Lawrence R. Sita - US grants

This award in the Inorganic, Bioinorganic and Organometallic Chemistry Program supports Lawrence Sita, University of Maryland College Park, for work on amidinate-based olefin polymerization catalysts. Compounds such as cyclopentadienyl dimethyl zirconium acetamidinate are activated with borate cocatalysts to provide an active species that promotes the stereospecific living Ziegler-Natta polymerization of olefins and the living cyclopolymerization of non-conjugated dienes. New catalysts will be designed, synthesized and evaluated. Kinetic analyses will probe the detailed mechanism, including identification of factors that control the stereochemistry of the growing polymer chain.

Polyolefins are a large class of commercial plastics that includes polyethylene and polypropylene. Block copolymers often show desirable properties such as elasticity, crystallinity, thermoplasticity and solubility. These new specialty plastics are used in the packaging, electronics and textile industries. Metallocene and amidinate catalysts provide routes into new and useful polyolefins.

With this award from the Major Research Instrumentation (MRI) Program, the Department of Chemistry at the University of Maryland in College Park will acquire an X-ray photoelectron spectrometer. This equipment will enhance research in a number of areas: a) nanostructure reactivity and registration at solid surfaces; b) derivatization of metal and metal oxide surfaces via molecular and mesoscopic self assembly; c) chemical vapor deposition of metal oxides; d) combinatorial synthesis of functional oxides; and e) soft chemical routes to novel solid state materials.

The X-ray photoelectron spectrometer (XPS) is used for chemical analysis. It irradiates a sample with a beam of monochromatic X-rays and the energies of the resulting photoelectrons are measured and related to specific elements. XPS often plays a crucial role in defining the system under study. The work to be carried out by these investigators represents a highly coherent attack on a range of issues at the forefront of materials chemistry.

This Nanoscale Interdisciplinary Research Team (NIRT) will focus on the effects of the discreteness of atomic structure and charge on the electronic properties of nanoscale devices. New tools will be developed to examine the structure and structure fluctuations of nanoscale devices while simultaneously measuring electronic transport properties. Specifically, nanoscale metal wires will be fabricated in situ in an ultra-high vacuum combined scanning-tunneling microscope/atomic-force microscope. The atomic-scale structural fluctuations of these wires will be studied during electromigration while simultaneously acquiring electronic transport information. Small gap junctions will be also be fabricated, and used to study simultaneously the atomic structure and electronic transport properties of carbon nanotubes and novel molecular devices. Concurrently, the sensitivity of nanoscale devices to fluctuating electrostatic environments will also be studied. New charge sensors such as carbon nanotube-based single-electron-transistors and semiconducting carbon nanotube field-effect transistors will be investigated. Efforts to manipulate the charge sensitivity of these devices through chemical modification will be explored. Undergraduate and graduate students will be involved in the development and use of cutting-edge research tools and will receive excellent training in interdisciplinary research at the frontiers of nanotechnology.
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This Nanoscale Interdisciplinary Research Team (NIRT) is attacking two fundamental and intertwined problems, which will increase in importance, as electronic device dimensions become smaller. First, the discreteness of atomic matter becomes significant in determining structural stability of devices. Will fundamental properties such as the bonds between molecules remain stable during device operation. Second, the discreteness of charge causes significant sensitivity of the device to fluctuations in the electrostatic environment. How will local electric fields or static charge affect the devices. The quantum nature of electronic transport in nanoscale systems requires that the structure of molecular-scale devices - as well as their interconnects - be controlled at the atomic level. Techniques will be developed to simultaneously image the atomic structure of molecules, nanotubes, nanoscale wires, and interconnects while measuring electronic transport properties. Changes in the local electrostatic environment at the level of motion of single charges will have pronounced effects on the electronic transport through nanodevices. The proposed research will focus on the charge sensitivity of nanostructures ranging from superconducting single-electron transistors coupled to nanowires to semiconducting carbon nanotubes. Undergraduate and graduate students will be involved in the development and use of cutting-edge research tools and will receive excellent training in interdisciplinary research at the frontiers of nanotechnology.

With support from the Major Research Instrumentation (MRI) Acquisition Program, the Department of Chemistry and Biochemistry at the University of Maryland College Park (UMD) will acquire a 600 MHz spectrometer. The spectrometer will improve the diverse research capabilities at UMD in chemistry, biochemistry and materials science, as well as enhance research at Howard University and the Catholic University of America. Research that will be impacted include the design of catalysts for Ziegler-Natta polymerization, basic understanding of protein folding, synthesis of nanoparticles for use in hydrogen fuel cells, and the design of synthetic ion channels.

Nuclear Magnetic Resonance (NMR) spectroscopy is the most broadly used tool available to chemists for the elucidation of the structure of molecules. It is used to identify unknown substances and to provide information on the arrangement and connectivity of atoms in molecules. This award will provide these essential analytical capabilities to chemists, biochemists, and chemical engineers at the three institutions sharing the use of the nmr facility at UMD. To maximize the training component of the award, a course in practical nmr spectroscopy for senior and first-year graduate students will be established. The course will be co-taught by participating faculty from the three institutions.

