Werner Uhl

Geminal phosphorus/aluminum-based frustrated lewis pairs: C−H versus C≡C activation and CO2 fixation.

Catch it! Geminal phosphorus/aluminum-based frustrated Lewis pairs (FLPs) are easily obtained by hydroalumination of alkynylphosphines. These FLPs can activate terminal acetylenes by two competitive pathways, which were analyzed by DFT calculations, and they can bind carbon dioxide reversibly. Therefore, alongside polyfluorinated boranes, alanes are also ideal Lewis acids for FLP chemistry.

Synthese und Molekülstruktur des Tetrakis[bis(trimethylsilyl)methyl]digallans(4) mit GalliumGallium-Bindung

Abstract Reaction of Ga2Br4·2dioxane with four equivalents of bis(trimethylsilyl)methyllithium yields tetrakis[bis(trimethylsilyl)methyl]digallane(4) (1), which precipitates from n-pentane as well-shaped yellow crystals. Compound 1 is isotypic to the recently synthesized dialane(4) analogue; the metalmetal bond in 1 is found to be shortened by 12 pm compared with that of the aluminium derivative. Both molecules show almost planar cores. UV/VIS spectra display absorptions at ∼ 370 nm assigned to the metalmetal bonds.

Tetrakis[bis(trimethylsilyl)methyl]diindan(4) mit IndiumIndium-Bindung

Abstract The reaction of In 2 Br 4 · 2TMEDA with lithium-bis(trimethylsilyl)methyl forms tetrakis[bis(trimethylsilyl)methyl]diindane(4) ( 1 ), having an indiumindium bond and precipitating from n-pentane as orange-red crystals. Though the molecular structure of 1 closely resembles that of the aluminium and gallium analogues, 1 is not isotypic to these compounds. The metalmetal distance in 1 is 282.8 pm. (TMEDA)Li(μ-Br) 2 In[CH(Sime 3 ) 2 ] 2 , also characterized by X-ray diffraction analysis, and In[CH(Sime 3 ) 2 ] 3 were isolated as by-products.

Tetrakis[bis(trimethylsilyl)methyl]dialan(4), eine Verbindung mit Aluminium-Aluminium-Bindung

Abstract The reaction of chloro-bis[bis(trimethylsilyl)methyl]alane (1) with potassium yields the title compound 2.2 crystallizes in the triclinic space group P1̄ and shows an aluminium -aluminium bond length of 266.0(1) pm. The core of the molecule is almost planar.

Dimeric aluminum–phosphorus compounds as masked frustrated Lewis pairs for small molecule activation

Hydroalumination of aryldialkynylphosphines RP(C≡C-(t)Bu)(2) (R = Ph, Mes) with equimolar quantities of diethylaluminum hydride afforded mixed alkenyl-alkynyl cyclic dimers in which the dative aluminum-phosphorus bonds are geminal to the exocyclic alkenyl groups. Addition of triethylaluminum to isolated 1 (R = Ph) or to the in situ generated species (R = Mes) caused diethylaluminum ethynide elimination to yield the arylethylphosphorus dimers 2 and 3. These possess a chair-like Al(2)C(2)P(2) heterocycle with intermolecular Al-P interactions. The boat conformation (4) was obtained by the reaction of (t)Bu-P(C≡C-(t)Bu)(2) with di(tert-butyl)aluminum hydride. Despite being dimeric, 2 behaves as a frustrated Lewis pair and activates small molecules. The reaction with carbon dioxide gave cis/trans isomeric AlPC(2)O heterocycles that differ only by the configuration of the exocyclic alkenyl unit. Four isomers resulted from the reaction with phenyl isocyanate. This is caused by cis/trans isomerization of the initial C=O adduct and subsequent rearrangement to the AlPC(2)N heterocycle, being the C=N adduct.

The reactivity of organoelement compounds with aluminium—aluminium, gallium—gallium and indium—indium bonds

Abstract Organoelement derivatives with aluminium—aluminium, gallium—gallium and indium—indium bonds were synthesized for the first time in our group eight years ago. They show a remarkable and unprecedented chemical reactivity and up to now six different types of reaction have been found, which are summarized in this review article: (i) The formation of adducts is observed with sterically less shielded Lewis-bases like H − or Br − . (ii) The treatment with strong reducing agents like the alkali metals or some alkyllithium derivatives yields radical anions with le-M-M π bonds. (iii) Sterically more shielded bases give a deprotonation of the substituent with the formation of heterocycles. (iv) Insertion reactions into the element—element bonds could be realized with atoms, whole molecules or molecular fragments. (v) A metathesis reaction with a ditellurium derivative gives a monomeric organo gallium telluride. (vi) An exchange of two alkyl substituents with the preservation of the element—element bond is observed by the reaction with carboxylic acids.

Dialan-Radikalanionen [R2Al-AlR2].−

Abstract Tetrakis[bis(trimethylsilyl)methyl]dialane(4) ( 1 ) with an AlAl bond reacts with sodium or potassium in 1,2-dimethoxyethane to yield dar

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.

In4{C(SiMe3)3}4 mit In4-tetraeder und In4Se4{C(SiMe3)3}4 mit In4Se4-heterocubanstruktur

The reaction of InIBr with LiC(SiMe3)3. 2THF yields the In(I) alkyl In4{C(SiMe3)3}4 1 in 70% yield. 1 was characterized by a crystal structure determination showing a nearly undistorted In4 tetrahedron with mean In-In distances of 300.2(1) pm. Reaction of 1 with elemental Se gives In4Se4{C(SiMe3)3}4 2 with a slightly distorted In4Se4 hetero cubane structure.

Das tetraalkyldigallan-radikalanion [R2Ga−GaR2]− [R CH(SiMe3)2] mit langer einelektron-π-bindung

Abstract The electron transfer reaction of [(Me 3 Si) 2 CH] 2 GaGa[CH(SiMe 3 ) 2 ] 2 1 with ethyl lithium yields thin layers of dark red (almost black) crystals of the corresponding radical anion [R 2 Ga-GaR 2 ]- 2 with [Li(TMEDA) 2 ] + , [Li(DME) 3 ] + or [Li(trimethyltriazinane) 2 ] + as a counterion. EPR spectroscopic study of 2 reveals temperature-dependent 69 Ga, 71 Ga and 29 Si hyperfine splitting with extreme line broadening. Together with the unusually large abetaute values α( 69,71 Ga) > 5.7 mT at 300 K the pronounced temperature dependence of the coupling constants suggests a shallow energy minimum for the planar structure of the [Li(triazinane) 2 ] + salt observed by X-ray crystallography. The GaGa bond length amounts to 240.1(1) pm, which is 14 pm shorter than in neutral 1 which has a GaGa single bond.