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FLP-type nitrile activation and cyclic ether ring-opening by halo-borane nonagermanide-cluster Lewis acid–base pairs

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Abstract

Even though homoatomic nine-atom germanium clusters are known for two decades, their chemical properties are still rarely investigated. We now discovered that Zintl ion main group-element clusters possess a reactive lone pair of electrons, and we show a new pathway to bind ligands with functional groups to the [Ge9] cluster core through Ge–C bond formation. We report on the reactivity of [Ge9{Si(TMS)3}2]2− (TMS = trimethylsilyl) towards a series of Lewis acidic bromo-boranes. The reaction of [Ge9{Si(TMS)3}2]2− and DABo-tol–Br (DAB = 1,3,2-diazaborolidine; o-tol = 2-methylphenyl) resulted, depending on the reaction protocol, either in the formation of [Ge9{Si(TMS)3}2DABo-tol] (1a) with direct Ge–B interactions, or in [Ge9{Si(TMS)3}2(CH2)4O–DABo-tol] (2a) featuring a ring-opened thf moiety. Ring opening reactions occur for all bulkier DABR–Br [R: o-xyl (2,6-dimethylphenyl), Mes (2,4,6-trimethylphenyl), Dipp (2,6-diisopropylphenyl)], DAB(II)Dipp–Br and acyclic (iPr2N)2BBr without Ge–B bond formation as shown for the structural characterization of the ring-opened products of thf (3, 4) and trimethylene oxide (5). In contrast to thf, the activation of CH3CN requires the simultaneous presence of Lewis-acid and Lewis-basic reactants allowing the formation of [Ge9{Si(TMS)3}2CH3C[double bond, length as m-dash]N–DABMes] (6a). Within the presented compounds, 3 and 4 show an unusual substitution pattern of the three ligands at the [Ge9] core in the solid state. The [Ge9] cluster/borane systems correspond to intermolecular frustrated Lewis pairs (FLPs), in which the [Ge9] cluster with several lone pairs represents the Lewis base, and the borane is the Lewis acid.

Graphical abstract: FLP-type nitrile activation and cyclic ether ring-opening by halo-borane nonagermanide-cluster Lewis acid–base pairs

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Article information


Submitted
09 Feb 2021
Accepted
02 Apr 2021
First published
07 Apr 2021

This article is Open Access
All publication charges for this article have been paid for by the Royal Society of Chemistry

Chem. Sci., 2021, Advance Article
Article type
Edge Article

FLP-type nitrile activation and cyclic ether ring-opening by halo-borane nonagermanide-cluster Lewis acid–base pairs

C. Wallach, F. S. Geitner and T. F. Fässler, Chem. Sci., 2021, Advance Article , DOI: 10.1039/D1SC00811K

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