Archives

Graduate Student

Andino Martinez, Jose Guillermo

Biography

I was born in San Salvador, El Salvador one morning of Feb 1974. From 1992 I attended the University of El Salvador at the School of Chemistry and Pharmacy for three years. After my third year I became an undergraduate Fulbright scholar and came to the University of Louisville, Kentucky where I graduated with a BS in Chemistry with concentration in Biotechnology. After one and a half years working in El Salvador I returned to Louisville for my PhD under supervision of Prof. Dorothy Gibson. For my thesis work I focused on the synthesis of Ru polypyridyl complexes that were proposed intermediates in electrochemical reductions of CO2. During this time I developed a deep interest in the area of small molecule activation for energy conversion purposes. After finishing my PhD, I continued to work in the labs of Prof. Gibson for almost two years and in June 2007 I joined the research group of Prof. Mu-Hyun Baik as a postdoctoral researcher. I have worked on the computational analysis of proposed CO2 catalysts to intelligently design the next best catalyst with the goal of using CO2 for the synthesis of fuels. More recently I have started collaborations with Prof. Kenneth Caulton and Prof. Daniel Mindiola for quantum chemical modeling of their chemical reactions.


Research Projects

In the Caulton group I have applied DFT to determine the mechanism of reaction of highly reactive (PNP)M-L (PNP = (tBu2PCH2SiMe2)2N-;  M = Ni, Rh, Os; L = H, no ligand) complexes with H2, O2, CO2 and other substrates. For example, there are no complexes of the intact molecule H2 attached to a Ni(II) center, yet experiments under way at IU have now detected one.

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Questions I am trying to answer are how is this H2 bound to nickel, what is its energy of dissociation, and what follow-up reaction might this species do?  Another unprecedented molecule made by Nick Tsvetkov in the group is (PNP)RhO; this too reacts with H2, to form simply coordinated water!

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Mechanistically, how does H2 attack this molecule?  Is there ever a Rh/H bond formed in any intermediate, or does H2 truly attack directly on the oxo ligand?

Quite different reactivity is the condensation of CO2, my favorite molecule, with (PNP)RhO.  This forms a carbonate complex, whose geometry I have established by DFT calculations, but what is its mechanism of formation?

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In favorable cases, the results of my calculations challenge the experimentalists to do new hypothesis-testing studies, often at low temperature.

Lab Member

Nobuyuki Komine

Biography

Nobuyuki Komine was born and grew up in Tokyo, Japan. He received his Ph.D. in March 1998 under the supervision of Professor Takeshi Nakai and Dr. Katsuhiko Tomooka at the Tokyo Institute of Technology. He joined the S. Komiya and M. Hirano research groups in Tokyo University of Agriculture and Technology (TUAT) as a Research Associate in April 1998. He became an Assistant Professor of TUAT in 2007. In April 2011, he joined the Caulton and Mindiola groups as a Postdoctoral Fellow working on C-H and C-C bond insertion chemistry involving coinage metal catalysts.


Research Projects

Alkanes are compounds of carbon and hydrogen atoms constructed by only C-C and C-H single bonds. The simplest and most abundant is methane, the primary constituent of natural gas. The use of alkanes as environmentally benign feedstock for clean-burning fuels and a host of petrochemicals is a high impact goal. The development of a new catalyst for selective, direct alkane functionalization could lead to a new paradigm in petrochemical technology that is environmentally cleaner and economically superior. In our research group, the reaction where insertion of the carbene derived from N2C(H)(CO2Et) into C-H bonds of sp3 carbons is the focus of my work. The catalyst for this reaction is a trimeric Ag(I) complex with a cis-bidentate monoanionic nitrogen ligand, 2-pyridylpyrrolide. My research is the development of new homogeneous catalysts for alkane functionalization by this catalyst system.

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Scope and limitation

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Selectivity

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Mechanistic Investigation of Alkane Functionalization

Our catalyst also inserts the carbene fragment into the C/C bond of benzene to give a cycloheptatriene, which is regarded as extremely surprising in terms of breaking such a strong, resonance-stabilized C/C bond, that in the arene. DFT calculations show that this reaction is thermodynamically favored, but less so than carbene insertion into the arene C-H bond; thus, the catalyst accomplishes non-thermodynamic selectivity; here, mechanism is more important than thermodynamics.

