L'hydrure d'aluminium AlH3 ou alane est à la fois un matériau très important et une espèce chimique fascinante qui reçoit actuellement un regain d'intérêt lié à son utilisation potentielle pour différentes applications : (i) comme additif énergétique pour les ergols solides, (ii) comme agent réducteur dans les piles alcalines et (iii) comme source possible d'hydrogène pour des piles à combustibles basses températures. L'alane a une capacité de stockage volumique d'hydrogène de 0,148 g mL-1 soit deux fois plus que l'hydrogène liquide (0,07 g mL-1). Sa capacité de stockage d'hydrogène est supérieure à 10 % en masse. Malheureusement, le coût de production d'alane est élevé ce qui limite son utilisation notamment dans le domaine de la propulsion. L'objectif de cette thèse était d'optimiser la synthèse de l'alane α pur, variété cristalline considérée comme la plus stable et ainsi d'en réduire les coûts de production. Différentes méthodes de synthèse sous atmosphère contrôlée ont été mises en oeuvre. Il a été montré que le traitement thermique sous vide d'un complexe éthéré de AlH3 permettait de s'affranchir de l'utilisation de toluène et ainsi de réduire la quantité de solvants et de réactifs de 25 % tout en obtenant une phase α pure mise en évidence par DRX. Des essais de stabilisation contrôlés par ATD-ATG ont montré que la température de décomposition à pression atmosphérique de l'alane α était de 174 °C contre 160 °C pour la phase α non stabilisée. Une autre voie de synthèse, sans solvant et à l'aide d'une presse fabriquée au laboratoire a été explorée. Un plan d'expériences a été réalisé afin d'identifier les paramètres influant le plus sur le rendement en alane α et la pureté de la phase obtenue. L'alane synthétisé par ces différentes méthodes a été caractérisé par DRX, MEB, MET, ATD-ATG et ICP-OES. Un transfert technologique de la synthèse en solution a été opéré vers les partenaires industriels de ce travail. / Aluminium hydride or alane (AlH3) is a very important and fascinating material that draws increasing attention due to its potential uses: (i) as an energetic component in rocket propellants, (ii) as a reducing agent in alkali batteries and (iii) as a possible hydrogen source for low temperature fuel cells. It exhibits a density of 1,48 g cm-3, a volumetric hydrogen capacity of 0,148 g mL-1, that is more than twice as much as that of liquid hydrogen (0,07 g mL-1). Its hydrogen mass capacity slightly exceeds 10 wt.-%. Unfortunately, production of alane suffers from a high cost that hinders its opportunity to be an excellent candidate for propulsion. Moreover, only the α phase of alane is known to be stable enough to be stored and used. This work aims at developing cheaper methods for alane production while keeping a maximum selectivity towards the formation of α phase. Preparation using a classical organometallic synthesis in ether was implemented. An etherate complex was formed, the ether was removed under vacuum and finally an adequate thermal treatment led to pure α phase of alane as identified by powder X-ray diffraction. A toluene free synthesis method was implemented and resulted in a cost reduction of 25 %. The stability of the material was characterized through thermal analysis (DTA-TGA). The morphology and purity of the alane were characterized using TEM, SEM and ICP-OES. Alane was synthesized using doping compounds and resulted in a significant increase in the decomposition temperature from ca. 160 °C to ca. 174 °C. Syntheses without solvent were studied using a homemade reactor and following a design of experiment to identify the key parameter towards the highest yield in α-AlH3. The synthesis method in ether was transferred to our industrial partners.

