Publication

Bis(tetramethylpiperidino)aluminum halide adducts tmp2AlX.Do and tetrahaloaluminates of tricoordinated aluminum cations [tmp2Al(Do)]AlX4

1998
Article
Résumé

Upon treatment with Lewis bases Do (Do = pyridine bases or THF), the Lewis acids tmp2AlX (X = Cl, Br, I) are converted exclusively to the monoadducts tmp2AlX.Do. Crystal and mol. structure of these monoadducts were detd. The Al-X bonds of these addn. compds. are considerably elongated, indicating a tendency towards the formation of ionic species [tmp2Al(Do)]X. Due to the steric requirements of the bulky tmp ligands, addn. of an excess of the Lewis base does not force these compds. to form tetracoordinated Al cations [tmp2Al(Do)2]+ or pentacoordinated adducts tmp2AlX.Do2. Attempts to prep. ionic representatives by reaction of tmp2AlX.Do with "ate" complexes of comparatively low nucleophilicity [MY = NaBP4, AgBPh4, LiB(C6F5)4, AgBF4, AgOtos] result in phenylation products (e.g. tmp2AlPh and BPh3.py) or tetracoordinated addn. compds. tmp2AlY.Do (Y = anion). However, addn. of 1 equiv. of AlX3 (X = Br, I) initiates halide abstraction with formation of the ionic [tmp2Al(Do)]AlX4 species, as indicated by 27Al-NMR data and cond. measurements. Solid [tmp2Al(py)]AlI4 decomps. readily into tmpAlI2 and tmpAlI2.py. Addn. of non-polar aliph. solvents to solns. of [tmp2Al(Do)]AlX4 leads to slow decompn. into tmp2AlX and AlX3.Do. This also occurs in polar donor solvents, where compds. AlX3.Do are favored due to the formation of penta- or hexacoordinated species AlX3.Do.Solvn (n = 1, 2). Semiempirical AM1 calcns. reveal the gas-phase stability of the tricoordinated bis(tmp)aluminum cation in the salt [tmp2AlPy]AlCl4 as the only representative in a series of calcd. Al cations [(R2N)2A1Py]AlCl4 (R2N = Me2N, Et2N, iPr2N, tmp). According to these calcns., the stability of a given cation increases when tetrachloroaluminate is replaced by tetraiodoaluminate. Ab initio calcns. were performed on 2 cations [(H2N)2Al(Do)]+ (Do = NH3, py) and indicate very short Al-N bond lengths owing to ionic bonding contributions. [on SciFinder (R)]

À propos de ce résultat
Cette page est générée automatiquement et peut contenir des informations qui ne sont pas correctes, complètes, à jour ou pertinentes par rapport à votre recherche. Il en va de même pour toutes les autres pages de ce site. Veillez à vérifier les informations auprès des sources officielles de l'EPFL.

Graph Chatbot

Chattez avec Graph Search

Posez n’importe quelle question sur les cours, conférences, exercices, recherches, actualités, etc. de l’EPFL ou essayez les exemples de questions ci-dessous.

AVERTISSEMENT : Le chatbot Graph n'est pas programmé pour fournir des réponses explicites ou catégoriques à vos questions. Il transforme plutôt vos questions en demandes API qui sont distribuées aux différents services informatiques officiellement administrés par l'EPFL. Son but est uniquement de collecter et de recommander des références pertinentes à des contenus que vous pouvez explorer pour vous aider à répondre à vos questions.