Biography
I am a visiting scholar from Germany, staying here in Bloomington from July till end of October. I was born in Frankfurt (Germany) and studied chemistry at the Georg-August-University in Göttingen. I obtained my M.Sc. in the group of Prof. Sven Schneider, working on the reactivity of Co-PNP-pincer-complexes. I subsequently started to pursue my PhD as a graduate student in the Schneider group.
My graduate research focuses on N2-splitting and functionalization utilizing functional pincer ligands. In this project I want to transform N2, which is a very unreactive molecule, into other N-containing molecules like ammonia or other organic molecules.
Research Projects
Nitrogen is beside carbon, oxygen and hydrogen one of the main elements found in organic molecules. Even though nitrogen makes with 80% the major part of our atmosphere most of these organic molecules are not made directly from N2 but from its reduced form, ammonia, which is also essential for agricultural industry since most fertilizers contain at least one nitrogen atom. On industrial scale this transformation of N2 into NH3 is done via the so-called Haber-Bosch-process in gigantic scales with over 100 million tons per year, which also shows its high importance.
Since the reaction conditions of this process are very harsh (150-350 bar at 400 – 500 °C) there are enormous efforts in designing biomimetic catalysts for this reaction. Many recent studies of such homogeneous systems have shown that metal-nitrides seem to be a key intermediate in the catalytic cycle. Since the mechanism of N2-splitting is nearly completely unknown, there’s a high interest in synthesizing complexes which form bonds with N2 and then look on the conditions that are needed to initiate N2-splitting. In this way the mechanism of N2-splitting as well as the requirements regarding the supporting ligand can be investigated, which helps designing more effective catalysts for the transformation of N2 into NH3.
Within a close collaboration the Schneider (U Göttingen, Germany) and Caulton groups study N2-splitting mediated by dinuclear-PNP-complexes, as recently reported for [{(PNP)ClMo}2{µ-N2}] (1)[1]. Splitting of the N2-bond in such complexes leads to the formation of metal-nitrides, which can be either used as a catalyst for ammonia formation or to form new C-N-bonds. In an ideal case such C-N-coupling reactions would open up the possibility to generate N-containing organic molecules directly from N2 without the use of ammonia, which would make their synthesis much more efficient and economic.
[1] G. Silantyev, M. Förster, B. Schluschaß, J. Abbenseth, C. Würtele, C. Volkmann, M.C. Holthausen, S. Schneider Angew. Chem. Int. Ed. 2017, 56, 5872-5876.
Biography
I grew up in Seoul, Korea and moved to Richmond, Virginia when I was fifteen. I graduated with a BS in chemistry from Randolph Macon College. While at RMC, I was given opportunities to have three years of undergraduate research experience in Serge Schreiner’s organometallics research group including two summers of research. My undergraduate research focused on small molecules activation by the PNP pincer ligated transition metal complexes (groups 9 and 10 metals!) and CO2 reduction with the activated complexes. Outside of chemistry, I love doing music: listening, playing (I’ve played violin and piano since I was six). Other than that I like taking a nap and just slacking around a lot.
Research Projects
In my C500 project, reactivity of two low valent chromium (Cr(II) and Cr(III)) compounds stabilized by bis(pyrazolyl)pyridine (BPZP) towards nitrate activation will be explored with the goal of contributing to design of metal complexes that are capable of proton coupled electron transfer (PCET) to accomplish reductive deoxygenation of the oxoanions such as NO2– and NO3–.
NO3– + 2H+ + 2e– → NO2– + H2O
NO2– + 2H+ + 2e– → NO– + H2O
The redox active ligand, BPZP, used in this study is with R groups being proton (H2L) which may play a key role for the nitrate reduction. For instance, protons are bonded to N of the pyridine ring outwardly, thus, once NO3– is coordinated to the metal center, the prolific proton can possibly interact with the closest O atom of the nitrate by hydrogen bonding followed by N-O bond cleavage (*).
Prior to the activation of NO3–, as the previous studies in the group showed that the metal-ligand chlorides precursors have low solubility, I am currently working towards chloride substitution using TMS-triflate to improve the solubility.
Once compound 2 is prepared and fully characterized, nitrate coordination and reduction will be thoroughly studied. An analogous study with Cr(II) will be carried out.
Biography
Brian Jeffrey Cook was born in Trenton, New Jersey in 1989 and grew up in the neighboring suburb of Lawrenceville, NJ. An interest in chemistry grew out of proficiency in high school and led to Brian double majoring in Biochemistry and Chemistry/ACS Certification track at Seton Hall University (South Orange, NJ campus). While at Seton Hall, Brian received numerous commendations, including the Undergraduate Organic Chemistry Award from the American Chemical Society Divisions of Polymer Chemistry and Polymer and Materials Science, and the New Jersey Institute of Chemists award. At Seton Hall, Brian was involved in numerous research projects, for example, in the Murphy group, the synthesis of new ruthenium-ruthenium and ruthenium-rhenium tetrametallic dendrimers with previously under-utilized bridging ligands for investigating metal-metal communication.