Die vorliegende Arbeit ist in zwei Teile gegliedert und befasst sich im ersten Abschnitt mit der stöchiometrischen und katalytischen Aktivierung von Element-Element-Bindungen an NHC-stabilisierten Eisen(II)-Komplexen. Im Fokus der Untersuchungen steht hierbei sowohl die Isolierung und Charakterisierung neuartiger NHC-stabilisierter Eisen-Komplexe sowie deren Nutzung als Katalysatoren in der Hydrosilylierung von Carbonylverbindungen und der Hydrophosphanierung von Mehrfachbindungssystemen. Der zweite Teil dieser Arbeit ist der Reaktivität N-heterocyclischer Carbene gegenüber Hauptgruppenelement-Verbindungen wie beispielsweise Chlorsilanen, Stannanen, Phosphanen und Alanen gewidmet. Neben der Aufklärung mechanistischer Details der Reaktionen ist die übergangsmetallfreie Hydrodefluorierung von Fluoraromaten zentraler Bestandteil dieser Untersuchungen. / The present thesis is divided into two parts, the first of which is concerned with the stoichiometric and catalytic activation of element-element bonds at NHC-stabilized iron(II) complexes. The focus of these investigations is on the isolation and characterization of novel NHC-stabilized iron complexes and on their utilization as catalysts in the hydrosilylation of carbonyl compounds, as well as in the hydrophosphination of unsaturated hydrocarbons. The second part of this thesis addresses the reactivity of N-heterocyclic carbenes towards main-group element compounds such as chlorosilanes, stannanes, phosphines and alanes. Besides the elucidation of mechanistic details, the transition-metal-free hydrodefluorination of fluorinated aromatic compounds is a central part of this work

This thesis examines the interaction of hydrides of the group 13 metals aluminium and gallium with transition metal centres. Furthermore, a gallium-based system is developed which activates a wide range of E-H bonds, with the product of H₂ activation found to act as a catalyst for the reduction of CO₂ to a methanol derivative. Chapter 3 details the synthesis of a number of alane and gallane adducts of expanded-ring N-heterocyclic carbene (NHC) ligands, which are more strongly σ-donating and sterically shielding analogues of classical NHCs. These NHC adducts are found to be apposite for the formation of σ-alane and σ-gallane complexes at group 6 metal carbonyl fragments, which has allowed the characterisation of the first κ² σ-gallane complexes. The attempted formation of a terminally coordinated κ³ σ-alane complex leads instead to the isolation of a novel dinuclear cluster featuring both μ:κ¹,κ¹ and μ:κ²,κ² coordination to Mo(CO)₃ units. The work presented in Chapter 4 probes the interaction of the β-diketiminate stabilised gallane Dipp₂NacNacGaH₂ with transition metal carbonyls. Far from simply mimicking the chemistry of the alane congener Dipp₂NacNacAlH₂, which forms simple κ¹ and κ² σ-alane complexes, the gallane shows a marked propensity towards dehydrogenation and formation of direct M-Ga(I) bonds. This represents a rare mode of reactivity among group 13 hydrides, being unprecedented beyond boron chemistry, and provides a new route to M-Ga bond formation. Experimental and computational investigations of the mechanism suggest that initial Ga-H oxidative addition is facile, and is generally followed by rate-limiting loss of H₂. The reaction of Dipp2NacNacAlH2 with Co₂(CO)₂ is shown to yield an unusual alane complex which displays an unprecedented degree of Al-H activation in a σ-alane complex. Chapter 5 represents an extension of the work described in Chapter 5, investigating the interaction of Dipp₂NacNacMH₂ (M = Al, Ga) with cationic group 9 transition metal fragments supported by ancillary phosphine ligands. While attempts to isolate unsupported, cationic σ-alane complexes prove unsuccessful, Dipp₂NacNacGaH₂ readily binds to cationic rhodium and iridium centres, forming the first cationic σ-gallane complexes as well as cationic gallylene complexes resulting from complete Ga-H oxidative addition. The extent of Ga-H bond activation is shown to be markedly dependent on the nature of the phosphine co-ligands. In particular, a series of rhodium complexes is reported which represents snapshots of the oxidative addition process, from a Rh(I) σ-gallane complex to a Rh(III) gallylene dihydride, with two further complexes which are on the cusp of these two oxidation states. Described in Chapter 6 are the synthesis and reactivity studies of an ambiphilic system, Dipp₂NacNac′Ga(^tBu), featuring a three-coordinate gallium centre supported by a deprotonated NacNac ligand. The combination of this electrophilic gallium centre with the highly nucleophilic exocyclic alkene functionality facilitates the cooperative activation of protic, hydridic and apolar E-H bonds. Accordingly, molecules including H₂, NH₃, H₂S and SiH4 may be cleaved under mild conditions. Moreover, the hydride product of H₂ activation is shown to be a competent catalyst in conjunction with HBpin for the reduction of CO₂ to the methanol derivative MeOBpin.

