Estimation of ring strain energies of organic and metallacycles and the mechanistic study of the reduction of ketones with 1-hydridosilatrane
De Lio, Ashley M.
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Previous estimations of the ring strain energies (RSEs) of organic rings have utilized the homodesmotic approach. The homodesmotic approach uses acyclic reference molecules to model the environments of the carbons in the ring. Unfortunately, this approach introduces many errors, in the form of uncanceled intramolecular interactions, especially as the degree of substitution of the ring increases. Here we discuss the RSEs of fluorocyclopropanes, fluorocyclohexanes, fluorocyclopropenes and fluorocyclobutenes predicted by this method. These RSE values along with previous studies have shown how undependable the homodesmotic approach is for calculating RSEs. The application of the semi-homodesmotic approach, which utilizes cyclic reference molecules to better model the ring environment, for fluorocyclopropanes and fluorocyclohexanes results in generally more chemically intuitive RSEs. Both the homodesmotic and semi-homodesmotic approaches have previously never been applied to metallacyclobutanes. Metallacyclobutanes are generally thought of as the intermediate of the Chauvin mechanism for olefin metathesis reactions. The study of the RSEs of Group 5 and Group 6 metallacyclobutanes can help us to better understand the thermodynamics of this mechanism and how RSE might play a role in it. The study of the reduction of ketones to alcohols with 1-hydridosilatrane also examines the thermodynamics of a mechanism, but this mechanism does not rely on RSE to progress. Here we discuss various mechanistic intermediates and transition states which help to create a reaction energy diagram. The analysis of the relative energies of the potential products shows that in the reduction of acetone using t-butoxide as initiator, the resulting isopropoxysilatrane/t-butoxide pair is more stable than the alternative t-butoxysilatrane/isopropoxide pair. QTAIM analysis was also utilized to determine the Lewis-acidity of the silicon during the mechanism to better understand how this affects the reaction.