Lars Cuypers

Einfache Synthese von Alkylaluminium‐ und Alkylgalliumhydriden – Kristallstrukturen von [(Me3C)2GaH]3 und den neuartigen Sesquihydriden [(Me3C)2EH]2[EH2CMe3]2 (E = Al, Ga)

Die Synthese von praparativ wichtigen, sterisch hoch abgeschirmten Dialkylaluminiumhydriden R2AlH [R = CMe3, CH(SiMe3)2] gelingt durch Umsetzung der entsprechenden Trialkylaluminiumverbindungen mit dem Alanaddukt AlH3 · NMe2Et im Molverhaltnis 2 : 1. Monoalkylaluminiumdihydride sind auf diesem Wege nicht zuganglich. Als Hydrid-reichste Verbindung isolierten wir bei der Reaktion mit uberschussigem AlH3 das neuartige Sesquihydrid [(Me3C)2AlH]2[AlH2CMe3]2 (3), das im festen Zustand einen bisher nicht beobachteten Heterozyklus aus vier Aluminium- und vier Wasserstoffatomen aufweist. Auf gleichem Weg bildet sich durch Umsetzung von Tri(tert-butyl)gallan mit GaH3 · NMe2Et das Dialkylgalliumhydrid (Me3C)2GaH (4), das nach der Kristallstrukturbestimmung trimer mit Ga3H3-Heterozyklus vorliegt. Ein zu 3 analoges Galliumsesquihydrid [(Me3C)2GaH]2[GaH2CMe3]2 (5) entsteht bei Verwendung von uberschussigem GaH3. Facile Syntheses of Alkylaluminium and Alkylgallium Hydrides – Crystal Structures of [(Me3C)2GaH]3 and the Novel Sesquihydrides [(Me3C)2EH]2[EH2CMe3]2 (E = Al, Ga) The facile syntheses of some important, sterically highly shielded dialkylaluminium hydrides R2AlH [R = CMe3, CH(SiMe3)2] succeeded by the reaction of the corresponding trialkylaluminium compounds with the alane adduct AlH3 × NMe2Et in a 2 to 1 molar ratio. This route is not suitable for the synthesis of monoalkylaluminium dihydrides. An excess of AlH3 yielded the novel sesquihydride [(Me3C)2AlH]2[AlH2CMe3]2 (3) as the hydride richest compound which possesses an unprecedented heterocycle comprising four aluminium and four hydrogen atoms in the solid state. The dialkylgallium hydride (Me3C)2GaH (4) was formed on a similar route by the treatment of tri(tert-butyl)gallane with the adduct GaH3 · NMe2Et. As shown by a crystal structure determination, compound 4 is a trimer in the solid state possessing a Ga3H3 heterocycle. A gallium sesquihydride analogous to compound 3, [(Me3C)2GaH]2[GaH2CMe3]2 (5), was formed on employing an excess of GaH3.

Ga9(CMe3)9, an Important New Building Block in the Structural Chemistry of the Alkylelement(I) Compounds EnRn (E=B–In)

A simple preparative method has been employed for the synthesis of the novel cluster compound Ga9 (CMe3 )9 , which contains a tricapped trigonal prism of monovalent gallium atoms. Electron transfer processes were observed similar to those of polyboranes, leading to the the reversible formation of the corresponding radical anion.

Molecular self-assembly controlled by gallium-gallium single bonds-facile syntheses of macrocyclic octagallium compounds

Abstract Treatment of the digallane(4) derivative R2GaGaR2 (1) [R=CH(SiMe3)2] with the dicarboxylic acid muconic acid or with squaric acid yielded macrocyclic compounds (4 and 5, respectively) by retention of the GaGa single bonds and release of 2 equiv. of bis(trimethylsilyl)methane per formula unit of 1. Both products contain four GaGa single bonds connected by four dicarboxylato or diolato ligands. Large heterocycles resulted which contain 36 (4) and 20 atoms (5), respectively. The cavity of the macrocycle of 5 is filled by two n-pentane molecules. In contrast, two pentane molecules are located in hollows on the surface of the macrocycle of 4 in a supramolecular arrangement. They influence the molecular conformation significantly. The reaction with squaric acid gave a by-product (6) which also has eight gallium atoms in a heterocycle, but one GaGa bond was cleaved by oxidation and probably by the release of elemental hydrogen.

