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1. Transition Metal Based Chemistry
2. Main Group Chemistry
3. Stochastic Simulations
4. Ab Initio molecular dynamics by nanoreactor approach
5. Non Covalent Interactions
Transition Metal Based Chemistry:
A lot of exciting chemistry is being done today through the assistance of organometallic complexes: complexes that contain a transition metal.
Many important chemical transformations have become possible through the mediation of such complexes. However, there is a lot that is
unknown about this chemistry.
Sometimes, the nature of the active species may not be clearly known, or the mechanism by which the complexes effect the catalysis
or transformations may not be fully clear. This is where computational methods based on quantum chemical approaches, such as density
functional theory (DFT) are very important. A lot of information with regard to the transition metal based systems is not possible to obtain
through experimental methods, and so one has to take recourse to computational approaches in order to get insight into these systems.
This is what groups like ours attempt to do. We have worked on important organometallic systems, such as the rhodium complexes
employed for hydroformylation catalysis, or the early transition metal based systems that have been employed for Ziegler Natta olefin
polymerization catalysis.
Hydroformylation Catalysis with Rhodium Complexes :
Currently our group is working on industrially important homogeneously catalyzed reactions such as Hydroformylation and Homogeneous
Ziegler-Natta olefin polymerization. Our research interest is to find the activity differences between different catalysts and give an insight
into the catalysis process. Moreover, Our goal is to predict highly active and selective catalysts for the catalysis using Density Functional
Theory (DFT) calculations.
Our interest is to find the highly active and selective catalyst for hydroformylation. We use DFT as a tool to investigate entire hydroformylation
cycle ( Heck-Breslow mechanism an widely accepted mechanism for hydroformylation) for the different experimentally tested catalysts. Such
studies can give an insight into the hydroformylation processes and predictions can help to improve the catalysis process.
References:
2. Sparta, M.; Børve, K. J.; Jensen, V. R.
3. Diebolt, O.; Tricas, H.; Freixa, Z.; van Leeuwen, P. W. N. M.
4. Meeuwissen, J.; Sandee, A. J.; de Bruin, B.; Siegler, M. A.; Spek, A. L.; Reek, J. N. H.
Ziegler-Natta Catalysis:
MgCl2 supported heterogeneous Ziegler-Natta (Z-N) catalysis is one of most important chemical processes for the olefin polymerization.
It is responsible for the production of millions of tons of polyethylene and polypropylene in the form of rubbers, plastics and elastomers.
Owing to multi component system the actual role of each components is still unknown. The components are TiCl4: catalyst precursor,
MgCl2: catalyst support and AlR3 catalyst activator). The oxygen containing Lewis base "donor" has also been accepted as the fourth
component in Z-N catalyst
Our main focus in this field to check the effect of donors in the Z-N catalysis. In our first study we showed the nature of active
sites in Z-N olefin polymerization catalyst, along with this effect of different class of ester donors on the active site has also
been studied. It has found that presence of donor increase the polymer productivity with increase the activation gap between
the insertion and termination processes.
European Journal of Inorganic Chemistry 2014, 2014, 5063.
In second study we showed that along with olefin polymerization reaction, unwanted side reaction can also take place
which leads to the donor decomposition. In this study, first time we showed the reaction mechanism of how catalyst could
decompose the ester donors.
Organometallics 2014, 33, 4357
Water Gas Shift Reaction (WGSR) :
Here we have investigated the possibility of metal-metal cooperativity in improving the yield of homogeneous water gas shift reaction
The quantum mechanical as well as energetic span model (ESM) calculation indicate that bimetallic catalysts would be likely to be more
highly active than mononuclear metal based catalysts for the WGSR.
Late transition metal complexes as fustrated Lewis pair :
A modified palladium complex has been considered in this regard as an example of a potential late transition metal FLP and studied
with full quantum mechanical calculations. The calculations indicate that this complex would be effective at catalyzing ammonia borane
dehydrogenation. The possibility of competing side reactions such as reductive elimination have also been considered, and it has been
found that such processes would also yield stable products which could act as an FLP in catalyzing reactions such as the
dehydrogenation of ammonia borane. The current work therefore expands the scope of metal containing FLPs to include late transition
metals and demonstrates computationally the potential of such complexes for exhibiting metal–ligand cooperativity.
A.Pal and K.Vanka, Dalton Trans., 2013,42, 13866-13873.
Main group chemistry:
small molecule activation
Small molecules are generally abundant in earth and thermodynamically stable. The activation of small molecules like H2, O2,
H2O, NH3BH3 are important in various industrial and biological applications such as NH3 synthesis, Hydrogen Economy, nitrogen
fixation etc. The activation of these molecules needs efficient catalytic systems to improve the yield of the reaction. Even though the
traditional heterogeneous catalyst systems pioneered in this area, recent developments proved that homogeneous catalyst are very
efficient and it require mild temperature and pressure conditions to carry out the reaction.
We are working on various homogeneous organometallic and main group catalyst systems to explore its potential to activate
small molecules such as H2, CO2, NH3BH3. Density functional theory is employed for the computational investigations, since
DFT is recognized as an important method to provide reliable results for the reaction mechanisms. some of the interesting results
based DFT study involve the utilization of phosphorus incorporated organic cages and Ga-N molecular cages for the catalysis of
ammonia borane (AB) dehydrogenation,possibility of metal-metal cooperativity in the homogeneous water gas shift reaction.