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My results may provide a new molecular alkane functionalization method that is environmentally cleaner, economically superior and allows the large reserves of untapped remotely located natural gas to be better used as primary feed stocks for fuels and chemicals.

Lab Member

Kuntal Pal

Biography

Kuntal Pal was born in Howrah, India in 1978. He got his early chemistry education of Bachelor and Master’s Degrees from the University of Calcutta. Soon after, he joined as a NET-CSIR junior research fellow at IIT Kanpur, India to pursue a Ph.D. under the supervision of Professor Sabyasachi Sarkar in the field of bioinorganic chemistry. He was inspired by the biomimicing model studies of a Mo-containing enzyme and worked on the project of synthesis and reactivity studies of model complexes in relevance to the native enzymes of sulfite oxidase and nitrate reductase. Kuntal synthesized several metal complexes of dithiolene ligands which are structurally very similar to the active site of enzyme. He learned x-ray crystallography to analyze the structure of the synthesized complex. For functionality, his synthesized model complexes were subjected to reactivity studies with native substrate followed by comparisons of their kinetics with that of the native enzyme. Kuntal performed DFT computational work on the synthesized metal complexes to understand the chemistry involved and the mechanistic aspects of the enzymatic reaction. He was awarded the Ph.D. degree in May, 2008.At the end of Kuntal’s dissertation work, he was very much interested in the activation of small molecules which are toxic in nature (carbon monoxide, nitric oxide) using model complexes associated with metal-organic framework. To enhance his research skill at the international level, he moved to Japan as a Japan Society for the Promotion of Science (JSPS) post-doctoral fellow in Osaka University under the guidance of Professor Kazushi Mashima. Kuntal developed a series of bimetallic Mo/Cu containing tri and tetranuclear clusters systems as precursor catalysts for the activation and removal of toxicity of carbon monoxide.After completing the JSPS program, Kuntal joined on a joint collaboration project under Professor Caulton and Professor Baik in the Department of Chemistry at Indiana University. Kuntal’s current research is focused on electronic structure calculations and the finding of true mechanistic pathway on newly developed variety of catalytic reactions here at Indiana. Currently, he is working on the mechanistic studies of the transition metal (Cu(I) & Ag(I)) catalyzed C-H bond activation of alkanes on a pyridylpyrrolide-based ligand platform. Together with another Caulton group postdoc, Atanu Das, he is working on redox-active ligands having impact on interaction of metal centers with O2.


Research Projects

For this project, Kuntal is doing DFT calculations to understand the mechanism of a catalytic alkane C-H bond functionalization.  Initial experimental observations here at Indiana by Jaime Flores found the species [LAg] as an active catalyst, from a trimeric precursor.  [LAg] can interact with HC(CO2Et)(N2) to form two possible intermediates; N2 bound diazoalkane and N2-free carbene; both are thermodynamically equally accessible.  Kuntal is now on the way to finding out how the C-H bond of an alkane can be cleaved.  Does this reaction proceed via an even-electron or a radical mechanism?

DFT Studies on the Mechanistic Aspects of Alkane C-H Activation by Coinage metal-carbene complexes (M = Cu, Ag)

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Graduate Student

Atanu Kumar Das

Biography

Atanu Kumar Das was born in 1982 in West Bengal, India. He completed his Bachelor of Science (BSc) major in chemistry and minor in physics and mathematics, at Ramakrishna Mission Residential College, Narendrapur affiliated under Calcutta University in 2003. In 2005, he received his Master of Science (MSc) in chemistry (specialization in Inorganic chemistry) working on “Synthesis of 21-thiacalix(4)phyrin with two meso sp3 carbons” from Indian Institute of Technology, Bombay, India. He completed his Ph.D. in 2009 under the supervision of Professor Wolfgang Kaim, Institute for Inorganic Chemistry, University of Stuttgart, Germany. His doctoral thesis focused on “Structural, electron transfer and spectroscopic studies of transition metal complexes with redox-active ligands”. Atanu spent one year (2009–2010) as a postdoctoral fellow with Assistant Professor Hong Soon Hyeok at Nanyang Technological University, Singapore working on “Gold-abnormal carbene catalyzed organic transformation”. Atanu joined Professor Kenneth G. Caulton’s group in July 2010 pursuing his second postdoctoral research.