Verbrückende Koordination von Gallium–Gallium‐Bindungen durch Chelatliganden – Grenzen der Beständigkeit von Digallium‐Verbindungen

Die Umsetzungen von Bis[bis(trimethylsilyl)methyl]-di(μ-acetato)digallium(Ga–Ga) (2) mit Lithium-2-amido-1-methylbenzimidazol in den molaren Verhaltnissen von 1 : 1 bzw. 1 : 2 ergeben unter Abscheidung aquivalenter Mengen Lithiumacetat neue Digalliumverbindungen, in denen die Ga–Ga-Bindungen erhalten bleiben und jeweils von zwei Chelatliganden uberbruckt werden. Durch Ersatz nur eines Acetatrestes entsteht Verbindung 5 mit zwei unterschiedlichen verbruckenden Liganden, wobei die Benzimidazolgruppe uber die terminale Amidfunktion und das nicht an eine Methylgruppe gebundene Stickstoffatom des Heterozyklus koordiniert wird. Werden beide Acetatgruppen durch Benzimidazolreste ersetzt, lassen sich zwei Produkte nachweisen, in denen sich die Chelatliganden entweder durch eine Spiegelebene parallel zur Ga–Ga-Bindung (cis, 6) oder eine zweizahlige Achse senkrecht zur Element–Element-Bindung (trans, 7) ineinander uberfuhren lassen. 7 ist thermodynamisch stabiler und entsteht irreversibel beim Erhitzen des Gemisches. 5 und 7 werden kristallstrukturanalytisch charakterisiert, sie verfugen uber Ga-Atome mit chiraler Umgebung. Setzt man schwachere Donoren, wie Diphenyl(lithiomethyl)(piperidinomethyl)silan, ein, das uber sein carbanionisches Kohlenstoffatom und uber das sterisch abgeschirmte Piperidin-Stickstoffatom an Gallium koordinieren kann, bleibt die Ga–Ga-Bindung nicht erhalten. Wir isolieren die einkernige Verbindung 8, in der das Galliumatom an eine Bis(trimethylsilyl)methyl-Gruppe und zwei (Piperidinomethyl)silyl-Reste gebunden ist. Ferner wird uber die Synthese eines Dialkyl-bis(1,3-dionato)digallium-Derivates (9) berichtet, in dem die chelastisierenden 1,3-Dionato-Gruppen terminal an jeweils ein Ga-Atom der nicht verbruckten Ga–Ga-Bindung binden. Bridging Coordination of Gallium–Gallium Bonds by Chelating Ligands – Limitations of the Stability of Digallium Derivatives The reactions of bis[bis(trimethylsilyl)methyl]-di(μ-acetato)digallium(Ga–Ga) (2) with lithium-2-amido-1-methylbenzimidazole in the molar ratios of 1 to 1 or 1 to 2 yielded by the precipitation of lithium aceatate new digallium compounds, in which the intact Ga–Ga bonds were bridged by two chelating ligands. The replacement of only one acetato group gave compound 5, that possesses two different bridging ligands with the benzimidazole group coordinated by its terminal amido function and that nitrogen atom of the heterocycle which is not attached to a methyl group. If both acetato groups were replaced by imdazole ligands, two products were obtained, in which the chelates are transferred in each other either by a mirror plane parallel to the Ga–Ga bond (cis, 6) or by a twofold rotational axis perpendicular to the element–element bond (trans, 7). 7 is thermodynamically favored and was irreversibly formed by heating of the mixture. 5 and 7 were characterized by crystal structure determinations and have Ga atoms in a chiral environment. Weaker donor ligands such as diphenyl(lithiomethyl)(piperidinomethyl)silane, which in principal is able to coordinate via its carbanionic carbon atom and more weakly via its sterically shielded piperidino nitrogen atom, led to the cleavage of the Ga–Ga bond. The mononuclear compound 8 was isolated, in which the Ga atom is attached to one bis(trimethylsilyl)methyl group and two (piperidinomethyl)silyl substituents. Furthermore, the synthesis of a dialkyl-bis(1,3-dionato)digallium derivative (9) is reported, in which the chelating 1,3-dionato groups are terminally coordinated to the Ga atoms of the unsupported Ga–Ga bond.

Unexpected formation of gallium–gallium single bonds by irradiation of the hydride [(Me3C)2GaH]3

Di(tert-butyl)gallium hydride 1 dismutates partially in solution forming tri(tert-butyl)gallium 2 and the sesquihydride [(Me3C)2GaH]2[H2GaCMe3]2 (3). The loss of tert-butyl radicals upon irradiation of this mixture with day light or an UV lamp gave the hexagallium compound (Me3CGaGaCMe3)2(μ-H)2[μ-H2Ga(CMe3)2]2 (4), which possesses two Ga–Ga single bonds. These Ga2 groups are bridged by two hydrogen atoms to give a six-membered Ga4H2 heterocycle. Couples of opposite gallium atoms of this heterocycle are bridged via Ga–H–Ga 3c–2e bonds by two H2Ga(CMe3)2 ligands, which are situated above and below the molecular plane. Compound 4 may be described as a hypho-hexagallane(14) cluster compound.