Sterically crowded aryloxides of aluminum: intramolecular coordination of bidentate ligands

Reactions of (BHT)2Al(H)(Et2O) (BHT-H=HOC6H2-2,6-tBu2-4-Me) with HOCH2CH2EMex (E=O, S, x=1; E=N, x=2) yield dimeric species, [(BHT)Al(H)(μ-OCH2CH2NMe2)]2 (2), [(BHT)Al(H)(μ-OCH2CH2OMe)]2 (3), [(BHT)Al(H)(μ-OCH2CH2SMe)]2 (4), respectively or [(BHT)Al(OCH2CH2NMe2)(μ-OCH2CH2NMe2)]2 (5), [(BHT)Al(OCH2CH2OMe)(μ-OCH2CH2OMe)]2 (6) and [(BHT)Al(OCH2CH2SMe)(μ-OCH2CH2SMe)]2 (7), respectively, depending on the stoichiometry of the reaction. The non-bridged donor atoms interact intramolecularly to form five-coordinate aluminum centers. A mixture of (BHT)Li(Et2O) and (BHT)2Al(H)(Et2O), formed from the reaction of LiAlH4 and BHT-H, reacts with the aforementioned alcohols to yield the monomeric structures (BHT)2Al(μ-OCH2CH2NMe2)2Li (8), (BHT)2Al(μ-OCH2CH2OMe)2Li (9), (BHT)2Al(μ-OCH2CH2SMe)2Li (10), respectively. If the reaction is carried out with an excess of HOCH2CH2SMe, the solvate of compound 10 is formed, (BHT)2Al(μ-OCH2CH2SMe)2Li(HOCH2CH2SMe) (11). The lithium cation in compounds 8–11 is stabilized in the structure by formation of bonds with both the anionic oxygens as well as the neutral donor ligands. The bond valencies have been calculated for Al and Li in compounds 8 and 11.