Research Projects
Redox active (“non-innocent”) ligands are becoming increasingly important partners to transition metal centers in assisting with delivering multiple electrons to substrates. One particular instance in which these ligands may provide such assistance would be the idea of “electron storage”, in that the ligand could hold some of the required electrons needed for the reaction, lessening the burden on the metal. If an iron(II) center reacting with an oxidizing substrate only has to reach iron(III) and not iron(IV) or iron(V) this would obviously allow the reaction to be much more energetically favorable, and thus faster. One such redox active ligand has been identified by the Flood group here at Indiana University called 2,6-(bis)-tetrazinylpyridine (btzp). The tetrazine moieties offer unique optical and electronic properties, including an unusually low pi* orbital, giving rise to the overall redox non-innocence of btzp.
While proven to be redox active alone in solution and complexed to a metal in the form of Fe(btzp)2,I am currently working on developing, characterizing, and eventually applying 1:1 metal complexes with btzp in the form of M(btzp). M(btzp) is much more desirable because multiple empty metal orbitals are available for substrate binding, and we would predict high reactivity for these complexes. Currently, the metals under my investigation are Fe, Ru, and Zn. Fe and Zn are attractive choices because they allow exploration of the purely redox active character of the ligand with a redox inert metal (Zn) and the abundance in the earth’s crust of Fe makes it a hot target for catalyst synthesizers. One scheme for developing these complexes is shown below (scheme 1 where M = Zn, Ru). Ru is attractive because of its relative ease of handling and characterization (almost exclusively low-spin and diamagnetic), whilst being an electronic analog to Fe. Besides complete characterization, my plan for these complexes is the reduction of CO2and N2as we continue to discover more and more about the potential and hidden power stored in redox active ligands.
To-date I have synthesized and characterized (btzp)RuCl2(CO), incorporating the CO ligand as a reporter, which shows that btzp is the most electron withdrawing pincer ligand yet discovered, and thus with the highest CO stretching frequency observed.
In addition, I have developed the 3d metal chemistry of the 2,6 bis-pyrazolyl pyridine chemistry of Fe and Co. This ligand is highly proton-responsive and redox active, leading to rich possibilities in small molecule activation. I have established the general tendency of the deprotonated version of these pyrazolates to aggregate, including any available oxo ligands. I have also shown that hydride reagents convert the cobalt complex to an aggregated species of Co(I), in green, to give an unprecedented oxo (in red) complex of this four coordinate
monovalent cobalt. I have a low-valent but highly fragile reduced cobalt species which I am currently characterizing as a possible reagent to reduce N2. I have also shown that LCo(PEt3)2 reacts rapidly with N2O to oxidize all phosphine to liberate OPEt3, and L2Co2(m-OPEt3), the latter containing an unprecedented bridging phosphine oxide. I already have obtained LFe(DMAP)3, where DMAP is para-dimethylamino pyridine, and this reacts rapidly with CO2 to give a carbonate product.
Biography
My hometown is Richmond, Utah in beautiful Cache Valley. I received a B.S. degree in chemistry from Utah State University (2014). While at Utah State, I studied under Dr. John Hubbard (organometallics) and Dr. Yujie Sun (water oxidation catalysts). My interests and hobbies, outside of chemistry, include: backcountry skiing in Utah powder, traditional climbing, golfing and reading. I chose Indiana University because of the outstanding friendliness of the department, the moderate size of research groups, the opportunity to collaborate, and CO2 activation research in the Caulton Group.
Research Projects
A central pillar to my research goals and philosophy is the elucidation of fundamental principles and its meaningful application to 21st century national and global problems. We face a twofold problem: satisfying rising energy demands without increasing anthropogenic climate change and conserving carbon-based resources. To address conservation of carbon-based resources, we choose the challenge of CO2 reduction to value-added, multi-carbon products.
Frontier research in this field proposes, as an attractive alternative to precious metals, redox-active ligands to assist first-row transition metals in participating in 2e– reactions by acting as an electron storage site. My current work is centered on [CrL]2 which features two divalent chromium atoms supported by a potentially redox-active pincer ligand, bis-(pyrazolate)pyridine, L2−. My goal is to exploit the reducing power (both native and when chemically reduced with KC8) and the ligand electrophile-responsiveness (proton and alkali metal) in substrate transformations. Indeed, [CrL]2 when treated with KC8 in a 1:2.3 mole ratio promptly reacts with excess CO2 to yield K10L8Cr8(CO3)4Cl2 + 4 CO which is an aggregate of the [K2Cr2L2(μ-CO3)] building block.
