Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 27, Issue 16, Pages 5120-5124Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.202005493
Keywords
aluminum; anti-van ’ t Hoff– Le Bel; calix[4]pyrrole; Lewis acid; planar aluminate
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Funding
- DFG (Emmy-Noether program) [GR 5007/2-1]
- Foundation of German Business (sdw)
- DFG
- Projekt DEAL
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The study investigated the properties of square-planar aluminum anions and the impact of ligand modification through a systematic screening process. The results revealed that different ligand structures can lead to opposing trends in the coordination preferences of aluminum anions, potentially allowing for mode-selective binding in catalytic reactions for control of reaction rates.
Structural constraint represents an attractive tool to modify p-block element properties without the need for unusual oxidation or valence states. The recently reported methyl-calix[4]pyrrolato aluminate established the effect of forcing a tetrahedral aluminum anion into a square-planar coordination mode. However, the generality of this structural motif and any consequence of ligand modification remained open. Herein, a systematic ligand screening was launched, and the class of square-planar aluminum anions was extended by two derivatives that differ in the meso-substitution at the calix[4]pyrrolato ligand. Strikingly, this modification provoked opposing trends in the preference for a Lewis acidic binding mode with sigma-donors versus the aluminum-ligand cooperative binding mode with carbonyls. Insights into the origin of these counterintuitive experimental observations were provided by computation and bond analysis. Importantly, this rationale might allow to exploit mode-selective binding for catalytic rate control.
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