Porous Cages:
one dimensional porous cage
A detail density functional theory (DFT) study indicates that one dimensional porous cage containing main group
elements (Carbon-Nitrogen) which are sterically precluded, can act as frustrated lewis acid-basic pair. Thus it can
generate hydrogen gas by dehydrogenating the ammonia borane.
Study showed that a replacement of nitrogen with phosphorus can improve the catalytic system. The main
advantage of such kind of cage system is, there are several (12) similar sites for the catalysis. We have shown
that a simultaneous multi-site catalysis can be done by such porous cages.
A.Pal, K.Vanka Chem.Commun., 2011, 47, 11417-11419.
Ga-N molecular cage:
Here we introduced a new concept in the field of small molecule activation: the use of molecular
cages containing only main group elements as the catalyst for mediating the activation of small
molecules like NH3BH3.
The strategy used here is to exploit the “opening” and“closing” of labile bonds in molecular cages for activating the desires bond
in the small molecules. Full quantum mechanical calculations employing DFT/SCS-MP2 methods indicate that recently synthesized
Ga−N cage compounds are effective candidates for dehydrogenation of AB.
N.Kuriakose; K.Vanka Inorg.chem., 2013, 52 (8), 4238-4243
Silylene can rival transition metal systems
Full quantum chemical calculations with density functional theory (DFT) show that bond-strengthening back-donation to a
π-diborene, recently discovered for transition metal systems (Braunschweig and co-workers, Nat Chem., 2013, 5, 115),
would be just as favored for Main Group silylene complexes. This result not only shows the range and applicability of the
bond-strengthening back-bonding interaction, but also showcases the capacity of silylene complexes to do new chemistry,
such as the cooperative activation of carbon monoxide and carbon dioxide.
A.Pal and K.Vanka, Chem.Commun., 2014, 50, 8522-8525.
Stochastic Simulations: The Development Of New Methods
The traditional view of modelling the time evolution of the chemical species in a given reaction network is based on solving
the reaction rate equations. But, this deterministic approach fails to take into account the inherently stochastic behavior of cellular
systems due to the presence of small number of molecules. Thus to take into account, the fluctuations as well as the discreteness of the
molecules a kinetic Monte Carlo based probabilistic model
However, due to the occurrence of a single reaction in each time step the simulation performed by the SSA is computationally
expensive. In order to solve this problem, several approximate stochastic simulation methods have been proposed. This methods have been quite
successful in simulating the time behavior of the chemical species while retaining the required accuracy. In case of such approximate methods,
it is also found that they may give rise to unrealistic (negative) numbers during the simulations. The workers in this field have tried to solve this
issue by using different strategies.
We have come up with an approximate accelerated stochastic simulation method to address the issue of the computational time associated
with the SSA. (S. Kadam and K. Vanka, J.Comput.Chem 33, 276 (2012))We have also proposed a new method to solve the problem of
negative numbers occurring during the simulations(S.Kadam and K.Vanka, J.Comput.Chem. 34, 394 (2013)) . This newly proposed method
is termed as Representative Reaction approach (RRA).
Ab Initio molecular dynamics (AIMD) by nanoreactor approach
Experimenal chemistry often plays the principal role in discovering new compounds and proposing new reaction mechanisms,
and computational chemistry provides valuable support by arbitrating between competing proposed mechanisms. Recent algorithmic
and computational advances, including those that leverage graphics processing unit (GPU) architectures, could open the
door to using computation not only to arbitrate different hypotheses, but also as a discovery tool to reveal new fundamental chemical
mechanism.On the other hand ab initio nanoreactor makes a bridge between expeimental and theoretical chemistry
The ab initio nanoreactor—a highly accelerated first-principles molecular dynamics simulation of chemical reactions that discovers new
molecules and mechanisms without preordained reaction coordinates or elementary steps .
Nanoreactor dynamics simulations involve the use of spherical boundary conditions, but also the use of a virtual piston to
accelerate reactions. This “piston” is accomplished through the use of time-dependent spherical boundary conditions .
This ab initio nanoreactor method is only implimented in TeraChem quantum chemistry and AIMD software packages by
Todd J. Martínez and his group. Using the nanoreactor, they showed the new pathways for glycine synthesis from primitive compounds
proposed to exist on the early Earth, which provide new insight into the classic Urey–Miller experiment.
Ref: Todd J. Martinez et.al , Nature Chemistry, 1044-1048 , 6 ,2014
Currently,we are working with nanoreactor approach for prebiotic systems using Terachem software and to analysis it.
Non-Covalent Interactions:
Noncovalent interactions are of great significance in several areas of chemistry and biology. There has been a conscious effort in recent
times to exploit such interactions in order to achieve specifically designed goals. However, in order to fully unlock and exploit the
potential of such noncovalent interactions, it is necessary to properly understand the factors that determine their strength. It is well
established in literature that these interactions are dominated by the electrostatic contributions in several different families of complexes.
What has also become accepted is the long range impact of secondary electrostatic interactions in such complexes.
Our research focuses upon the directional nature of secondary electrostatic interactions, by computing electrostatic force, rather than
energy, an aspect that has been totally overlooked so far in the literature. We look further to exploit directional long range secondary
forces in rational designing of new systems where the binding strength
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