SYNTHESIS AND SPECTROSCOPIC INVESTIGATIONS OF ALKYLALUMINUM DERIVATIVES OF 2-ALLYL-6-METHYLPHENOXIDE AND 2-NAPHTHOXIDE - CRYSTAL-STRUCTURE OF [ME2AL(MU-2-ALLYL-6-METHYLPHENOXIDE)]2

The reaction of trialkylaluminum, R3A1 (R = Me, Et, or i-Bu), with phenols such as 2-allyl-6-methylphenol and 2-naphthol yields quantitatively dialkylaluminum phenoxide, R2AlOR’ (R = Me, 1a: Et, 1b; i-Bu, 1c; OR’ = 2-allyl-6-methylphenoxide; and R = Et, 2b; i-Bu, 2c; OR’ = 2-naphthoxide) and the corresponding alkane RH. The resulting phenoxides have been characterized by1H and13C NMR spectroscopy. The single-crystal X-ray study of 1a established that it crystallizes in the monoclinic cell system, space group P21/n, with cell constants a = 9.862 (2) Å, b = 9.682 (1) Å, c = 13.417 (2) Å, β = 97.98 (1)°, and Z = 2 (dimers); final R = 5.62%, Rw = 4.87%, based on 1021 observed reflections; Fo ≥ 2.5σ(F). The molecular unit is a dimer, bridged by two 2-allyl-6-methylphenoxide ligands, leading to the formation of a planar four-membered Al2O2 ring. Attempts to disrupt the Al–O bridge bonds and form stable adducts with the bases diethyl ether, tetrahydrofuran, and methyl benzoate failed, but 4-picoline gives a 1:1 complex. In solution, at low temperature, la exists as two conformera that undergo rapid exchange on the NMR time scale at room temperature. The observed behavior is consistent with the rotational process in which the syn and anti conformera interconvert by rotation of the bridging phenoxide group with an activation energy of 9.7 ± 2 kcal mol-1. © 1990, American Chemical Society. All rights reserved.