Figure 1. ORTEP drawing of K10L8Cr8(CO3)4Cl2 viewed nearly down the idealized C2 axis (K2-K5 line). All red atoms are CO2 derived oxygen.
Recently, I have extended the built-in reducing power and Brønsted basicity of [CrL]2 to bond scission or bond reduction of N=N double bonds in the substrate. I seek to develop the general principles that govern when [CrL]2 directs two-electrons to one substrate or one-electron to two substrate ligands coupled with the influence of alkali metal on the overall transformation. The reduced substrate will then bind to the newly generated Cr(III) in order to satisfy coordination number demands; this may allow for the capture of “intermediate” products, i.e., before protonation occurs, in either a chromium monomer or dimer. Ultimately, this study can potentially contribute understanding to N-O bond scission in hydroxylamine along the nitrogen cycle as nitrogen oxyanions are converted back to ammonia or dinitrogen.
Biography
I am a native of Springfield, MO where I graduated from Missouri State University with my B.S in Chemistry, 2011, and M.S. in Chemistry, 2013. My undergraduate advisor was Dr. Mark Richter under whom I studied electrogenerated chemiluminescence of Ru-chelate complexes, and I obtained my Master’s degree under the tutelage of Dr. Nikolay Gerasimchuk, with a thesis titled “Synthesis and Characterization of the First Non-Chelating Bis-Cyanoximes and their Metal Complexes.” The approach was to use easily ionizable bifunctional ligands to link together Cu(II) and Ni(II) chelates to form MOF-like structures. A desire to expand my skills as a synthetic inorganic chemist led me to Indiana University to join the Caulton group, working on catalysis with first-row transition metal complexes bearing redox non-innocent pincer ligands.
Research Projects
In the short term, my immediate research goals are the synthesis and characterization of monomeric low-valent first-row transition metal complexes of the redox non-innocent pincer 2,6-bis(6-methyl-1,2,4,5-tetrazine)yl pyridine, abbreviated btzp, specifically those of V and Fe, with, as a long term goal, a subsequent evaluation of catalytic abilities of those complexes. Characterization is done by a variety of experimental methods (direct-injection mass spectrometry, X-ray crystallography, NMR spectroscopy, and others) for structure determination and computational methods for electronic structure and to examine the effect of ligands on btzp’s pi-acidic behavior.
An approach I take to my research is to use DFT and experiment in conjunction with one another to not only explain but to some extent to predict chemical behavior. One reaction of particular interest is that of btzp with anhydrous FeCl2 (Scheme 1), with the DFT-predicted product in color.
This is predicted to be a stable 16-electron compound (likely with a solvent molecule filling the remaining coordination site trans to the pyridyl), NMR spectroscopy tells a different story. The elucidation of this product is a goal of my research in the Caulton lab.
DFT has been used to probe chemical behavior, specifically the competition between btzp and other pi-acidic ligands such as CO for electron density in a reduce metal complex. This was probed by vibrational calculations on my target complex (btzp)Fe(CO)2, shown below.
This was compared to the analogous terpyridyl complex and CO stretching frequencies were shown to be lower for the terpy complex, symptomatic of weaker pi acidity of terpy compared to btzp.
Current and future work is the synthesis and isolation of monomeric (btzp)FeA2, where A is a monoanion, with a goal of isolating three-coordinate (btzp)Fe and a subsequent evaluation of its catalytic behavior.
Biography
Alexander V. Polezhaev was born in Moscow, Russia in 1984. An interest in chemistry appeared in high-school and he began study chemistry in Moscow city high-school №171 chemical lyceum. Prior to his graduate career, Alexander was an active undergraduate researcher at Moscow State University with Acad. Nikolay S. Zefirov working on melatonin derivatization for biological activities investigations. He received his specialist degree in organic chemistry in 2006 and then joined prof. A.A Koridze research group in A.N. Nesmeyanov Institute of Organoelement Chemistry. His Ph.D. research involves synthetic organometallic and coordination chemistries and catalysis, including the exploration of small molecule coordination and activation with arene and ferrocene-based pincer complexes and alkane dehydrogenation. During this work, two absolutely new types of complexes were found: metallocenium ions which could be considered as models of intermediates in electrophilic substitution in ferrocene core and cationic metallocenylidene ruthenium pincer complex – analogs of alpha-ferrocenylcarbocations. Additionally, he has teaching experience in Moscow city high-school №171 chemical lyceum and A.N. Kolmogorov high-school supervising talented pupils on his first steps in science. Alexander received his Ph.D. in 2011 and then got a researcher position in N.E. Bauman Moscow State Technical University. He worked as independent researcher in polymer composite material chemistry developing self-healing materials for application in constructions and antibacterial polymers for medicine; two patents resulted from this work.He is interested in various branches of organometallic and polymer chemistry: platinum metal complexes, small molecules activation, metallocene derivatization, homogenous catalysis, non-innocent ligands, self-healing polymers, antibacterial polymers and also in bioorganometallic chemistry.
