Sterically encumbered aluminum aryloxide complexes

This work was conducted as part of a broad-based effort to determine the factors that affect cation formation for organometallic aluminum complexes. Previous studies have shown that the cationic complexes [R(2)Al(NH(2)(t)Bu)(2)]X result from the combination of R(2)AlX and excess NH(2)(t)Bu when X = Br and I. In the present study the effect of replacing one alkyl group with the relatively bulky aryloxide (2,6-di-tert-butyl phenoxide = Ph*O) to yield complexes of formula [Me(Ph*O)AlX](2) (X = Cl (1), Br (2)) was examined. With excess NH(2)(t)Bu only the adduct species formed, Me(Ph*O)AlX(NH(2)(t)Bu) (where X = Cl (3)), Br (4)). In using R(2)AlI a different type of reaction occurs and only Ph*OAlMe(2)(NH(2)(t)Bu) (5) and [NH(3)(t)Bu]I are obtained. Of related interest, the compound Me(2)(Ph*O)Al(THF) (6) is also reported. The presence of 4 as an adduct species indicates that the inductive effect of the aryloxide prevents cation formation where X = Br, in contrast to the complexes which possess only alkyl. All of the compounds were characterized by mp, H-1 NMR, IR, elemental analyses, and in some cases, X-ray crystallography. X-ray data: (1) monoclinic, P2(1)/n, a = 10.604(1), b = 20.776(4), c = 14.752(1) Angstrom, beta = 92.450(1)degrees, V = 3247.1(7) Angstrom(3), Z = 4, with 3245 reflections with F > 4.0 sigma F, R = 0.0436; (3) orthorhombic, Pna2(1), a = 16.879(2), b = 12.315(2), c = 10.442(1) Angstrom, V = 2170.5(5) Angstrom(3), Z = 4, With 1270 reflections with F > 4.0 sigma F, R = 0.0477; (5) orthorhombic, Pna2(1), a = 17.111(3), b = 12.375(1), c = 10.380(1) Angstrom, V = 2197.7(5) Angstrom(3), Z = 4, with 1226 reflections with F > 4.0 sigma F, R = 0.0538.