A series of eight scorpionate ligands (Ar) 2 CHR (1− 4) were synthesized and coordinated to aluminum to produce Al(CH 2 CH 3 )((Ar) 2 CHR) (5−8), where R = CH 2 OCH 3 (1 or 5), CH 2 N(CH 3 ) 2 (2 or 6), imidazole (3 or 7), or N-methylimidazole (4 or 8), and Ar = 2,4-dimethylphenol (a) or 2-tert-butyl-4methylphenol (b). The bisphenol compounds were generated using a Friedel−Crafts alkylation reaction starting with commercially available reagents. The scorpionate species were subsequently combined with triethylaluminum in order to probe the coordination geometries of 1−4. The resulting complexes 5−8 displayed distorted tetrahedral structures with the bisphenolate ligands acting as tridentate donors. The only exception was 5a, which formed phenolate bridged dimers in the solid state. Additionally, complexes 5−8 were found to be active catalysts for the ring-opening polymerization of ε-caprolactone. The aluminum alkyl species affected this transformation both with and without the use of an alcohol co-catalyst, but higher activities and cleaner activations were seen when 1 equiv of iPrOH was employed. The less sterically hindered complexes with more weakly bound hemilabile "tails" showed the highest activities, with nearly 100% conversion after 1 h at 50 °C, and a catalyst loading of 1 mol %.

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