This award in the Inorganic, Bioinorganic and Organometallic Chemistry program supports research by Professor Lawrence B. Sita at the Univesity of Maryland at College Park to use a monocyclopentadienyl, amidinate ligand combination to impart significant kinetic stability to a variety of early transition metal alkyl complexes bearing beta-hydrogens. The primary objectives are to utilize neutral and cationic group 4 and 5 monocyclopentadienyl, monoamidinate metal alkyl complexes as a means to investigate mechanistic aspects of Ziegler-Natta polymerization and the highly selective trimerization of ethylene and alpha-olefins. This work seeks to determine how intra- and intermolecular dynamic processes can be harnessed to expand the structural and microstructural range of polyolefin materials that can be prepared through the Ziegler-Natta process. The work will test and validate a new paradigm for accessing a wide range of polyolefin microstructures through two-state bimolecular control that is based on degenerative-transfer living Ziegler-Natta polymerization. For the selective oligomerization of alpha-olefins, the proposed studies will contribute to an understanding of the factors that can serve to achieve both higher activities and selectivities in a new generation of catalysts.

The broader impact of this work is the potential development of more efficient catalysts and new polyolefin materials that will be beneficial to both the world economy and society. The proposed work will provide an important vehicle by which future generations of undergraduates, graduate students, and postdoctoral researchers can be trained with the promotion of diversity in mind.

With this award from the Chemical Catalysis Program, Professor Lawrence R. Sita from University of Maryland at College Park will work on discovering and developing new paradigms, catalysts and polymerization processes that can be used to significantly expand the range of polyolefins and their end-use applications in support of new technologies. The primary hypothesis that will be pursued is that different categories of fast and reversible dynamic processes that are competitive with chain-growth propagation can be introduced to establish two-state living coordination olefin polymerization in which the relative rates of the dynamic process and propagation can be brought under external control to direct polyolefin production over a spectrum that is delineated by two extreme boundary structures. Several new paradigms will be conceived and developed in order to remove existing restrictions that are presently imposed by classical approaches that are based on a one-to-one correlation between catalyst structure and polyolefin product.

In addition to the scientific impact this work will provide support for a continued scientific and economic competitive position of the U.S. in the global polyolefin and chemical industries and support training of future generation of scientists and engineers for science, technology, engineering, and mathematics (STEM) related careers. Importantly, the discovery and development of new technological inventions and innovations of commercial value will support the national economy.

With this award, the Chemical Catalysis Program in the Chemistry Division is funding Dr. Lawrence Sita from the University of Maryland to develop transition-metal catalysts that can be used for the production of high-value specialty chemicals from readily available, safe, and inexpensive starting materials, such as nitrogen, carbon dioxide, carbon monoxide, and sulfur.

Advances in chemical technologies for the commercial production of high-value, industrial chemicals must be made in the near term in order to meet the increasing burdens placed on natural resources, energy, and the environment as the global population is anticipated to expand by 3 to 4 billion people over the next 50 years. In response to these needs, the primary objective of the project is the development of transition-metal catalysts that can be used to produce value-added, specialty chemicals from readily-available, inexpensive and safe starting materials, such as nitrogen, carbon dioxide, carbon monoxide, nitrous oxide and sulfur. The broader impact of this work is the potential development of more atom-economical and energy-efficient, industrial-scale chemical transformations that will be beneficial to the world economy, the environment, and the society and that can reduce the health- and security-risk of current technologies that require the generation, transportation, and on-site storage of hazardous reagents and intermediates. The proposed work will further provide an important vehicle by which future generations of undergraduates, graduate students, and postdoctoral researchers are trained.

The focus of the research is the synthesis and characterization of mid-valent, second- and third-row, group 5 (Nb, Ta) and 6 (Mo, W) metal complexes with cyclopentadienyl amidinate (CPAM) and cyclopentadienyl guanidinate (CPGU) ligands. These complexes are suited for the study of the coordination and "fixation" of small molecules possessing X-Y multiple bonds (e.g., N2, O2, N2O, CO and CO2). The interaction between these metal complexes and the small molecules leads to (1) X-Y multiple bond cleavage compensated by the formation of strong M-X and M-Y bonding interactions, and (2) pathways for atom-economical, X- and Y-transfers to a substrate, which complete the catalytic cycle with respect to the starting metal complex. The CPAM and CPGU, molecularly-discrete complexes will be fully characterized both in solution using NMR, EPR, UV, and IR spectroscopies, electrospray mass spectrometry, and electrochemistry, and in the solid state using single-crystal X-ray analysis, elemental analyses, and IR and EPR spectroscopies.

