The synthesis and structure of an anionic aluminabenzene, which is the first example of an aluminum-containing heterobenzene, are reported. The molecular structure of this aluminabenzene exhibits a planar six-membered ring, and the absence of any bond alternation between its unsaturated bonds is consistent with the structural criteria of aromaticity. Theoretical calculations and the NMR spectroscopic analysis of this anionic aluminabenzene furthermore suggest that, in addition to the aromatic conjugation of six π-electrons, an ambiphilic contribution from a Lewis acidic aluminum center and an anionic pentadienyl moiety are present. Due to this contribution, the aluminabenzene is able to react with Lewis bases such as 4-dimethylaminopyridine and electrophiles such as methyl iodide.
The interfacial tension of vegetable oil (soybean oil or coconut oil)/ water interface decreased with the increase of cyclodextrin (CD) concentration. The interfacial excess and interfacial area were calculated from the Gibbs' adsorption equation. The average number of CD molecules including a fatty acid residue of soybean oil at the interface was estimated at 2.4 for each of a-CD and S-CD. The average number of CD molecules complexed with a fatty acid residue of coconut oil was 1.8 for a-CD and 1.7 for S-CD. These results suggested that the CD molecules formed the inclusion complex with the triglyceride according to the chain length of fatty acid residue at the interface.
A stable bismabenzene was synthesized, isolated, and structurally characterized. The prospective aromaticity of this heavy benzene, bearing a sixth-row element, was examined by X-ray crystallography and NMR and UV-vis spectroscopy, as well as theoretical DFT calculations. Structural analysis of this bismabenzene revealed a planar ring containing unsaturated Bi-C and C-C bonds. As bond alternations could not be observed, these results are consistent with the formal criteria of aromaticity. Theoretical calculations also support the aromatic nature of this bismabenzene, which reacted with an alkyne to form the corresponding [4+2] cycloadduct, thus demonstrating a small yet tangible aromatic stabilization energy.
Aluminabenzene-rhodium and -iridium complexes were synthesized, in which the aluminum atom played as a proximal Lewis acidic site. Based on their structural analysis, aluminabenzene ligand could coordinate to Rh and Ir as a η-pentadienyl ligand. The Lewis acidic character of aluminum atom in aluminabenzene ligand was confirmed by treatment with 4-dimethylaminopyridine to form the corresponding Lewis acid-base complexes. In addition, the α-selective C-H borylation of triethylamine with the aluminabenzene-ligated iridium catalyst was demonstrated.
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