Fine tuning of catalysts

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Seminar by:-
M. Sameer Reddy
M.Phil. in Chemical Sciences
II Semester
School Of Chemical Science
Central University Of Gujarat

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OUTLINE OF TODAY’S DISCUSSION
 TERMS AND THEIR DEFINITIONS
OF THE DAY
 NEED AND AIM FOR FINE
TUNING.
 TRACING THE ORIGIN OF FINE
TUNING
 MULTIFUNCTIONAL CATALYSTS
 MULTICATALYSIS : SUPRA
MOLECULAR APPROCH
 LETS EXAMINE THE ENZYMES
 ARTIFICIAL ENZYMES?
 CONCLUSION; WHAT CAN WE

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Terms and their definitions for the Day:-
 Homgenus catalysis:- Both the substrate and the catalysts are
in the same phase.
 Organocatalysts:- Using metal free small organic molecules
such as thiourea, L-proline etc.., as catalysts
 Supra molecular chemistry:- “Chemistry beyond molecules
or chemistry of non-covalent forces or study of host guest
interaction through non-covalent interactions”.
 Fine tuning:- Making small adjustments for optimal
performance or effectiveness.
 Tandem synthesis:- A tandem reaction is a consecutive series
of intramolecular organic reactions which often proceed via
highly reactive intermediates. It allows the organic synthesis of
complex multinuclear molecules from a
single acyclic precursor.
{Ref:- Graham L. Simpson, Timothy P. Heffron, Estíbaliz Merino,
and Timothy F.. J. Am. Chem. Soc. 2006, 120 (4) 1056–1057}

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Continue;
Multifunctional catalysts:- A single molecule with two or more
functional groups, each one having a different catalytic
activity, is a multifunctional catalyst.
Ref:-
Sung Hun Sang Ho Oh,a Ho Sik Rho, Je Eun Lee, Ji Woong Leea and Choong
Eui Song ;Chem. Commun., 2009, 2220–2222
Multicomponent catalysts:- The use of distinct non-covalently
bound catalysts two (or more) chiral units. It is devoid of complex
procedures to produce a compatible catalyst like multifunctional.
Ref:-
Matthew L. Clarke* and Jos A. Fuentes; Angew. Chem. Int. Ed.
2007, 46, 930 –933

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Need And Aim Of Fine Tuning Of catalysts
Need:-
The synthesis of catalyst itself is costlier; hence
recyclability is becomes important for economic
reasons.
In organocatalysts, though many molecules used are
cheap and easily available, the catalytic loading is
higher and the ee% and yield are between average to
good.
Aim:-
to overcome the above mentioned short comes
and to develop use them in multiple reactions i.e. in
on pot and tandem synthesis protocols.

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Tracing Origins Of Fine TuningTracing Origins Of Fine Tuning
Fine tuning can be as simple as
covalently joining a group to the
catalyst to much more sophisticated
systems like:-
•dendrimer loading (ref .cont;2)
•Loading on to polymers or any
other recyclable inert support.
•multifunctional catalytic systems.
•multicomponent catalytic systems.
Fine Tuning Initial Example:- Grubs Catalyst And Proline Derivatives In VariousFine Tuning Initial Example:- Grubs Catalyst And Proline Derivatives In Various
ProcessesProcesses

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Merrifield resin supportedMerrifield resin supported
prolineproline
G2- diaminobutane poly(propyleneimine)G2- diaminobutane poly(propyleneimine)
dendrimers DAB(AM) with proline on peripherydendrimers DAB(AM) with proline on peripheryContinue:-
Dendronizing Process of the Silica-Coated Magnetic NanoparticlesDendronizing Process of the Silica-Coated Magnetic Nanoparticles

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Multifunctional CatalystsMultifunctional Catalysts
A single molecule with two or more functional
groups, each one having a different catalytic activity,
is a multifunctional catalyst
or
Placing different functional moieties on a support
to perform multiple catalytic activity.
the idea originates from the modelling of enzyme
active site.
The placing of Lewis acid or base with Bronsted
acid or base coupled in chiral environment.an ideal as
all four of them.
Eg 1):- Bifunctional Chiral Phosphine Catalyzed Aza-MBH Reaction

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Eg 2):- Asymmetric Bifunctional Catalyst Made Of Rare Earths And Alkali
Metals

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Multicatalysis: SupramolecularMulticatalysis: Supramolecular
ArrangementArrangement The non-covalent association of both chiral and/ achiral molecules to control and
perform the enantioselective and yield optimized reaction.
 It has the advantage over multifunctional catalysis is ease in generation of library
asymmetric catalysts with simple and cheap monomer units.
E.g. 1) nitro Michael
addition/asymmetric
reduction
E.g. 2):- Asymmetric hydrogenation; M= Ru

