Intramolecular C-H...O hydrogen bond controlling the conformation of heterocycles: synthesis, structure and catalytic reactivity of aluminum aryloxides

摘要

The reactions of R_2AlX with one equivalent of 2,2'-methylene-bis-(4,6-di-tert-butylphenol) (MDBP-H_2) or 2,2'-methylene-bis-(4-methyl-6-tert-butylphenol) (MMBP-H_2) in oxygenated solvent afford monomeric four-coordinated compounds, XA1(MDBP)(S), 1-5 (1: R = Me, X = Br, S = Et_2O; 2: R = Et, X = Cl, S = Et_2O; 3: R = Me, X = Br, S = THF; 4: R = Et, X = Cl, S = THF; 5: R = X = Et, S = Et_2O) or XA1(MMBP)(S), 6-8 (6: R = X = Et, S = Et_2O; 7: R = X = ~iBu, S = Et_2O; 8: R = Et, X = Cl, S = Et_2O). Crystal structures of 1, 2 and 7 demonstrate that the conformation of the eight-membered heterocycles containing aluminum is controlled by an unusual intramolecular C-H...O hydrogen bond. Et_2AlCl or ~iBu_3Al reacts with one equivalent of 2,2'-ethylidene-bis-(4,6-di-tert-butylphenol) (EDBP-H_2) or MDBP-H_2 in toluene giving a dimeric four coordinate compound [CLAL(#mu#-EDBP)]_2, 9 or [~iBuAl(#mu#-MDBP)]_2, 10. Some of these compounds have shown great catalytic activities toward the reaction of cyclopentadiene with methacrolein.