

4. Biocatalysis

Entrapped enzymes in sol-gel nanocages Protection against extreme pH Alkaline-phosphatase is active at pH 1! Blue: silica Green: with AOT Red: with CTAB H. Frenkel

Entrapped enzymes in sol-gel nanocages Protection against heat Acid phosphatase@alumina Increase in activity up to 60oC The activity at 750C, is higher than at room temperature by about two orders of magnitude. V. Vinogradov

Two protonated water molecules out of 100 is ~”pH=0”! The entrapped enzyme with few water molecules inside a pore, two of which are protonated: The nominal "pH" is very low Two protonated water molecules out of 100 is ~”pH=0”!

5. Opposing reactions in one reaction pot

The concept: Sol-gel isolation of mutually destructive chemical reagents F. Gelman, J. Blum

One-pot acid/base reactions Acid: Nafion Base: TBD Faina Gelamn, J. Blum

Oxidation/reductions in one pot RhCl[P(C6H5)3]3 91%

One-pot enzyme/catalyst pair 0.6 mmol acid, 2.5 mmol alcohol 0.01 mmol catalyst, 11U lipase F. Gelman, J. Blum

6. Getting a library of reactivities from a single molecule

Getting a library of acid-base equilibria from a single molecule Nanopore effects on the co-entrapment of an indicator-with a surfactant Anionic indicator AF Zwitterionic indicator ET(30) + Claudio Rottman

Affecting the immediate environment by co-entrapment of surfactants within the nanocages

ET(30), an acid or a base – your choice: The interpretation

Huge pKi shift for AF: 8 orders of magnitude

Surfactant-dye interactions

7. Matrix effect on photochemistry

Affecting the direction of photochromism Isomerization of spiropyrans D. Levy

Controlling the directionality of photochromism Colorless Colored Reversed photochromism in silica sol-gel matrices D. Levy et al, J. Phys. Chem., 92, 4734-4738 (1988).

…but normal photochromism in ethylated silica Colorless Colored D. Levy

Solar energy storage - solving the problem of back-reaction Light Py* - the donor Py Electron transfer Py* + MV.+ + Py+ MV2+ - the acceptor Energy storing pair 2MV.+ + 2H3O+ 2MV2+ + H2 + 2H2O Useful reaction The classical problem: MV.+ + Py+ MV2+ + Py back-reaction M. Ottolenghi

The nanoporosity approach: I. Separate spatially the donor and the acceptor by entrapment in a sol-gel matrix II. Allow them to communicate through the nanopores with a shuttler Py*@silica + TV2+ TV+ + Py+@silica MV2+@silica + TV+ TV+2 + MV.+ @silica Four hours, 5% yield of separated pair TV1+ Py MV2+ The redox potential of the MV pair is smaller than that of the TV pair TV+ + Py+@silica Py@silica + TV2+ A. Slama-Schwok, M. Ottolenghi

8. Conclusion Traditionally, variations in chemical reactivity have been affected by changing reagents and starting materials, that is by changing the molecules. Here we have seen that changing the heterogeneous environment of the molecules without changing them, opens a new way to control chemical reactivity: Catalysis, biochemistry, sensing, photochemistry

Abu-Reziq, R. , Armon, R. , Babonneau, F. , Banin, U. , Behar-Levy, H Abu-Reziq, R., Armon, R., Babonneau, F., Banin, U., Behar-Levy, H., Ben-David, O., Birenbaum, H., Blum, J., Braun, S., Ciriminna, R., Coradin, T., Elimelech, H., Fireman-Shoresh, S., Frenkel-Mullerad, H., Fuchs, I., Gelman, F., Ghattas, A., Grader, G.S., Hamza, K., Kaufman, V.R., Keinan, E., Khalfin, R., Kogan, A., Lev, O., Levy, A., Levy, D., Livage, J., Mandler, D., Marx, S., Mokari, T., Nairoukh, Z., Naor, H., Nedelec, J-M., Ottolenghi, M., Pagliaro, M., Polevaya, Y., Popov, I., Prior, Y., Rappoport, S., Reetz, M.T., Reisfeld, R., Rojanski, D., Rosenfeld, A., Rottman, C., Rouquerol, J., Samuel, J., Sarussi, L., Schubert, U., Schumann, H., Seri-Levy, A., Sertchook, H., Shabat, D., Shacham, R., Shtelzer, S., Shter, G.E., Shuster, M., Shvalb, A., Slama-Schwok, A., Tsvelikhovsky, D., Turiansky, A., Turyan, I., Vinogradov, V.V., Wellner, E., Zolkov, Ch., Zusman, R.