Synthesis, Bonding and Properties of Conjugated Transition- Metal Complexes and Polymers

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Professor Hopkins, of the University of Pittsburgh, will synthesize transition-metal compounds having conjugated bonding systems with support from the Inorganic, Bioinorganic, and Organometallic Chemistry Program. These compounds will incorporate an array of bonds to achieve this objective, including metal-metal delta bonds, metal-ligand pi bonds, and ligand pi bonds. In most of the compounds the metal centers will be molybdenum and tungsten, and the ligands will include phosphines, alkylidenes, alkylidynes, and bridging dienes. The compounds to be synthesized will include both monomeric species as well as polymers. Assessments of the effects of conjugation will be made by low-temperature electronic spectroscopy, NMR spectroscopy, X-ray diffraction, and resonance Raman spectroscopy. A number of the compounds will be investigated for their nonlinear optical properties. The research will generate an extensive comparison of the effects of conjugation in inorganic and their classic organic analogues. %%% A fundamental concept in organic chemistry is conjugation, i.e., the effects of alternating single and multiple bonds. Conjugation has major effects on the properties of organic molecules. The present study will determine the degree to which this concept can be applied to inorganic chemistry, and in particular to compounds where metal atoms are essential participants in the conjugation. Metal atoms have more diverse modes of bonding than carbon atoms (including "delta" bonding), which raises the potential for conjugation in such systems to have even more profound effects than are found in organic systems. The present research will entail the synthesis of compounds designed to engage in conjugation, the elucidation of their structures, and measurements of their physical properties.