A Theoretical Study of Silylamides

Lane, Thomas Howard (1990). A Theoretical Study of Silylamides. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000fc59

Abstract

Silylation is an important reaction in organosilicon and related chemistries. It involves the reversible exchange of an active hydrogen for a silyl group, generally trimethysilyl, which dramatically alters the physical and chemical characteristics of the original molecule. Among the various classes of silylating agents available, the silylamides are the most interesting. This class of silylating agent has demonstrated thermodynamic silylating power which spans over seven orders of magnitude. The structural complexity of these materials appears to be related to their reaotivity and includes both tautomeric and rotameric species. The work presented here, explores this novel class of materials. The hindered rotation of silylamides, the 1,3-migration of silicon between nitrogen and oxygen in these materials, and some of their conformational effects on the silylation process are examined using both semiempirical quantum mechanical methods and ah initio techniques.

The computational data presented here, supports what is known about the rotational and tautomeric behaviour of silylamides and silylformamide. We have successfully calculated the torsional barrier for a series of materials and explained some of their unique electronic and chemical characteristics.

The activated 5-coordinate intermediate for the 1,3- migration of silicon between nitrogen and oxygen has been characterized and an estimated activation energy for the process given.

The reaction of N-silylformamide and 0-silylformimide with water was studied. Those data suggest that the O- silylimidate tautomer is the preferred tautomeric species for the silylation of water. A calculated energy profile for each reaction is given and explained.

Several semiempirical molecular orbital methods were evaluated during this work and those findings are described and compared to ab initio results.

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