INTERACTION OF ORGANIC CARBONYLS WITH STERICALLY CROWDED ARYLOXIDE COMPOUNDS OF ALUMINUM

The interaction of AlR(BHT)2 and AlR2(BHT)(OEt2) (R = Me, Et) with organic carbonyls O═C(X)R (X = H, Rʹ, OR, NR2) leads to the formation of the Lewis acid-base complexes AlR(BHT)2[O═C(X)R] and AlR2(BHT)[O═C(X)R], respectively. The aluminum-methyl13C NMR chemical shifts for the methyl aryloxide compounds AlMe(BHT)2[O═C(X)R] and AlMe2(BHT)[O═C(X)R] are found to be dependent primarily on the steric bulk of the substituents, X and R, on the carbonyl ligand. In contrast, the decrease in the carbonyl stretching frequency in the IR spectrum, and the downfield shift in the13C NMR spectrum for the carbonyl α-carbon of the carbonyl adducts, when compared to those of the “free” carbonyls, is dependent on the electron-donating ability of X. The molecular structures of AlMe(BHT)2[O═C(H)But] (1), AlMe2(BHT)(O═CPh2) (8), and AlMe(BHT)2[O═C(OMe)Ph] (17) have been determined by X-ray crystallography. The mode of coordination of the organic carbonyls to aluminum is discussed. Crystal data for 1: monoclinic, P21/n, a = 10.0765 (5) Å, b = 26.201 (2) Å, c = 14.0106 (4) Å, β = 103.638 (3)°, Z = 4, R = 0.0576, Rw = 0.0623. Crystal data for 8: orthorhombic, Pn21a, a = 19.133 (3) Å, b = 14.638 (2) Å, c = 10.022 (1) Å, Z = 4, R = 0.0552, Rw = 0.0550. Crystal data for 17: triclinic, P1, a = 9.394 (2) Å, b = 9.741 (3) Å, c = 23.091 (7) Å, α = 91.43 (2)°, β = 91.93 (2)°, γ = 116.41 (2)°, Z = 2, R = 0.0599, Rw = 0.0689. © 1990, American Chemical Society. All rights reserved.