Research Projects

Redox-active Ligand Mediated Bond Making/Breaking Transformations

Metal complexes with redox-active ligands have gained much attention not only for their unique and interesting electron transfer behavior but also the prospective role in either stoichiometric or catalytic molecular transformation. Redox-active ligands have more energetically accessible levels that allow redox reactions to change their charge state. Pyridylpyrrolide ligands (scheme 1) have seen considerable recent research from the synthetic perspective, they have not been considered as redox active. We are exploring the 2-pyridylpyrrolide, (Ln)class of ligands as possible redox active and to expand the redox activity of their metal complexes beyond simple-metal-centered redox chemistry.

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Reactivities of [(L0)Ir(Cp*)](BArF4)

A. Activation of oxygen: Electron Buffering from Ligand

The coordination and activation of dioxygen by transition metal complexes continues to be the focus of considerable interest in attempts to develop new, atom economical oxidation catalysts. However activation by a d6metal [Ir(III) or Ru(II)] complex isn’t well explored so far. A redox non-innocent ligand 2.2’-pyridylpyrrolide that has the potential to store the redox equivalent, both in oxidative and reductive direction, was installed to synthesize a mononuclear [(L0)IrIII(Cp*)Cl] (L0= 2.2’-pyridylpyrrolide) complex to test the reactivity with O2. I find the 18ecomplex [(L0)IrIII(Cp*)Cl] is inert to O2, indicating outer sphere electron transfer isn’t viable and O2isn’t strong enough to replace the chloride. However, the unsaturated 16especies [(L0)IrIII(Cp*)]+obtained from reaction of [(L0)IrIII(Cp*)Cl] with NaBArF4, reacts with O2in the time of mixing (Scheme 2) to form a [(L0)IrIII(Cp*)(O2)]+adduct. The remarkable fact is that the process is irreversible and redox change for the adduct formation occurs at the pyridylpyrrolide. To the best of our knowledge, this is the first example where d6Ir(III)-complex acts as a reducing agent to activate O2. DFT calculations (fig. 1) were conducted by Dr. Kuntal Pal to rationalize the electronic structure of [(L0)IrIII(Cp*)(O2)]+. Different trapping experiments help me to understand the answer to the question, “How many oxygen atom(s) can effectively be transferred to oxidize the substrate?”

Schematic representation of O2activation by pyridylpyrrolide-Ir(III) and oxidation of substrate

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B. Heterolytic Cleavage of H2

I am interested in extending the redox participation of the pyridylpyrrolide ligand to other redox reagents, a significant one being H2. Questions of interest here are whether H2is a strong enough oxidant to oxidize iridium(III), and what the product of this reaction will be 2H+or dihydride, coordinated dihydrogen, or heterolytic splitting of H2to Hand H+. I find that reaction of dihydrogen (1 atm) with Cp*L0Ir+in CH2Cl2is complete in time of mixing at RT, with rapid color change from green to orange. The iridium containing product is exclusively (Cp*Ir)2(m-H)3+, identified by spectroscopic comparison to an authentic sample. Also produced stoichiometrically (one mole per one Ir) is HL0, the neutral ligand where an H2-derived proton is on the pyrrole nitrogen. Finally, one proton is produced for every two-reagent complexes (eq. 1). This reaction is thus iridium-promotedheterolyticsplitting of three moles of H2. We are using DFT calculation to understand the reaction mechanism.

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C. Electrocatalytic CO2Reduction

CO2is the planet’s most important source of carbon and one of the most important atmospheric gases contributing to the greenhouse effect. These are the reasons that its electrochemical reduction into fuels attracts sustained attention. Being motivated by our newly discovered“redox-storage”property of pyridylpyrrolide ligand which serve as“electron-buffer”in small molecule activation e.g., hydrogen oxidation, oxygen activation, we are interested in exploring further the reductive reactivity of M(pyridylpyrrolide)2type of complex.

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Fe(L2)2(THF) (fig. 2) was synthesized and employed to reduce CO2electrochemically. I have established that Fe(L2)2shows catalytic current flow at -2.42 V (vs. Ag/AgCl) (fig 3) when CV is

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run under 1 atm CO2. Analysis of the colorless precipitate formed concurrently in the electrochemical cell indicates the co-product to be [N(n-bu)4]CO3, hence the product of capture of O2-by CO2in eq 2; [N(n-bu)4]+is the cation in my supporting electrolyte. My current and future plans are to search the liquid phase for other CO2reduction products, particularly more reduced (e.g., alkoxides) and C2species.

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