Facile synthesis of zwitterionic organoaluminum complexes containing formally dianionic homoscorpionate ligands

Abstract

A series of zwitterionic aluminum complexes of the type AlX[(2‐O‐3,5‐tBu2C6H2)3PZ] (AlX [O3PZ]; X = Cl, Me, Et, and iBu; Z = H, Me) containing C3‐symmetric, formally dianionic, facially tridentate ligands [O3PZ]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‐tBu2C6H2)3P (H3[O3P]) or [(2‐HO‐3,5‐tBu2C6H2)3p.m.e](OTf) ({H3[O3PMe]}OTf) in THF at 25°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 ε‐caprolactone is assessed.