Summary of the Original Research Contributions of Dr. Suresh C. H., Principal Scientist, Inorganic &
Theoretical Chemistry Section, CSIR-NIIST, Trivandrum
The central theme of Dr. Suresh's research is understanding molecular reactivity through
theoretical and computational modeling of the structure and bonding in molecules, reactions and
intra- and intermolecular interactions. His formal training in this field started when he joined the
group of Prof. S. R. Gadre for Ph.D. who was at that time Professor of Chemistry at the University of
Pune. Under Prof. Gadre's guidance, he completed the Ph.D. in 1999 and the title of his thesis was
'Exploring QSAR, Aromaticity and Ion-pair Formation via Molecular Electrostatics'. Among the 12
papers published during Ph.D., he contributed significantly to the original ideas portrayed in many of
them. Among them the paper that interprets Clar's aromatic sextet theory using molecular
electrostatic potential (MESP) could be rated as the most important which was published in J. Org.
Chem. (Vol. 64, 1999, pages 2505-2512, citations 81). This paper gave a firm theoretical basis for the
empirical rules proposed by Clar for interpreting the aromatic character of fused benzenoid
hydrocarbons.
Aromaticity is one of the central themes in organic chemistry to describe molecular
reactivity. Suresh kept his interest in this topic even after Ph.D. and wrote many significant papers
during his post-doctoral period as well as during his independent career that started in CSIR-NIIST in
2005. He derived a QSAR relationship using the MESP based quantum chemical descriptor to predict
the carcinogenic activity of polycyclic aromatic hydrocarbons and their diol-epoxides. Also using
MESP plots, a pictorial representation and validation of Clar's aromatic sextet theory was made for a
large number of condensed aromatic molecules. Very recently, he used the Clar's aromatic sextet
theory to design multi-topic N-heterocyclic carbene ligands and predicted that aromaticity can
stabilize a ligand with four carbene centers. He devised a radical based homodesmic reaction
scheme to determine accurate values of aromatic stabilization in a large spectrum of molecules
including heterocyclic systems. He also applied aromaticity as a decisive factor to describe the
mechanism of some intriguing organometallic reactions. Among them, the paper with the title
'Aromaticity-driven rupture of CN triple and CC double bonds' described the mechanism of an
uprecedented reaction between Cp2Ti(C4H4) and RCN leading to benzene and pyridine and showed
that aromaticity was the driving force for the reaction leading to highly exothermic products. Very
recently, Suresh described the mechanistic pathways for a Ru(II)-catalyzed autotandem reaction for
the formation of imine and hydrogen from alcohol and amine based on several aromatizationdearomatization steps. Suresh also supported the experimental work of Prof. T. K. Chandrashekar for
the study of aromaticity in extended porphyrin systems (papers mentioned in this paragraph are
publihshed in journals such as JACS, Chem. Eur. J., Chem. Comm., J. Org. Chem., Organometallics, J.
Comput. Chem., Chem. Asian J., Org. Biomol. Chem., New. J. Chem., Chem. Phys. Lett.)
Suresh made significant contributions in the area of organometallic chemistry while working
in the group of Prof. Nobuaki Koga at Graduate School of Information Sciences, Nagoya University,
Japan who was his postdoctoral mentor during the period 2000-2004. Prof. Koga, a well-known
theoretical organometallic chemsit, who studied in the group of Nobel Laureate Prof. K. Fukui and
also in the group of Prof. K. Morokuma gave full freedom to his research activities and guided him
to master transition state modeling. Hence, in almost all the papers publihsed from Koga's group,
original contribution from Suresh was significant. During this period, he studied the mechanism of
several interesting organometallic reactions, particularly the complexes of titanium, iron, ruthenium,
cobalt and rhodium. One of the most significant contributions of Suresh comes from his attempts to
apply the MESP topography analysis that he learned from Prof. Gadre's group to organometallic
chemistry. He was the first to apply this method to an organometallic complex, the (arene)Cr(CO)3 to
describe the bonding features and reactivity of the complex. He also applied MESP analysis to derive
atomic radii, electronegativity of atoms and group electronegativity of functional groups (papers
mentioned in this paragraph are publihshed in journals such as JACS, Inorg. Chem., Organometallics ,
