Thomas Spies

THE REACTIONS OF R2GA-GAR2 AND R2IN-INR2 R = CH(SIME3)2 WITH PROTIC REAGENTS : SUBSTITUENT EXCHANGE VERSUS CLEAVAGE OF THE ELEMENT-ELEMENT BOND

Tetrakis[bis(trimethylsilyl)methyl]digallane(4) (1) with a Ga−Ga single bond and the corresponding diindane(4) 2 with an In−In single bond were treated with different protic reagents: tert-Butyl alcohol did not react with 1 at all, while phenol gave a mixture of unknown products, which could not be separated. The more acidic pentafluorophenol did not react as an acid, but C−F bonds were cleaved to form almost quantitatively the dimer (R2GaF)25, which was characterized by a crystal-structure determination. Water and 1 yielded the dimeric dialkylgallium hydroxide 6. The Ga−Ga bond was also cleaved by the reaction of 1 with durylthiophenol (duryl = 2,3,5,6-tetramethylphenyl), which gave two main products: R2Ga(SDuryl) 7 and RGa(SDuryl)28. In contrast, the chelating acid dibenzoylmethane reacted by means of a substituent exchange, with the release of two equiv. of bis(trimethylsilyl)methane for each formula unit of 1, to form 9, in which the Ga−Ga bond is retained and each chelating 1,3-diphenyl-1,3-propanedionato ligand is in a terminal position bonded to only one Ga atom, in more than 80% yield. The Ga−Ga bond is shortened [244.1(1) pm] compared to that in the starting compound tetraalkyldigallane(4) 1. The In−In bond of diindane(4) 2 is, however, cleaved in a similar reaction with dibenzoylmethane, and only the fragmentation product dialkyl(1,3-diphenyl-1,3-propanedionato)indium 10 could be isolated.

Synthesis and structure of an alkylgallium bridged [1,1]ferrocenophane

Abstract A gallium bridged [1,1]ferrocenophane (2) was obtained by the reaction of 1,1′-dilithio ferrocene with the alkyltrichlorogallate [Li(THF)]+[R–GaCl3]− [R=CH(SiMe3)2] (1). The crystal structure determination of the orange–red compound 2 revealed two trigonal planar coordinated, coordinatively unsaturated bridging gallium atoms, each of which is attached to two carbon atoms of different ferrocene molecules and the inner carbon atom of the bis(trimethylsilyl)methyl substituent.

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.