American Chemical Society
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Conformation of Heterocycles Controlled by the Existence of Unusual C−H···X Hydrogen Bonds:  Syntheses and Structure Determination of Aluminum Aryloxides

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journal contribution
posted on 2000-03-17, 00:00 authored by Bao-Tsan Ko, Ying-Chieh Chao, Chu-Chieh Lin
The reactions of AlMe3 in diethyl ether with 1 molar equiv of 2,2‘-methylenebis(4-methyl-6-tert-butylphenol) (MMBP-H2), 2,2‘-methylenebis(4,6-di-tert-butylphenol) (MDBP-H2), and 2,2‘-ethylidenebis(4,6-di-tert-butylphenol) (EDBP-H2) afford series of four-coordinate monomeric aluminum aryloxides, MeAl(O∼O)(OEt2), 13 (1, (O∼O) = MMBP; 2, (O∼O) = MDBP; 3, (O∼O) = EDBP). In THF, 1 molar equiv of EDBP-H2 reacts with AlMe3 to provide the THF-coordinated complex MeAl(EDBP)(THF) 4. However, in the absence of a coordinating solvent, the reaction of EDBP-H2 with AlMe3 yields the dimeric complex [MeAl(μ-EDBP)]2 (5). Complex 5 further reacts with Et4NCl, Et4NBr, and Ph3PO to afford the corresponding monomeric ionic complex [Et4N][MeAl(EDBP)(X)] (6, X = Cl; 7, X = Br) and the neutral complex [MeAl(EDBP)(OPPh3)] (8), respectively. Complexes 1, 2, 4 and 68 are subjected to X-ray structure analyses, and the solid state structures reveal that the conformations of the eight-membered heterocycles are governed by the formation of the unusual C−H···X hydrogen bonds.