Major Recognitions and Honors
Schulich Visiting Professor Lectureship, Haifa, Israel, 2011
Sita, L. R. “E Unum Pluribus (‘Out of One, Many’): New Paradigms for Expanding the Range of Polyolefins through Reversible Group Transfers,” Angew. Chem. Int. Ed. 2009, 48, 2464.
Wei, J.; Zhang, W.; Wickham, R.; Sita, L. R. “Programmable Modulation of Co-monomer Relative Reactivities for Living Coordination Polymerization through Reversible Chain Transfer between “Tight” and “Loose” Ion Pairs,” Angew. Chem. Int. Ed. 2010, 49, 9140.
Yonke, B. L.; Reeds, J. P.; Zavalij, P. Y.; Sita, L. R. “Catalytic Degenerate and Nondegenerate Oxygen Atom Transfers Employing N20 and CO2 and a M(II)/M(IV) Cycle Mediated by Group 6 M(IV) Terminal Oxo Complexes,” Angew. Chem. Int. Ed. 2011, 50, 12342.
Carbon-Monoxide-Induced N-N Bond Cleavage of Nitrous Oxide That Is Competitive with Oxygen Atom Transfer to Carbon Monoxide as Mediated by a Mo(II)/Mo(IV) Catalytic Cycle,” J. Am. Chem. Soc. 2011, 133, 18602.
Crawford, K. E.; Sita, L. R. “Stereoengineering of Poly(1,3-methylenecyclohexane) via Two-State Living Coordination Polymerization of 1,6-Heptadiene,” J. Am. Chem. Soc. 2013, 135, 8778.
Wei, J.; Hwang, W.; Zhang, W.; Sita, L. R. “Dinuclear Bis-Propagators for the Stereoselective Living Coordinative Chain Transfer Polymerization of Propene,” J. Am. Chem. Soc. 2013,135, 2132.
Keane, A. J.; Zavalij, P. Y.; Sita, L. R. “N-N Bond Cleavage of Mid-Valent Ta(IV) Hydrazido and Hydrazidium Complexes Relevant to the Schrock Cycle for Dinitrogen Fixation,” J. Am. Chem. Soc. 2013, 135, 9580.
Living Coordination Polymerization of Alkenes
At over 140 million tons per year, and with a projected growth rate of 5 – 7% per year for the foreseeable future, humanity is wholly dependent upon polyolefin-based materials prepared through the coordination polymerization and co-polymerization of ethene, propene, and higher 1-alkenes. Of particular importance for the future then is the development of new catalysts and polymerization processes that can continue to significantly expand the range of polyolefins and their end-use applications. With respect to this, our research program is currently focused on the development of homogeneous (soluble) transition-metal-based catalysts for the (stereoselective) coordination polymerization of ethene, propene, and 1-alkenes. In addition, we are pursuing, within a living polymerization system, the development of ‘one catalyst, many materials’ strategies that involve the initial identification of dynamic fast and reversible bimolecular processes that are competitive with pseudo first-order chain-growth propagation. The goal is then to establish mechanistic control points that can provide external control over the relative rates of these processes in such a fashion that a near continuum of different polyolefin grades between two different limiting stereochemical microstructures, co-polymer compositions or polymer architectures can be generated with a high degree of precision from a single catalyst. Concurrent with our catalyst development and mechanistic investigations have been those focused on probing the material science and engineering applications of these new classes of precision polyolefins. Our goals are to
correlate strategic synthetic designs with bulk macro- and microphase morphological structures in the solid-state for the development of new classes of thermoplastic elastomers and for novel photonic applications of pure polyolefin materials that can be produced on a commodity scale. In addition to the synthesis of organometallic compounds employing glove-box and Schlenk-line techniques, our research efforts utilize a wide-range of instrumental and spectroscopic techniques, including, high-field (600 MHz) 2D NMR, atomic force microscopy (AFM), transmission electron microscopy (TEM), single-crystal and powder X-ray diffraction (XRD), small angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA), and 1D and 2D gel permeation chromatography (GPC), name just a few.