Im Rahmen des BMBF-Projektes 'RevAl' wurden bereits bekannte Aminoalane in Bezug auf ihre physikalisch-chemischen Eigenschaften bei der chemischen Wasserstoffspeicherung untersucht. Es stellte sich heraus, dass die Freisetzung von Wasserstoff leicht und spontan realisierbar ist, wohingegen die reversible Speicherung (aufgrund von thermodynamischen Gesetzmässigkeiten) bei den gewählten Prozessbedingungen nicht realisierbar ist. Auch Modifikationen der bereits bekannten Aminoalane mit Neutralliganden und organischen Resten führten nicht zu den erhofften Eigenschaften. Jedoch wurde im Rahmen der Modifizierungsarbeiten die noch nicht beschriebene Verbindung 'Bis-Triphenylphosphinalan' strukturell und spektroskopisch charakterisiert. Weiterhin wurde diese im 9g-Maßstab hergestellte Verbindung für Reduktionsreaktionen von Carbonylderivaten eingesetzt, wobei sich, abhängig vom jeweiligen Carbonyl-Substrat, Unterschiede bei Umsatz und Ausbeute der Edukte bzw. Produkte ergaben. Weiterhin wurde die Reduktion von Benzaldehyd mit Bis-Triphenylphosphinalan NMR-spektroskopisch untersucht und eine Untermauerung des bereits postulierten Reduktionsmechanismus´ erhalten.

Investigation of the catalytic formation, reactivity and synthetic scope of sp³-gem-organodimetallic palladio(II)/main group metal (main group metal = tributylstannyl, dialkylalumino) alkane species has been carried out. Insight was expanded regarding the inter- and intramolecular reactivity of vinylmetallic reagents in presence of transition metal catalysts. New Pd-catalysed methodologies for carbon-carbon bond formation were developed, such as cyclopropanation of strained olefins, as well as tandem vinylalane arylation/1,2-methyl transfer and 1,2-diarylation. On the one hand, geminal π-allylpalladio(II)/tributylstannylalkane intermediates are produced by oxidative addition of Pd(0) catalysts to α-tributylstannylpropenyl acetate derivatives. They adopt ambiphilic behaviour depending on the transition metal pre-catalyst, presence or absence of phosphine ligands, and reaction temperature. In presence of tetrakis(triphenylphosphine)palladium(0) with additional bidentate ligand, the carbenoid reactivity of these gem-organobismetallic species is exposed by reaction with dimethyl malonate. Deuterium-labeling studies demonstrated sequential functionalisation of the C-Sn and C-Pd bonds. Conversely, phosphine-free catalyst bis(dibenzylideneacetone)palladium(0) uncovers metal-carbene reactivity, and dimerisation and strained alkene cyclopropanation reactions are observed. The nature of the palladium catalyst controls the reactivity of the carbenoid species. Finally, bis(cyclooctadienerhodium(I) chloride) catalytically activates the alkenylstannane moiety, leaving the allylic acetate leaving group available for further transformations. On the other hand, gem-disubstituted trifluoromethanesulfonyloxy- and iodopalladio(II)/ dialkylaluminoneopentane species are generated by intramolecular migratory insertion of 2,2-disubstituted-1-butenyldialkylalanes with σ-arylpalladium(II) triflate and iodide intermediates. Using excess Lewis-basic 1,4-diazabicyclo[2.2.2]octane, electron-rich tris(para-methoxyphenyl)phosphine ligand and acetonitrile as solvent, tandem arylation/1,2-alkyl migration from aluminum to carbon affords 7-substituted-1-ethyl-1-methylindanes containing an all-carbon quaternary stereogenic centre in good yields. This reaction is tolerant of 6-aryl methyl ethers, thioethers and trimethylsilanes. Deuterium labeling established that protiodealumination of the key neopentyl(methyl)aluminum triflate intermediate is caused by the acetonitrile solvent. The organodimetallic species in that study were shown to be configurationally stable, hence the stereospecificity of the process that proceeds via carbopalladation, transmetalation and reductive elimination of an alkylpalladium(II) intermediate. When applied to 1-naphthyl triflate-tethered vinylalanes, the same reaction conditions mediate stereospecific 1,2-diarylation, leading to 2,3,3a,4-tetrahydro-1H-cyclopenta[def]phenanthrenes in excellent yields. The influence of DABCO, tether length and solvent polarity was studied. Selective tandem arylation/1,2-methyl migration could also be achieved in non-polar solvent in absence of Lewis base. While steric properties took precedence over electronic considerations when inducing product selection, preagostic C-H···Pd interactions were postulated to facilitate 1,3-metal migration in the production of 1H-cyclopenta[def]phenanthrene derivatives.

