Bis(β-diketiminate) Rare-Earth-Metal Borohydrides: Syntheses, Structures, and Catalysis for the Polymerizations of l-Lactide, ε-Caprolactone, and Methyl Methacrylate

Abstract

Reaction of LnCl3 (Ln = Y, Yb) with 2 equiv of NaL2,6-ipr2Ph (L2,6-ipr2Ph = [(2,6-iPr2C6H3)NC(Me)CHC(Me)N(C6H5)]−) afforded the chlorides (L2,6-ipr2Ph)2YCl (1) and (L2,6-ipr2Ph)2YbCl (2). Crystal structure analysis revealed 2 to be the unsolvated monomer. Treatment of the chlorides 1 and 2 with NaBH4 in a 1/1 molar ratio in THF led to the preparation of the monoborohydrides (L2,6-ipr2Ph)2LnBH4 (Ln = Y (3), Yb (4)) in good yields. Reaction of LnCl3 (Ln = Y, Yb) with 2 equiv of NaL2-Me (L2-Me = [N(2-MeC6H4)C(Me)]2CH–) in THF, followed by treatment with 1 equiv of NaBH4, afforded the monoborohydrides (L2-Me)2LnBH4 (Ln = Y (5), Yb (6)). Complexes 3–6 were fully characterized, including X-ray crystal structure analyses. Complexes 3–6 are isostructural. The central metal in each complex is ligated by two β-diketiminate ligands and one η3-BH4– group in a distorted trigonal bipyramid. Complexes 3–6 were found to be highly active in the ring-opening polymerization of l-lactide (l-LA) and e-caprolactone (e-CL) to g...