J. Phys. Chem A).
One of the most noted contributions of Suresh from the group of Prof. Koga is on the
mechanistic work he carried out on ruthenium-catalyzed olefin metathesis. He showed that unique
orbital interactions exist in the key intermediates of olefin metathesis which explained the unusually
long Csp3-Csp3 bonds in ruthenacyclobutanes as well as the very low activation barrier for the CC bond
cleavage. The paper is regarded as a fundamental paper in the area of CC bond metathesis
(Organometallics, 23, 2004, 76; citations 84). In 2004, Suresh moved to Indiana University,
Bloomington in the group of Prof. Mu-Hyun Baik and stayed with him for about seven months. Prof.
Baik allowed him to pursue his interest in olefin metathesis. They together publihsed a paper in
Dalton Trans. which gave a detailed description of the orbital interaction diagram for the Grubbs
olefin metathesis intermediate. This work confirmed that a new type of CC agostic bonding exists in
the Grubbs intermediate that led to strong activation of the CC bonds leading to metathesis
reaction. Suresh also publihsed a paper in Organometallics from CSIR-NIIST which showed that
agositc interaction is the main driving force for the degradation of the Grubbs second-generation
metathesis catalyst. Later, in a single author paper (J. Organomet. Chem.), Suresh showed that CC
agostic interaction is a common phenomenon in a variety of transition metal olefin metathesis
catalysts including that of Schrock catalyst. This work confirmed that -carbon of the
metallacyclobutane has hypervalent character (five bonds) due to its significant bonding interaction
with the metal center.
Very recently Suresh explored the structure and bonding in alkyne methesis intermediates.
From CSIR-NIIST, he proposed research in this area to Humboldt foundation in 2009 to obtain the
fellowship for experienced researchers. The fellowship enabled him to work in the group of Prof.
Gernot Frenking, a renowned theoretical chemist at Marburg University, Germany. Along with Prof.
Frenking, he publihsed as corresponding author three significant papers in Organometallics. These
papers showed that metallacyclobutadienes (the key intermediates of alkyne metathesis) of group 4,
5 and 6 possess a unique metal to -carbon -bonding interaction. The significant bond order
between metal and C explained the short M-C distance as well as activation of the CC bonds. This
type of 1,3-interaction responsible for the M-C bond is unprecedented in organometallic chemistry.
Suresh's efforts clearly proved that the 1,3-MC interaction is a unique bonding scenario in
organometallic chemistry which gives the unusual planar tetra-coordinate character to the -carbon.
His extensive theoretical studies on several complexes proved the formation of 1,3-MC bond and
were further confirmed by strongly correlating the theoretical findings to the X-ray crystallography
data of metallacyclobutadienes. In his third paper with Prof. Frenking, he showed that 1,3-MC
bonding interaction can be gainfully used to design 'edge complexes' in organometallic chemistry as
this work described the formation of metal carbon bonds at the V-shaped edges of condensed
aromatic hydrocarbons.
Suresh's attempts to apply MESP topogrpahy analysis to study organometallic reactivity led
to several significant contributions. Among them the most cited article is the one he authored with
Prof. Koga and entitled 'Quantifying the electronic effect of substituted phosphine ligands via
molecular electrostatic potential' (Inorg. Chem.2002, 411, 573, citations - 82). Later from CSIR-NIIST,
he published a single author paper which described the steric effect of phosphine ligands in
organometallic chemistry (Inorg. Chem. 2006, 111, 710, citations - 60). His efforts to describe the
steric and electronic effects of phosphine and N-heterocyclic carbenes based on MESP topography
have been noteworthy and they led to two well cited publications in Inorg. Chem. and one in J. Org.
Chem. Further, he demonstrated the use of MESP based approach to understand the
stereoelectronic features in the mechanism of Grubbs first and second generation olefin metathesis
catalysts (three publications in Organometallics). Recently Suresh applied MESP based and electron
density based descriptors to derive multiple linear regression equations to quantify trans influence
in organometallic and inorganic complexes. His findings were published as three articles in Inorg.
Chem. and one in Dalton. Trans.
