π-bonding in four-coordinate aluminum aryloxide compounds

Article abstract of DOI:10.1021/ja00164a017

The interaction of AlMe₃ with the substituted phenols 2,6-di-tert-butyl-4-methylphenol (BHT-H), 2,6-diisopropylphenol (DIP-H), and 2,4,6-trimethylphenol (MesOH) in the presence of pyridine (py) or 3,5-dimethylpyridine (3,5-Me₂py) leads to the formation of mono, bis, and tris aryloxide compounds. The molecular structures of AlMe₂(BHT)(py) (3a), AlMe(OMes)₂(3,5-Me₂py) (8b), and Al(DIP)₃(py) (7a) have been determined by X-ray crystallography. The Al-O distances are shorter and Al-O-C angles larger than usually found for aluminum alkoxides. The presence of a π-type interaction between the aryloxide ligands and the four-coordinate aluminum centers is proposed to account for the structural results. Compound 3a: monoclinic P2₁/n, a = 10.193 (7) A, b = 17.989 (10) A, c = 12.249 (11) A, β = 96.44 (6)°, Z = 4, R = 0.076, R(w) = 0.078. Compound 8b: monoclinic P2₁/n, a = 11.767 (2) A, b = 10.232 (2) A, c = 21.562 (5) A, β = 105.43 (2)°, Z = 4, R = 0.076, R(w) = 0.091. Compound 7a: monoclinic P2₁/n, a = 13.032 (2) A, b = 21.308 (3) A, c = 14.605 (2) A, β = 107.99 (1), Z = 4, R = 0.068, R(w) = 0.068.