Investigation of the catalytic formation, reactivity and synthetic scope of sp³-gem-organodimetallic palladio(II)/main group metal (main group metal = tributylstannyl, dialkylalumino) alkane species has been carried out. Insight was expanded regarding the inter- and intramolecular reactivity of vinylmetallic reagents in presence of transition metal catalysts. New Pd-catalysed methodologies for carbon-carbon bond formation were developed, such as cyclopropanation of strained olefins, as well as tandem vinylalane arylation/1,2-methyl transfer and 1,2-diarylation. On the one hand, geminal π-allylpalladio(II)/tributylstannylalkane intermediates are produced by oxidative addition of Pd(0) catalysts to α-tributylstannylpropenyl acetate derivatives. They adopt ambiphilic behaviour depending on the transition metal pre-catalyst, presence or absence of phosphine ligands, and reaction temperature. In presence of tetrakis(triphenylphosphine)palladium(0) with additional bidentate ligand, the carbenoid reactivity of these gem-organobismetallic species is exposed by reaction with dimethyl malonate. Deuterium-labeling studies demonstrated sequential functionalisation of the C-Sn and C-Pd bonds. Conversely, phosphine-free catalyst bis(dibenzylideneacetone)palladium(0) uncovers metal-carbene reactivity, and dimerisation and strained alkene cyclopropanation reactions are observed. The nature of the palladium catalyst controls the reactivity of the carbenoid species. Finally, bis(cyclooctadienerhodium(I) chloride) catalytically activates the alkenylstannane moiety, leaving the allylic acetate leaving group available for further transformations. On the other hand, gem-disubstituted trifluoromethanesulfonyloxy- and iodopalladio(II)/ dialkylaluminoneopentane species are generated by intramolecular migratory insertion of 2,2-disubstituted-1-butenyldialkylalanes with σ-arylpalladium(II) triflate and iodide intermediates. Using excess Lewis-basic 1,4-diazabicyclo[2.2.2]octane, electron-rich tris(para-methoxyphenyl)phosphine ligand and acetonitrile as solvent, tandem arylation/1,2-alkyl migration from aluminum to carbon affords 7-substituted-1-ethyl-1-methylindanes containing an all-carbon quaternary stereogenic centre in good yields. This reaction is tolerant of 6-aryl methyl ethers, thioethers and trimethylsilanes. Deuterium labeling established that protiodealumination of the key neopentyl(methyl)aluminum triflate intermediate is caused by the acetonitrile solvent. The organodimetallic species in that study were shown to be configurationally stable, hence the stereospecificity of the process that proceeds via carbopalladation, transmetalation and reductive elimination of an alkylpalladium(II) intermediate. When applied to 1-naphthyl triflate-tethered vinylalanes, the same reaction conditions mediate stereospecific 1,2-diarylation, leading to 2,3,3a,4-tetrahydro-1H-cyclopenta[def]phenanthrenes in excellent yields. The influence of DABCO, tether length and solvent polarity was studied. Selective tandem arylation/1,2-methyl migration could also be achieved in non-polar solvent in absence of Lewis base. While steric properties took precedence over electronic considerations when inducing product selection, preagostic C-H···Pd interactions were postulated to facilitate 1,3-metal migration in the production of 1H-cyclopenta[def]phenanthrene derivatives.