This award in the Inorganic, Bioinorganic, and Organometallic Program provides continued support to Dr. Robert R. Holmes of the Chemistry Department, University of Massachusetts at Amherst, for the investigation of high valent silicon and phosphorus compounds. Anionic, hexacoordinated silicon compounds will be prepared and their characteristics will be compared to analogous phosphorus compounds. Acyclic, pentaoxy, anionic silicates will be studied in order to understand more concerning the initial steps in silanol polymerization. The structure and conformational properties of pentacoordinte phosphorus and silicon compunds containing rings varying in size from 6- to 8- membered will be studied, particularly as relevant to cAMP mechanisms. Also to be investigated is the mechanistic pathway for nucleophilic displacement reactions of tetracoordinate phosphorus and silicon. A wide range of tools will be used to characterize the compounds, including variable temperature NMR, X-ray diffraction, and molecular modeling. %%% Only recently has it become possible to compare the behavior of silicon compounds with five or six groups attached to silicon to the behavior of analogous phosphorus compounds. By comparing the details of reactions in which such compounds rearrange or lose the fifth or sixth group, it is possible to understand more about how spatial and electronic factors affect the chemistry of these compounds. This fundamental research project may help provide insight into the formation of silicon polymers or into the hydrolysis of nucleoside cyclic 3',5'-monophosphates, which play a central role in the regulation of cell metabolism.
