A study of the gas phase ion chemistry of boranes and borohydride ions in a flowing afterglow
Abstract
The research discussed in this thesis pertains to the thermochemistry, reactivity, and structure of gas-phase borohydride ions. Three areas of gas-phase ion chemistry are examined in this thesis: borane anion affinities, partially-solvated borohydride ions, and Lewis base complexes of boranes. The hydride affinities of several boranes including BH$\sb3$ were found to span a range of approximately 30 kcal/mol. The hydride affinity of BH$\sb3$ (79.5 kcal/mol) is near the middle of this range. Whether substituted boranes have a higher or lower hydride affinity than the archetype borohydride ion can be readily explained in terms of substituent effects on borane and borohydride ion stability. Other borane anion-binding energies were estimated and are also discussed. We have synthesized and characterized a number of partially-solvated borohydride ions. These ions are weakly bound cluster ions. We have also investigated the reactivity of these ions toward carbonyl compounds in order to examine the possible catalytic effect of a single protic solvent molecule. Furthermore, we have employed ab initio molecular orbital methods in order to investigate the detailed structure of several borohydride-protic solvent cluster ions and to compute solvation enthalpies for these ions. We have also investigated borane-Lewis base complexes. These reagents were used in ion-molecule reactions for the synthesis of BH$\sb4\sp{-}$, polyborohydride ions, and various substituted borohydride ions. In the case of the dimethyl sulfide complex of borane, we have investigated the anion derived from deprotonation of this complex. The proton affinity of this ion was estimated to be 376.0 kcal/mol. This value is supported by high-level ab initio calculations.
Degree
Ph.D.
Advisors
Squires, Purdue University.
Subject Area
Organic chemistry
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