Group 3 and Group 13 Metal Hydride Compounds

The aim of this thesis was to synthesize (and characterize) group 3 and group 13 metal alkyl and hydride complexes. These complexes were supported by aminopyridinato, guanidinato and phenolato ligands. Guanidinato ligand stabilized aluminum alkyl complexes were synthesized through alkane elimination. Aminopyridinato and guanidinato ligand stabilized aluminum hydride complexes were synthesized using H2 elimination. Mononuclear structures featuring tetrahedral coordination of the central aluminum atom were observed for the guanidinato ligand stabilized aluminum dialkyl complexes. The (Al)N-C-N(Al) bond angles in the corresponding complexes were determined using structural data. A decrease in the angle with increasing steric bulk of the ligands backbone was observed. Studies regarding the dependency of the used aminopyridinato and guanidinato ligand on the structure and stability of aluminum hydride complexes were carried out. The prepared aminopyridinato ligand stabilized alane complex adopts a binuclear, double hydride bridged structure. The aluminum atoms are five-coordinated in this compound. This complex is thermally unstable. Intramolecular ligand redistribution reactions were observed even at room temperature resulting in a mononuclear aluminum monohydride complex stabilized by two aminopyridinato ligands. Again, the aluminum atom was five-coordinated in this compound. To obtain thermally stable complexes, guanidinato ligand stabilized aluminum hydride complexes were synthesized. Based on available literature, guanidinato ligands are not likely prone to follow ligand transfer reactions. If the guanidine PipGuH (N,N'-bis(2,6-diisopropylphenyl)piperidine-1-carboximidamide) is reacted with alane, an isostructural (to the aminopyridinato ligand stabilized aluminum hydride complex) binuclear, double hydride bridged complex was observed. Moreover, the reaction of a bulky guanidine ligand with lithiumalanate was studied. Formation of a novel guanidinato ligand stabilized alanate complex (81 % yield) was observed. This is a rare example of a σ-alane lithium complex. Guanidinato or phenolato ligand stabilized lanthanoid dialkyl complexes were synthesized starting from lanthanoid trialkyl complexes. These trialkyls were prepared by salt metathesis reaction of lithium alkyls with lanthanoid trichlorides. Hydrogenolysis with H2 was used to convert the guanidinato ligand stabilized yttrium dialkyl complex into a trinuclear guanidinato ligand stabilized yttrium hexahydride cluster compound. This cluster compound was studied by single crystal X-ray structure analysis and NMR spectroscopy. Highly dynamic behavior of the hydrides and the guanidinato ligands was observed by variable temperature 1H NMR spectroscopy. A heterobimetallic lutetium–tungsten polyhydride cluster compound was prepared by reaction of bis cyclopentadienyl tungsten dihydride with a phenolato ligand stabilized lutetium dialkyl complex. Cluster formation proceeded via C–H bond activation of the Cp ligands that stabilize the transition metal-containing educt followed by alkane elimination. Single crystal structure analysis revealed a cluster composed of three tungsten atoms and two lutetium atoms. Each of the two Lu atoms is double bridged by two µ2-hydrides and two µ3-hydrides to the W atoms. This finding was confirmed by 1H NMR spectroscopy. In addition, the first examples of ternary rare earth–transition metal polyhydride cluster compounds were synthesized starting from a phenolato ligand stabilized lutetium monoalkyl complex featuring a direct Lu–Re bond. Cluster formation proceeded by reaction with bis cyclopentadienyl tungsten dihydride or the analogue molybdenum compound. For both cluster compounds, the average yield was 50 %. Both of the ternary compounds were characterized by single crystal structure analysis and NMR spectroscopy. These studies revealed isostructural clusters featuring two lutetium atoms, either two tungsten or two molybdenum atoms and a rhenium atom. The W and Mo atoms, respectively, are bridged by two µ2-hydrides to the lutetium atoms. Quantum chemical calculations of the electronic structure, based on a simplified model (substituting H for the tert-butyl groups of the phenolato ligand) showed ionic W–H∙∙∙Lu interactions and a covalent, polar Lu–Re bond.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Universität Bayreuth

Year

2013

Author dc:creator

• Bauer, Tobias

Contributors dc:contributor

• Kempe, Rhett

Repository record source_url

https://epub.uni-bayreuth.de/id/eprint/96/

OAI identifier oai:identifier

oai:epub.uni-bayreuth.de:96