Among the other major contributions, the most noted one is his studies on substituent
effects in organic chemistry. Two significant papers in this area were written during his Ph.D. period
with Prof. Gadre; one in JACS (62 citations) and another in J. Org. Chem. (46 citations). Suresh and
Gadre were the first to show a strong linear correlation between the MESP minimum on aromatic
ring and substituent Hammett constant and a consolidated paper in this topic was published from
CSIR-NIIST in 2007 in J. Phys. Chem. A (citations 54). During his career at CSIR-NIIST, Suresh wrote
several well cited papers in this area and the titles of the papers are (i) Accurate prediction of cationpi interaction energy using substituent effects, (ii) Resonance enhancement via imidazole
substitution predicts new cation receptors (iii) NMR characterization of substituent effects in cationpi interactions, (iv) Substituent effects in cation-pi interactions: a unified view from inductive,
resonance, and through-space effects, (v) Quantitative assessment of substituent effects on cationpi interactions using molecular electrostatic potential topography, (vi) Appraisal of through-bond
and through-space substituent effects via molecular electrostatic potential topography, (vii)
Quantification of substituent effects using molecular electrostatic potentials: additive nature and
proximity effects, (viii) An electrostatic scale of substituent resonance effect, (ix) Use of molecular
electrostatic potential for quantitative assessment of inductive effect. Among these papers six were
published in J. Phys. Chem. A, one each in New J. Chem., Chem. Phys. Lett. and Tetrahedron Lett.
In a very recent paper published in J. Phys. Chem. A (2014), Suresh has shown that a large
variety of hydrogen, halogen and dihydrogen bonds can be defined as electron donor-acceptor
interactions and also derived a linear equation to correlate the electron donor-acceptor power of
the contributing atoms of these non-covalent bonds and the interaction energy. This paper gave
significant new insights in to the non-covalent bonding in chemistry. It was rated as the top 1 most
read articles in J. Phys. Chem. A. In yet another recent work (Phys. Chem. Chem. Phys., 2014), Suresh
showed that lone pair-pi interactions in chemistry can be described in terms of the molecular
electrostatic potential of the lone pair bearing atom of the molecule. Further, he predicted that
fluorinated aromatic scaffolds are ideal for the synthesis of sensors for trapping weakly binding lone
pair bearing molecules and anions (one of the most read articles, J. Phys. Chem. A, 2014). Suresh
and Gadre teamed up recently to write one of the fundamental papers in chemistry which entitled
as 'Lone pairs: an electrostatic viewpoint' described the characterization and quantification of lone
pairs in molecules based on MESP topography. This paper published in J. Phys. Chem. A (2014) is
rated as one the most read articles of that journal in the last 12 months.
Suresh has been prolific in publishing papers that dealt with mechanism of numerous
intriguing reactions in organic and organometallic chemistry. He contributed significantly to
understand the regeoselectivity in Markovnikov's addition reaction (contribution from Ph. D. work),
Grubbs olefin metathesis reaction, Schrock alkyne metathesis reaction, ruthenium(II)-catalyzed
water splitting reaction, CO2 fixation reaction, Stetter reaction, cycloaddition reaction,
stereoselective reactions, migration-, oxidative addition- and reductive elimination reactions in
organometallic chemistry, radiation reactions and photochemical reactions. Theoretical
investigations of Suresh have also provided key chemical insights to several experiments and those
were done in collaboration with experimentalists from India and abroad. The prominent among
them with significant theoretical contributions are Organometallics, 23, 2004, 117; Tetrahedron, 62,
2006, 605; J. Phys. Chem. A, 110, 2006, 4329; JACS. 128, 2006, 16083; Tetrahedron, 63, 2007, 1617;
JACS. 129, 2007, 9439; J. Phys. Chem. A, 2007, 111, 12839, Chem. Eur. J. 14, 2008, 5851.
In summary, Dr. Suresh's contributions in understanding molecular reactivity and reactions
in organic and organometallic systems are noteworthy. He made significant new contributions in
several areas of reactive chemistry and published 125 papers. Among them the most noteworthy are
the contributions in areas such as metathesis reactions, substituent effects in organic chemistry,
stereoelectronic effect of ligands in organometallic chemistry, aromaticity, metal-organic
transformation reactions, stereo- and regio-selective organic reactions, non-covalent interactions
and agostic interactions. At present his h-index is 28 and the total citations is 2207 (data from Web
of Science).