Click chemistry &its application in material science

Presented by:

K.SASIDHAR

(Dr.K.V.S.N.Raju’s Group)

OCP Division,IICT

Concept of Click Chemistry

“Click chemistry” is a chemical philosophy introducded by K.Barysharpless in

2001, which describes the chemistry that can generate substances quickly and reliably

by joining small units together with high thermodynamic force.

Requirements for the click reaction are ,

The reaction must be

1. Modular

2. Wide in scope

3. High yield of product (nearly 100%)

4. Generate only inoffensive or no byproducts

5. Stereo specific

6. High atom economy

The process must be:

7.simple reaction conditions

8.readily available starting materials and reagents

9.simple product isolation by non-chromatographic methods

3

Defining a “Click” Chemistry Reaction

“ A click reaction must be modular, wide in scope, high yielding, create only inoffensive by-products (that can be removed without chromatography), are stereo specific, simple to perform and that require benign or easily removed solvent. ”

- Barry Sharpless

Kolb, H.C.; Finn, M.G.; Sharpless, B.K. Angew. Chem. Int. Ed. 2001, 40, 2004-2021.

Classes of “Click” Reactions

CYCLO ADDITION REACTIONS

NUCLEOPHILIC OPENING OF HIGHLY STRAINED RINGS

(like epoxides, aziridines cyclic sulphonates etc)

ADDITION REACTIONS OF ALKENES AND ALKYNES

(di hydroxylation of alkynes,

Thiol-ene reaction ,Michael addition etc)

Azide- Alkyne cycloaddition

Diels-Alder reaction

O

Nu

OH

Nu

R2

N N+ N-

R1N

N

N

R2

R1

R1

R2

R3

R4

R1

R2

R4

R3

R1 SH

R2

RS

R2

Non-Aldol type Carbonyl Chemistry(likethe formationof oxime ethers, hydrazones and aromatic heterocycles )

5

Historical Perspective of Azide/Alkyne Cycloadditions

L. Pauling. Proc. Natl. Acad. Sci. USA 1933, 19, 860-867; Huisgen, R. Angew. Chem. Int. Ed. 1963, 2, 633-696 Sharpless, K.B. et al. Angew. Chem. Int. Ed 2002, 41, 2596-2599; Meldal,M.J. et al. J. Org. Chem. 2002, 67, 3057-3064

R'' R'N3 N NN

R'

R''

1

5

+80oC N NN

R'

R''

1

4

+

R N3 R N N N R N N NH2R N N N

1933- Dipolar nature of azide first recognized by Linus Pauling

1960- Mechanism of 1,3-dipolar cycloaddition of azidesand alkynes pioneered by Rolf Huisgen

2001- Copper catalyzed 1,3-Dipolar cycloaddition by Sharpless/Meldal

R'' R'N3N N

NR'

R''

1

4

+ Cu(I)

rt

6

Copper Catalyzed Azide/Alkynes Cycloaddition (CuAAC)

• Thermodynamic and kinetically favorable (50 and 26 kcal/mol, respectively)

• Regiospecific

• Chemoselective

• 107 rate enhancement over non-catalyzed reaction

• Triazole stable to oxidation and acid hydrolysis

R'' R'N3

N NN

R'

R''

1

4

Cu(I)

+

Rostovtsev et al. Angew. Chem. Int Ed. 2002, 41, 2596-2599

7

CuAAC Catalytic Cycle

Himo, F. et al. J. Am. Chem. Soc, 2005, 127, 210-216.Ahlquist, M., Fokin, V.V. Organometallics 2007, 26, 4389-4391.

CuLxR'

N N N

R2

CuLx

HR'

CuLx

23 kcal/mol

18 kcal/mol

HR'

H+

CuLxR'

N N N

R2

CuLxR'

N N N

R2

CuLx

N N N

R1

R2

N NN

R CuLx

H+

N NN

R H

R2

R2

[CuLx]

RDS

8

Click chemistry Chemistry Applications in polymers

Some recent applications of click chemistry in material science are:-

• Adhesive polymers for Cu metal

• Potential Propellent binders

• polymer backbone modification

• Surface modification of nano particles.

• Hydrogels synthesis

• In hyperbranched polymers & dendrimers

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Adhesive polymes for Cu metal from click reaction

•David D. Diaz etal have recently synthesised a metal adhesive polymer based on copper catalyzed azide-alkyne cycloaddition.

• Di or tri azide and Di or tri alkyne monomers were introduced between copper or zinc plates,which provides necessary Cu(I) ions.

• The resulting adhesive polymer was found to possess comparable or superior adhesive strength to standard commercial glues.