With this award from the Major Research Instrumentation (MRI) and Chemistry Research Infrastructure and Facilities programs, Professor YuHuang Wang from the University of Maryland College Park and colleagues Janice Reutt-Robey, Lawrence Sita, Chunsheng Wang and Liangbing Hu have acquired an atomic force microscope system. In an AFM a laser beam is directed to a surface by means of a cantilever and tip. As the cantilever is displaced by interacting with the surface, a reflection of the laser beam is displayed on a detector (photodiode). In this way an image of the surface can be created with the aid of an electronic system. In general, an AFM has three major abilities: force measurement, imaging, and manipulation. The microscope is an important tool in the investigation of the surfaces of materials. It is used in fundamental and applied research to study morphology of surfaces, surface imaging and functionalization, electrical, magnetic, chemical and mechanical properties of surfaces. This knowledge enables advances in developing better materials in fields such as nanoscience and energy science. The instrument is used in the research and training of undergraduate and graduate students preparing them for technical careers and opportunities for advanced education.

The proposal is aimed at enhancing research and education at all levels, especially in: (a) studying nanoparticle transport and internalization at model interfaces, (b) probing quantum defects in low-dimensional carbon materials, (c) mapping peak current and peak force of carbon nanoparticles in covetics, (d) imaging small circuits on glass, (e) studying living polymerization and direct assembly of precision polyolefins, (f) assessing the integrity and stability of xeolite membranes, (g) understanding and tailoring designing of solid state interphases for nanostructured silicon electrodes and (h) studying solid electrode interface formation, structure and evolution of molybdenum disulfide.

Electrocatalytic Metal-Mediated Nitrogen Fixation
As the world's population is expected to increase from 7 billion to nearly 10 billion people within the next 35 years, there is the need to develop and commercialize new energy-efficient and environmentally-benign industrial processes that can provide chemicals that are required to support and advance civilization. In this regard, the century-old Haber-Bosch (HB) process, which converts nitrogen (N2) and hydrogen (H2) into over 140 million metric tons of ammonia (NH3) to be used as fertilizer each year, is critical for our survival, however, as practiced, it currently consumes up to 5% of the world's energy production and a substantial amount of chemical waste is generated to provide the required amount of hydrogen. More importantly, at the molecular level, scientists do not know how 'nitrogen fixation' by the HB process works. In this project, Dr. Sita and his research group are pursuing a new design for the development of chemistry that uses electricity as the source of power and water (H20) rather than hydrogen for achieving the ultimate goal of inexpensive, energy- and chemically-efficient nitrogen fixation that will not have an enormous future impact on natural resources and the environment.

With funding from the Chemical Catalysis Program of the Chemistry Division, Dr. Sita of the University of Maryland is seeking to develop an electrochemically-driven catalytic process for the energy efficient and atom-economical conversion of N2 into NH3. Research activities include the design and optimization of molecularly-discrete mononuclear and dinuclear molybdenum (Mo) complexes that can coordinate N2 in a manner that leads to low temperature N-N bond cleavage, N-atom functionalization, and release of a nitrogen-containing product in a fashion that recycles the Mo complex back to the initial starting state. Bulk electrolysis, using optimized metal electrodes and trialkylsilyl halides, is being employed to establish a chemical process that is catalytic in the amount of Mo complex that is required for the production of trialkylsilylated amines from N2. Acid hydrolysis of the trialkylsilylated amines is providing NH3 and enabling recycling the trialkylsilyl halide. Validation of the new proposed paradigm for achieving electrocatalytic nitrogen fixation is providing an important scientific foundation that can contribute to the further advancement of chemical technologies that are beneficial to global civilization and the world economy. This project is also training a diverse new generation of scientists in interdisciplinary areas of electrochemistry, inorganic and industrial chemistry, catalysis, and reaction mechanisms. Dr. Sita is engaging in outreach activities with the general public to promote a better understanding of chemistry and its critical role in supporting civilization and a better quality of life. In particular, Dr. Sita is providing STEM education at the K-12 level and especially through involvement with groups of students from underrepresented groups.

This award is supported by the Major Research Instrumentation (MRI) and the Chemistry Research Instrumentation and Facilities (CRIF) Programs. Professor Lyle Isaacs from University of Maryland College Park and colleagues Lawrence Sita, Chunsheng Wang, Dongxia Liu and Efrain Rodriguez are acquiring a 500 MHz solid-state nuclear magnetic resonance (NMR) spectrometer. An NMR spectometer measures the magnetic properties of atoms when molecules are exposed to various frequencies of light. These signals identify the atoms present in the compound. This spectrometer probes the properties of solid materials, including batteries, polymers, catalysts and biomolecules. The NMR is used by chemists, engineers and their students working on interdisciplinary research in materials, nanoscience, catalysis and energy science. The instrument is the first solid-state NMR at the University of Maryland. It is a resource available to other institutions in the region and a valuable instrument to train students in NMR techniques preparing them for their later careers in academia or industry.

This NMR spectrometer enhances research and education at all levels. The infrastructure acquisition impacts the preparation of cucurbit[n]urils, studies of intermetalloid clusters, and the self-assembly of ionophores and hydrogels. The instrumentation is also used to study catalytic metal-mediated small molecule fixation and to carry out carbon-hydrogen bond activation with oxygen as direct oxidant. The spectrometer is useful for preparing new catalysts from zeolite materials, for probing structures in superconducting solids and for studying electrochemical energy storage.