Investigation of low energy conformations of substituted silphenylenes by computational techniques

Conformational searches of l, 4-bis(dimethylhydroxysilyl)benzene and l, 4-bis(dimethylhydroxysilyl)2, 3, 5, 6-tetramethylbenzene were conducted in order to determine the global minimum conformations of these materials. Dimethylsiloxy linkages between phenyl and tetramethylphenyl were also investigated to gain insight into possible differences in properties between polymers based on these two silphenylenes. Searches were performed using InsightII's Discover module and the consistent valence force field. Results for the diphenyl linkage (unhindered system) showed an unexpected global minimum conformation that may help to explain some of the thermal properties previously reported for this crystalline polymer. Results for the di-tetramethylphenyl linkage (hindered system) were consistent with other studies investigating diphenyl linkages, however, the energy contour for this system suggested a higher rotational energy compared to the former system. These results have encouraged us to proceed with the synthesis of the hindered system.