Part 1: A theoretical study of the 1,3-dipolar cycloaddition of nitrone and fulminic acid with substituted ethylenes. Part 2: A theoretical study of metallabenzenes

This dissertation contains results of two projects. The first project is a theoretically study of the 1,3-dipolar cycloaddition; the second, a theoretical study of metallabenzenes.; The first part of this dissertation uses molecular orbital calculations to examine the electronic effects involved the regioselectivity in the 1,3-dipolar cycloaddition reaction of nitrone and fulminic acid. The substituted ethylene dipolarophiles were selected to represent a variety of electron donating/withdrawing ability: amino, methyl, carbaldehyde (both in the s-cis and the s-trans conformations) and nitrile. The reactions were all asynchronous, with early transition states. The regioselectivity is correlated with the ability of the substituent to donate or withdraw electrons. With electron donating substituents, the substituent was directed preferentially to the oxygen end of the dipole. This shifts toward the other regioisomer as the electron withdrawing ability of the substituent increased. Comparing the results obtained in this study with frontier molecular orbital theory results, these results are more accurate than those obtained in earlier studies. The results were also analyzed using the Hammett {dollar}sigma{dollar} values, giving no correlation.; The second part of this dissertation involves calculation of the relative stability of metallabenzenes and the corresponding {dollar}etasp5{dollar} complexes. This project will examine the relative thermochemical stabilities to determine if it is at all feasible to prepare specific metallabenzenes. Examination of the following transition metals: manganese, iron, rhenium, ruthenium, technetium, osmium, cobalt, rhodium, iridium, nickel, palladium, and platinum; was used to determine trends in the stability. As one moves across the period or down a group the metallabenzene becomes more stable. In addition, natural bonding orbital analysis shows that most of the metallabenzenes are bonded into a metallacycle. The exceptions are manganese and iron using RHF.