Facile synthesis of zwitterionic organoaluminum complexes containing formally dianionic homoscorpionate ligands

A series of zwitterionic aluminum complexes of the type AlX[(2-O-3,5-tBu(2)C(6)H(2))(3)PZ] (AlX [O(3)PZ]; X = Cl, Me, Et, and iBu; Z = H, Me) containing C-3-symmetric, formally dianionic, facially tridentate ligands [O(3)PZ](2-) were prepared and structurally characterized. Although serendipitous, these complexes can be readily synthesized by partial protonolysis of AlX3 with equal molar (2-HO-3,5-tBu(2)C(6)H(2))(3)P (H-3[O3P]) or [(2-HO-3,5-tBu(2)C(6)H(2))(3)p.m.e](OTf) ({H-3[O3PMe]}OTf) in THF at 25 degrees C or elevated temperatures. Alcoholysis of AlMe[O3PMe] (2) with an excess amount of MeOH in refluxing toluene generates AlOMe[O3PMe] (10). Salt metathesis of AlCl[O3PMe] (6) with nBuM (M = Li, MgCl) and NaOR (R = tBu, Ph) in ethereal solutions affords AlnBu[O3PMe] (9) and AlOR[O3PMe] (R = tBu (11), Ph (12)), respectively. Reactivity of 10, 11, and 12 with respect to catalytic ring-opening polymerization of epsilon-caprolactone is assessed.