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Comparison of
multiple and multi
functional catalysis

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Lets Examine The EnzymesLets Examine The Enzymes
Enzymes are active proteins involved in
biological catalytic activity.
The chiral environment produced by large
peptide backbone, gives it asymmetric
capabilities.
Previously mentioned both multiple
component and multifunctional activities are
seen in the enzymes at very mild conditions.
Yet we lack the exact mechanism of many
enzyme action. Hence still there is no
attempt yet for producing completely
functional replica of any enzyme.
How can we probably replicate?
May be with chiral dendrimer made of amino
acids!

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Enzymatic Cycle OfEnzymatic Cycle Of
TyrosinaseTyrosinase
Ref :-Olivares & Solano; Pigment
Cell Melanoma Res. 22; 750–760

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• There are examples of peptide
dendrimers which are involved in
catalysis as such. But their activity
is low and mostly used in
hydrolysis reactions.
• It seen that even a fractional
section of active site is reproduced
the catalytic activity is observed.
• A multifunctional and a
multicomponent catalytic
environment can be fit into this
kind of dendrimers, because they
are rigid and have the tendency to
support multiple non-covalent
interactions.
• Once the activity is established,
there can be investigations to
develop to recycling strategies.
Peptide dendrimers G1-G4 with iterations of a (His- Ser)2Dap dendron;Peptide dendrimers G1-G4 with iterations of a (His- Ser)2Dap dendron;
ARTIFICIAL ENZYMES??ARTIFICIAL ENZYMES??

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Conclusion:- What CanConclusion:- What Can
We ExpectWe Expect
 It can be concluded from the above that :-
1. Enzyme mimicking is the future of homogenous
catalysis.
2. Above mentioned examples are an approach to
understand and replicate the enzyme efficiency.
 The study of this kind though started in 1990; the
critical evaluation started in around 2004!!
 Most interesting out come of the series is the increase
in one pot synthetic protocols trying to replicate
enzymatic type conditions.
 There is need to add another dimension to the above
mimicking efforts i.e., Recyclability.
 There are already efforts going on to recycle and
reuse the catalyst, leading to continuous flow systems
which would save energy, environment and cost.

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ReferencesReferences1. Fine-Tuning Ligands for Catalysis Using Supramolecular Strategies;
J. N. H. Reek et al.; Eur. J. Inorg. Chem. 2007, 4653–4662
2. Self-Assembly of Organocatalysts: Fine-Tuning Organocatalytic
Reactions; Matthew L. Clarke* and Jos A. Fuentes; Angew. Chem. Int.
Ed. 2007, 46, 930 –933.
3. Asymmetric Bifunctional Catalysis ;Shibasaki et al; acc. chem. res. Vol.
42, 8, 2009 ,1117-1127
4. Multifunctional Chiral Phosphine Organocatalysts; Wei and Shi;
acc. chem. res. 2010 Vol. 43, No. 7, 1005-1018
5. Asymmetric Supramolecular Catalysis: A Bio-Inspired Tool for the High
Asymmetric Induction in the Enamine-Based Michael Reactions; D. B.
Ramachary et al; Chem. Eur. J. 2012, 18, 8008 – 8012.
6. Multiple Catalysis with Two Chiral Units: An Additional Dimension for
Asymmetric Synthesis; M. Bella et al. Angew. Chem. Int. Ed. 2011, 50,
6216 – 6232
7. New directions in supramolecular transition metal catalysis; ; Reek.et al
Org. Biomol . Chem . , 2005, 3,2371 – 2383.
8. A polymer-supported Cinchona-based bifunctional sulphonamide catalyst :
a highly enantioselective, recyclable heterogeneous organocatalyst;
Choong Eui Songet et al; Chem. Commun., 2009, 2220–2222

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1. Organocatalytic Biomimetic Reductions; Ramachary and Kishor J.
Org. Chem. 2007, 72, 5056-5068.
2. Proline-modified poly(propyleneimine) dendrimers as catalystsfor
asymmetric aldol reactions; E. Bellis, G. Kokotos / Journal of
Molecular Catalysis A: Chemical 241 (2005) 166–174
3. Metal Supported on Dendronized Magnetic Nanoparticles:
4. Highly Selective Hydroformylation Catalysts ; J. Am. Chem. Soc.
2006, 128, 5279-5282.
5. Darbre and Reymond; Acc. Chem. Res. 2006, 39, 925-934
6. Wikipedia.org
7. Organic chemistry.org
CONTINUE
;

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Fine tuning of catalysts

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