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

The reactions of R2AlX with one equivalent of 2,2'-methylene-bis-(4,6-di-te rt-butylphenol) (MDBP-H-2) or 2,2'-methylene-bis(4-methyl-6-tert-butylpheno l) (MMBP-H-2) in oxygenated solvent afford monomeric four-coordinated compo unds, XAl(MDBP)(S), 1-5 (1: R=Me, X=Br, S=Et2O; 2: R=Et, X=Cl, S=Et2O; 3. R =Me, X=Br, S=THF; 4. R=Et, X = Cl, S = THF; 5: R = X = Et, S = Et2O) or XAl (MMBP)(S), 6-8 (6. R = X = Et, S = Et2O; 7: R = X = Bu-i, S = Et2O; 8: R = Et, X = Cl, S = Et2O). Crystal structures of 1, 2 and 7 demonstrate that th e conformation of the eight-membered heterocycles containing aluminum is co ntrolled by an unusual intramolecular C-H ... O hydrogen bond. Et2AlCl or ( Bu3Al)-Bu-i 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 coord inate compound [CLAL(mu-EDBP](2), 9 or [(BuAl)-Bu-i(mu-MDBP)](2), 10. Some of these compounds have shown great catalytic activities toward the reactio n of cycloyentadiene with methacrolein. (C) 1999 Elsevier Science S.A. All rights reserved.