Volume 1 of JACS: 1879

Volume 1 of Chem. Mater.: 1989

The new motto (80’s) has been:

“Better Ceramics Through Chemistry”

Publications in the sol-gel materials field

1980 1985 1990 1995 2000 2005 20100

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1000

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3500

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Papers Patents (cumulative)

25 YEARS OF SOL-GEL RESEARCH: CONTRIBUTIONS TO CHEMISTRY

 David Avnir

 Institute of Chemistry

The Hebrew University of Jerusalem

75th Meeting of the Israel Chemical SocietyTel-Aviv, 25-16.1.2010

“Better Ceramics Through Chemistry”

The motto of this lecture:# What has chemistry gained from sol-gel research

# How do solid matrices affect a chemical reaction?

# What can be done in heterogeneous chemistry that homogeneous reactions cannot achieve?

My main partners over the years

Jochanan BlumSergei BraunOvadia LevDaniel MandlerSharon MarxMichael OttolenghiRenata Reisfeld

1. The Heterogeneous environment:

Silica

Silica

Synthesis of silica by the sol-gel polycondensation

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

H+ or OH-

Controlled nanoporosity and cage geometry

Surface area and pore volume of silica as a function of pH and water/silane ratio

Y. Polevaya, M. Ottolenghi, D. Avnir, J. Sol-Gel Sci. Tech., 5, 65-70, (1995)

Sol Gel XerogelSol Gel Xerogel

sol-particleEntrapped species

monomeroligomer

-

Organic heterogenizationPhysical entrapment of molecules within sol-gel matrices

* Small molecules

* Polymers

* Proteins

* Nanoparticles

Monomers,oligomers

The concept is general and of very wide scope

Important property:Reactivity is possible with the entrapped species

Physical entrapment vs covalent entrapment

Matrix parameters which can affect chemical reactivity:

# The fixation by entrapment within the matrix

# The confined environment of cages and narrow pores

# The porosity

# The chemical modification of the matrix

# The co-entrapment of a surfactant

2. Affecting reactivity by the entrapment

* Hydrophobic catalysts in water

* The back-reaction problem in energy storage

* One-pot reactions with mutually destructive reagents

Using hydrophobic catalysts in water

With F. Gelman. J. Blum, D. Avnir J. Molec. Catal., A: Chem., 146, 123 (1999)

ee = 78% (BPPM)

The advantages of sol-gel entrapment# Reactivity in incompatible solvents# Covalent bonding chemistry is not needed# Recyclability and separation

Electron transfer

Py

Light Py* - the donor

Py* +

MV2+ - the acceptor

MV.+ + Py+

2MV.+ + 2H3O+ 2MV2+ + H2 + 2H2O

The classical problem:

MV.+ + Py+ MV2+ + Py

The problem of back-reaction in energy storage

Energy storing pair

Useful reaction

back-reaction

Py*@silica + TV2+

N N

2Br

Four hours, 5% yield of separated pair

The solution: I. Separate spatially the donor and the acceptor in a matrix

II. Allow them to communicate with a shuttler

A. Slama-Schwok, M. Ottolenghi and D. Avnir, Nature, 355, 240 (1992)

TV+ + Py+@silica

MV2+@silica + TV+ TV+2 + MV.+@silica

TV+ + Py+@silica Py@silica + TV2+

TV2+ Py MV2+

One-pot reactivity from opposing reagents

The concept:

Entrapped reagents are not accessible to each other, but are accessible to diffusing substrates

A

B + C

D

acid

baseOne pot, one step

Acid, Base, C

The acid and base are entrapped, separately

A D

32%

One-pot acid/base reactions

Base: TBDAcid: Nafion

Faina Gelamn, J. Blum, D. Avnir, Angew. Chem. Int. Ed., 40, 3647 (2001)

F. Gelman, H. Schumann, J. Blum, D. Avnir J. Sol-Gel Sci. Tech., 26, 43 (2003); J. Am. Chem. Soc., 122, 11999 (2000)

Opposing catalyst and acids

RhCl[P(Ph)3]3@silica

F. Gelamn, J. Blum, D. Avnir, New J. Chem., 27, 205 (2003)

Simultaneous oxidation-reduction reactivity

One-pot lipase / catalyst pairOne-pot lipase / catalyst pair

+ CH3(CH2)nCH2OH

Catal@S-G Lipase@S-GH2

CH2 CH(CH2)8COOH

CH3(CH2)9COOCH2(CH2)nCH3

Catalysts: Rh2Co2(CO)12

Rh(PPh3)3Cl

Biocatalysis and organometallic catalysis in one pot

F. Gelman, J. Blum, D. Avnir J. Am. Chem. Soc., 124, 14460 (2002)

All possible combinations:

3. Cage-confinement effects on reactivity# Radical photo-rearrangement

# Synergism in catalysis

# Unusual enzyme reactivity

The photo-Fries rearrangement

CH3

H3C CH3

OO

H3C CH3

CH3

H3C CH3

O

OH

CH3

CH3

h

Pentane

D. Avnir, P. de Mayo, J. Chem. Soc. Chem. Comm., 1109 (1978)

Radical cage effect of silica

Only 5% in pentane, but 37% in silica (at 40%, conversion)

Cl 3

OCH 2 CO 2H

Cl

Cl 3

Cl24 h (75 % )

