Inspiration, Frustration, and Fascination: An Excursion into Low-Oxidation State Main Group Chemistry

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The Chemical Synthesis Program of the Chemistry Division supports the research project by Professor Gregory H. Robinson, a faculty member in the Department of Chemistry at The University of Georgia. Professor Robinson and his research team are studying the unique chemistry of low-oxidation state main group chemical compounds. The goal of this research is to exploit the unique stabilizing effects of organic bases (a class of compounds known as carbenes) on highly reactive main group molecules. For example, important molecules like disilicon (Si2) are only detectable at extremely low temperatures. In contrast, diphosphorus (P2) is typically only detectable at very high temperatures. The Robinson team has developed a means to stabilize molecules like Si2 and P2 (and many others) at room temperature, thus allowing the convenient study of the structure and reactivity of these important molecules. In particular, these researchers recently reported the first stable molecular examples of silicon oxides. This project investigates the synthesis of more ambitious silicon oxides. This chemistry has the potential for us to learn more about the silicon-oxygen interface with possible implications to computer chips and semiconductors. These researchers will also attempt to synthesize molecules containing large silicon and arsenic clusters. This project lies at the heart of main group chemistry, a field of inorganic chemistry that has traditionally received more emphasis in Europe. Outreach activities involving women and traditionally under-represented groups is central to this research. The students engaged in this work are acquiring valuable synthetic and experimental skills that make them highly valuable in the employment market.An ambitious program to explore challenging areas of low-oxidation main group chemistry is underway. The Robinson laboratory has developed N-heterocyclic carbenes (NHC or L:) and N-heterocyclic dicarbene (NHDC) derivatives that are being used as a unique platform from which many unusual low-oxidation state main group species can be synthetically stabilized. Major synthetic goals in this work include: (a) carbene-based multisilylenes; (b) carbene-stabilized silicon atom and clusters; (c) carbene-stabilized heteronuclear diatomic molecules [i.e., silicon carbides, diatomic III-V (13-15) species, arsenic phosphide (AsP)]. The recent report by this laboratory of carbene-stabilization of elusive silicon oxides (Nature Chem. 2015, 7, 509) has encouraged these workers to develop the long-sought molecular chemistry of SOx. Consequently, the syntheses of a series of carbene-stabilized silicon oxides (such as SiO, SiO2, Si2O, Si2O2, and Si3O6, etc.) and silicon hydrides [Si3H2 and Si2H2 (parent disilyne)] are being pursued. These carbene-stabilized silicon oxides may be further utilized to develop the corresponding transition-metal-modified derivatives and transfer silicon oxide clusters into organic or organometallic substrates. In addition, carbene-stabilized bis-silylenes are explored as potential transfer agents for the disilyne unit. The transition metal chemistry of carbene-stabilized zero-oxidation-state main group species are being examined in the work. Research findings from the Robinson laboratory have repeatedly challenged traditional theories of structure and bonding in inorganic chemistry and some of this has begun to appear in chemistry textbooks. Students engaged in this work are acquiring valuable synthetic, crystallographic, and computational skills. The Robinson laboratory has a positive record of extending the chemistry enterprise to larger segments of the human resource as a number of women and African Americans have been trained in his laboratory. In addition, Professor Robinson has developed a popular seminar course entitled "Molecules That Changed History".