Molekulare Magnesiumhydride und bimetallische Lithiumhydridoaluminate

  • Molecular magnesium hydrides and bimetallic lithium hydrido aluminates

Lemmerz, Lara Elisa; Okuda, Jun (Thesis advisor); Mulvey, Robert Emmit (Thesis advisor)

Aachen (2019)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2019

Abstract

The aim of this work is the synthesis, characterization and systematic investigation of the reactivity of magnesium hydrides. Therefore, magnesium silyls and magnesium silyl amides are synthesized and their reactivity towards hydrosilanes and dihydrogen is studied to investigate whether these compounds are suitable for the synthesis of magnesium hydrides. Moreover, the detailed investigation of the reactivity of these magnesium silyls extends the knowledge of the magnesium silicon bond. The Me3TACD stabilized magnesium silyl [(Me3TACD)Mg(SiPh3)] undergoes silyl silane exchange with hydrosilanes, which is until now just known for transition metal silyls. Furthermore, [(Me3TACD)Mg(SiPh3)] reacts with one equivalent pyridine to the 1,4-insertion product [(Me3TACD)Mg(NC5H5-4-SiPh3)] and with an excess of pyridine to the magnesium 1,4 dihydropyridine complex [(Me3TACD)Mg(NC5H6)] and 4 triphenylsilyl pyridine as byproduct. The magnesium dihydropyridine is active in the hydroboration of pyridine with pinacolborane. The ionic Me4TACD stabilized magnesium silyl [(Me4TACD)Mg(SiPh3)][A] ([A] = [Ph2CCH2SiPh3]; [B(3,5-Cl2-C6H3)4]) reacts also with hydrosilanes in a silyl silane exchange, whereas the ionic Me4TACD stabilized magnesium silyl amide [(Me4TACD)Mg(TMDS)][B(3,5-Cl2-C6H3)4] shows no reaction with hydrosilanes. The Me4TACD stabilized mixed magnesium amido hydride [(Me4TACD)Mg($\mu$-H)2Mg(HMDS)2] is obtained starting from [Mg(HMDS)2(THF)2], the macrocyclic Me4TACD ligand and phenylsilane. The ionic magnesium hydride dimer [(Me4TACD)2Mg2($\mu$-H)2][B(3,5-Me2-C6H3)4]2 can be synthesized by protonolysis with [NEt3H][B(3,5-Me2-C6H3)4]. The reactivity of the ionic magnesium hydride dimer is investigated in detail and four different reaction types are found: lewis acid base addition, protonolysis, redox reaction and hydrometallation. Another important part of this work is the synthesis of bimetallic lithium amido hydrido aluminates stabilized by different donor ligands. Using the macrocyclic Me3TACD ligand leads to the synthesis of the lithium aluminum adduct [(Me3TACD·AlHiBu2)Li(THF)] and the lithium boron adduct [(Me3TACD·BHPin)Li]. The solid state structures of the adducts show the coordination of the aluminum hydride and the boron hydride to the amido nitrogen atoms of the ligands, but no lithium hydride bonds are present. Different lithium amido hydrido aluminates are synthesized using PMDTA, Diglyme or DABCO as donor ligands. The lithium amido hydrido aluminates catalyze the hydroboration of carbonyls with pinacolborane. Thereby, a strong influence of the donor ligands on the catalytic activity is observed and can be ascribed to the different structures in solid state and in solution. The lithium amido hydrido aluminates contain a basic 2,2,6,6-tetramethylpiperidine ligand and a nucleophilic hydride ligand resulting in a bifunctional reactivity towards substrates containing acidic hydrogen atoms.

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