Synthesis and Reactions of a Redox-Active α‑Diimine Aluminum Complex

The
reaction of the ene-diamine LH2 (L = [ArNC­(Me)­C­(Me)­NAr]2–, Ar = 2,6-iPr2C6H3) with AlMe3 and AlEt3 yielded
the aluminum dimethyl complex (LH)­AlMe2 (1) and the radical (L•)­AlEt2 (2; L• = [ArNC­(Me)­C­(Me)­NAr]•–), respectively. Treatment of 2 with O2 and
TEMPO (2,2,6,6-tetramethylpiperidin-1-oxyl) led to hydrogen abstraction
from the methyl group at the ligand backbone to give the diamagnetic
species (L*)­AlEt2 (3; L* = [ArNC­(Me)­C­(CH2)­NAr]−) and (L*)­Al­(TEMPO)­(Et) (4). In contrast, the reaction of 2 with iodine resulted
in the iodination of the Al–C bonds and yielded the radical
(L•)­AlI2 (5). Reaction of 2 with BCl3 led to electron transfer between the
α-diimine radicals with the formation of the aluminum cation
[(L0)­AlCl2]+[AlCl4]− (6; L0 = ArNC­(Me)­(Me)­CNAr)
and the diazaborole LBCl (7). The structures of compounds 2, 3, and 7 have been determined
by X-ray single-crystal diffraction, and the paramagnetic species 2 has been characterized by EPR measurements.