Professor Peeter Burk, University of Tartu
Professor Holger Bettinger, University Tuebingen
Hydrogen can be found in many places from space to living creatures. Therefore the ability to add and release the nuclei of hydrogen atoms - protons, is an important property. The present dissertation concerns with amine-borane (R1R2R3N-BH3) and phosphine-borane (R1R2R3P-BH3) complexes and investigates the proton transfer reactions of the species. Such complexes are noteworthy because their hydrogen content is high (up to 19.6%) and they are able to release hydrogen both in the form of proton and dihydrogen (H2). This property can be used in energetics as the reversibility of the process would allow the compounds to be used as hydrogen storage materials.
One of the H2 release reactions characteristic to borane complexes is initiated by the addition of a proton. It was found that the boron moiety is clearly the most favorable protonation center and the resulting structure contains a loosely bound H2 molecule. The H2 release process is driven by entropy and can be very favorable energetically, depending on the substituent. It was also shown that the most probable deprotonation site in amine-boranes is the N-H group and in phosphine-boranes the P-H group.
In addition to hydrogen storage, those properties can be used to activate H2 to catalyze hydrogenation reactions. In the current thesis gas-phase complexation energies, acidities, basicities and energetics of the H2 release reaction for amine-borane and phosphines-borane complexes with a variety of different substituents are presented. Based on the results broader conclusions about the properties of such complexes were drawn.