HO

HO

N3

N3 N NN

NN

NN

N

NN

Npolymer

OH

HO

HO

HO polymer

polymer

OH

OH

• The above polymer is showing 268 ± 24 kg load per gram adhesive. where as commercial glue (weld-it) is showing 248 ± 111 kg load per adhesive.

Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 45, 5182–5189 (2007)

1,2,3-triazole-polymers as potential propellant binders

1. Propellant is the chemical mixture burned to produce thrust in rockets and

consists of a fuel and an oxidizer ,generally these are held together by polymeric

binder

2. Polyurethanes are well known binders for propellants. But there may be a chance

of side reactions during and after the polymerization ,that degrade the

mechanical properties of the resulting propellant .e.g., loss of elasticity

3. 1,2,3-triazole polymers are recently studied as novel binders for the explosives

and high energy propellants Because of high thermal & physical stability

4. Azide and alkynes monomers react readily and form polytriazole with out any

side reaction , o these are one of the best alternative for the propellant binders

5. A typical polyurethane, elastomeric linear matrix for rocket propellants has

modulus 0.05-1.9 Mpa

6. Where as the triazole polymers having much improved modulus 0.5-3.9 MPa

7. the mixture of above cross linked polymer with 43wt% aluminum filler greatly

improve the modulus of the triazole polymers, which could reach nearly 4MPa.

Ling Wang et.al.,Journal of AppliedPolymer Science, Vol. 117, 2612–2621 (2010)

Polyurethane backbone modification by click chemistry

• Du Prez et al. synthesized linear polyurethanes (PUs) having alkyne groups• located along the backbone

• The polyurethane was formed by reacting with two• different alkyne-functionalized diols with a diisocyanate compound

• TGA measurements demonstrated that the incorporated triazoles in the PU materials strongly improves the final char yield

Surface modification of silicaNano particles through ‘click’ chemistry

Any particle with a size from 10 nm to 100nm is generally termed as nano particle.

Nano particles have many applications. ex:- colloidal gold – useful to stain the glass with an intense red colour ,was done in ancient

times.Zinc nano particles are used in the sun block creams and cancer medicine.Silica nano particles in chromatography, bio-seperation, imaging, and multifunctional

nano comopostes. surface modification of silica nano particles by click chemistry:- functionalisation of nano particles can be achieved by so many ways. But silane

coupling agents are widely used to surface modification of silica nano particles.But it has some drawbacks such as,solvent polarity and reaction temperature. in large

scale surface capping is not uniform.Click reaction is one of the efficient way to impart desirable funtionalities to nanoparticles

without any side reactions.Ex:-pyrene, a fluorophore (which shows excimer emmision) is successfully attached to the silica nano particles.

CURRENT SCIENCE, VOL. 95, NO. 9, 10 NOVEMBER 2008

Hydrogels synthesis from click chemistry

• Hydrogels are Water swollen crosslinked polymers• Crosslinks may occur:

– by reaction of one or more monomers– hydrogen bonds– Vander Waals interactions

• Hydro gels traditionally prepared by photo polymerization of water soluble vinyl monomers, such as polyethylene glycol- diacrylates, but has some defects like uncontrollable crosslinking

• click chemistry concept is utilized In designing controlled hydro gel networks With improved properties.

• Another advantage of click chemistry is hydrogels can be prepared at room temperature.

Dendrimershyper branched

polymers

1.Dendrimer = Greek words dendron (tree)+ meros (part)

2.Made in a very sophisticated fashion [ Divergent and convergent process]

3.Perfectly built onto a core molecule

4.Monodisperse [ Mw =Mn] and high degree of branching ( DB =1 )

5.They are symmetrical and layered macromolecules

6.These polymers consist of three distinct areas : polyfunctional central core ( center of symmetry); radial symmetrical layers of repeating units( generations); end standing groups (terminal groups).

1.Made in a very easy fashion [ Divergent and convergent process

2.polydisperse [ Mw>Mn] and less degree of branching ( DB >1 )

3.They are an irregular macromolecules

4.These polymers structure consist of three distinct groups : dendritic groups ;linear groups and terminal groups.

Examples of hyper branched polymers:

Boltorns (P( bis -MPA) hyper branched polymer),

Hybranet (poly(ester amide))

poly( phenylenes )

Hyper branched Polymers & dendrimers from Click Chemistry

Dendrimers and hyper branched polymers are synthesized mainly two ways

• Divergent strategy:- Core to Surface

• Convergent strategy :-Surface to core

Click chemistry is also an efficient reaction to produce dendrimers and hyperbranched polymers with good yeilds

Convergent Approach Divergent approach