Cl

(99%)

C

CCl3

Two components in a cage: Catalytic synergism

Hydrogenation of chlorinated environmental pollutants

Cl CClH

C H 3

(90%)

OH

H

Cl

6 h

H 2 O

ClCH 2CH 2Cl

(44%) + (26%)

=OH

O

O

O

hexane

O

O

hexane24 h

24 hClCH 2 CH2Cl

Cl

ClCl

(93%)

24 h

A. Ghatas, R. Abu-Reziq, J. Blum, D. Avnir Green Chem., 5, 40 (2003)

The combined catalyst:Pd nanoparticles + [Rh(cod)Cl]2

Chlorophenols

2,4,5-T

PCBs

DDT

Cl-dioxins

C. Bianchini, R. Psaro et al, J. Am. Chem. Soc., 128, 7065 (2006)

“Pd(0) is able to reduce benzene to cyclohexane with a mechanism that involves disproportionation of the cyclohexa-1,3-diene product and fast cyclohexene hydrogenation; Rh(I) is faster than Pd(0) in reducing cyclohexa-1,3-diene, yet slower in the conversion of cyclohexene to cyclohexane”

Mechanism suggested by Bianchini, Psaro et al:

C. Bianchini, R. Psaro et al, J. Am. Chem. Soc., 128, 7065 (2006)

The confinement of the two catalysts within a cage

Un-orthodox reactivity and unusual stability of sol-gel entrapped enzymes

Alkaline-phosphatase is active at pH 1!

H. Frenkel-Mullerad, D. Avnir J. Am. Chem. Soc. 127, 8077 (2005)

Blue: silicaGreen: with AOTRed: with CTAB

0

10

20

30

40

50

60

70

0.9 2.2 3.0 3.5 11.0 12.0 13.0

T.O

.N. (

1/s)

pH

AEntrapped

0

10

20

30

40

50

60

70

0.9 2.2 3.0 3.5 11.0 12.0 13.0

AOT CTAB N.S.

T.O

.N. (

1/s)

pH

BSolution

Enzymatic activity under very extreme conditions

A basic enzyme is active at pH 1!

Why is the narrow cage so efficient in protecting the enzyme?

“The collapse of thermodynamics”

Two protonated water molecules out of 100 is ~ ”pH=0”!

Acid phosphatase is active under extreme alkaline conditions

Right: silica; left: silica/CTAB

In solution: Zero activity above pH 10

4. Porosity effects on reactivity

# The inherent porosity of silica

# Imprinted porosity

Size-discrimination in disproportionation reactivity

A. Rosenfeld, J. Blum, D. AvnirJ. Catal. 164, 363 (1996)

The catalyst:[RR’3N]+[RhCl4]-@silicaR: (C8H17), R’: Me

[RR’3N]+[RhCl4]-@silica

SG-1: R: (C8H17), R’: Me

SG-2: RR’3N: [Me3N(CH2)3Si(OMe)3]

SG-1 (—) and SG-2 (– – –)

Pore-accessibility effects on the disproportionation reactivity of 1,2-dihydronaphthalene

naphthalene and tetralin

dihydronaphthalene

Si(OEt)4 and RSi(OEt)3

Directing reactivity through imprinting of the matrixForcing a cis-product in the Pd-acetate catalyzed Heck reaction

 

D. Tsvelikhovsky, D. Pessing, D. Avnir, J. Blum, Adv. Synth. & Catal., 350, 2856 (2008)

9:1

1:1

5. Affecting reactivity by covalent modifying the material

Co-polycondensation of Si(OEt)4 and RSi(OEt)3

# All-hydrophobic catalytic reactions in water

The emulsion contains the substrate

The emulsion spills its content into the porous catalyst material

All-hydrophobic catalytic reactions in water

Hydrophobic chains

The catalyst is entrapped in a partially hydrophobic silica sol-gel matrix

R. Abu-Reziq, J. Blum, D. Avnir Angew. Chem. Int. Ed., 41, 4132 (2002)

The catalytic process takes place A micelle is reassembled and

leaves with products inside

Three-phase catalysis:The EST processA novel three-phase microemulsion/solid heterogenization and transport method for catalysis

All-hydrophobic catalytic reactions in water

R. Abu-Reziq, J. Blum, D. Avnir Angew. Chem. Int. Ed., 41, 4132 (2002)

(1)

O O

84%

O OOH

+

52% 36%

(2)

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

Ethyl derivatized matrix

EST: Matrix induced selectivity

6. Affecting reactivity by co-entrapment of a surfactant

Getting a library of acids from a single molecule

Claudio Rottman et al, J. Am. Chem. Soc., 121, 8533 (1999); 123, 5730 (2001)

ET(30)

Getting a library of acids from a single molecule: ET(30)

Surfactant-dye interactions greatly enhanced in the cage

Hartley’s rule:

The most significant surfactant-induced changes in properties of charged dyes are observed when the charge of the dye is opposite to that of the surfactant

G. S. Hartley, Trans. Faraday Soc., 30, 444 (1934)

Getting a library of acids from a single molecule: ET(30)

Acid fuchsin – CTAB interactions

Solution pKi = 13

Huge pKi shift for AF: 8 orders of magnitude

Take-home message

Materials chemists:

“Don’t ask what chemistry can do for you, but what you can do for chemistry!”