Research Projects
Alexander Polezhaev’s research goal is to develop new active species that combine two functionalities, unsaturated carbon atom (carbene) and unsaturated metal center, in one molecule. This approach includes simultaneous formation of both functionalities by elimination of a proton from imidazolium fragment and a counterion from the metal center. To realize this in practice, our ligands must fix the metal in β-position to the carbene and prevent rearrangement and formation of a direct metal-carbene bond (Scheme 1).
Scheme 1. Unusual metal-supported free carbene.
Those species contains highly active nucleophilic and electrophilic centers in one molecule; such bifunctional character makes them attractive in numerous processes. We target small molecules such as carbon dioxide, dinitrogen, dihydrogen and nitrous oxide to incorporate them in catalytic processes leading to valuable chemicals. Our approach combines classic transition metal assisted activation of small molecules (Scheme 2) with carbene-derived organocatalysis. Those species can also be considered as intramolecular Frustrated Lewis Pairs and we expect reactivity related to that known for such systems.
Scheme 2. Bifunctional activation of small-molecules with metal and carbene
We also anticipate non-innocent behavior from our ligands in the activation process, such as possible electron-shuttling from substrate to metal and back. We also expect that this ligand class direct could stabilize unusual transition metal oxidation states.
Biography
I was born in Minneapolis, Minnesota in 1995 and grew up in Ann Arbor, MI and Fishers, IN. Currently I am pursuing a B.S. degree in chemistry, with a minor in informatics and physics. I chose to attend Indiana University because of the beautiful campus and its many opportunities, especially for undergraduate research! Outside of chemistry, I enjoy lifting weights, basketball, cooking, and playing Super Smash Bros. Melee. I wanted to work in the Caulton Group to expand my foundation in chemistry and to have the opportunity to apply skills learned in the classroom.
Biography
Immanuel Reim is a visiting scholar from Stuttgart, Germany. He was given the opportunity from the chemistry department of Indiana University Bloomington to join any research group for the upcoming year. Within this program he choose to work in Caulton’s Lab. The program encourages not only the scientific exchange but also cultural exchange to show the differences and similarities between Stuttgart/Germany and Bloomington/USA.
He grew up in Backnang, Germany and finished school at the Max-Born-Gymnasium Backnang in 2011 where he received the GdCH-award. He started his chemical education at the University of Stuttgart in 2011. During his second year he worked as a research assistant at the Fraunhofer Institute IPA in Stuttgart to investigate the dependence of the hardening process of polymers on the initiator concentration. He graduated in 2014 working for Dr. Dietrich Gudat. In the following summer, he joined Dr. Francesca Kerton’s group at the Memorial University of Newfoundland, St. John’s Canada, working on the catalytic ring-opening polymerization of epoxides due to the exchange program RISE organized by the DAAD (German academic exchange service). Currently, he is studying towards his Master degree at the University of Stuttgart.
Research Projects
Immanuel Reim’s research goal is to investigate and characterize the recently found formally zero-valent CoNNCo-complex by Brian Cook towards its reactivity and its usage as reducing agent as each Co can function as a one or two electron reductant.
Therefore, different oxidants will be used to utilize its property. Below, several oxidants are shown which can work as two electron acceptor.
The redox potential of btzpEt 4 is investigated by my coworker Nicholas Maciulis. Therefore, both projects will benefit from gained results of this reaction.
The reagent 2 can either replace the N2 in the original complex 1 and oxidize each Co from 0 to +1 to gain compound 2a or oxidize Co by 2 and form a coordinative single complex 2b or a coordinative polymer 2c. It has to be mentioned that the stoichiometry for product 2a is 1:1 (complex 1: duroquinone) whereas for the product 2b and 2c a stoichiometry of 1:2 is necessary. In comparison reagent 3 will oxidize Co by 2 but can form either a side-on adduct 3a or a terminal 3b product by breaking the NN double bond.
Using Dinitrogen monoxide as an oxidant could lead to the terminal Co-oxo complex 5a which would be interesting since it would challenge theory of the “Oxo-Wall”. But according to theory, the product 5b with two bridging oxygens is more likely.
To test its ability further, the reaction of complex 1 with dipyridyltetrazine (bptz) 6 will be investigated since bptz can be reduced by either 2 or 4 electrons which results in a monovalent 6a or divalent 6b Co. The reduction of bptz can be seen in the change of the 1H NMR chemical shifts. Note, that the divalent Co complex is a diradical species.
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.
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!
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?
In favorable cases, the results of my calculations challenge the experimentalists to do new hypothesis-testing studies, often at low temperature.
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.
Scope and limitation
Selectivity
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.
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.
