One-Electron Reduction of Aromatic Ketones by Low-Valent Lanthanides. Isolation, Structural Characterization, and Reactivity of Lanthanide Ketyl Complexes

TLDR: In this article, the isolation, structural characterization, and reactivity of a series of lanthanide ketyl complexes, which are generated by reactions of benzophenone and fluorenone with several different types of reducing agents including Ln(OAr)2(L)x (Ar = C6H2-tBu2-2,6-Me-4), (C5Me5)2Ln(THF)2 (Ln = Sm, L = THF, x = 3; 1b: Ln = Yb, L

Abstract: In this paper we report on the isolation, structural characterization, and reactivity of a series of lanthanide ketyl complexes, which are generated by reactions of benzophenone and fluorenone with several different types of lanthanide reducing agents including Ln(OAr)2(L)x (Ar = C6H2-tBu2-2,6-Me-4; 1a: Ln = Sm, L = THF, x = 3; 1b: Ln = Yb, L = THF, x = 3; 1c: Ln = Sm, L = HMPA, x = 2; 1d: Ln = Yb, L = HMPA, x = 2), (C5Me5)2Ln(THF)2 (Ln = Sm, Yb), (C5Me5)Sm(OAr)(HMPA)2, Sm(N(SiMe3)2)2(THF)2, and Ln/HMPA (Ln = Sm, Yb) (HMPA = hexamethylphosphoric triamide). Reactions of 1a−d with 1 equiv of fluorenone in THF afforded the corresponding ketyl complexes Ln(OAr)2(ketyl)(L)2 (3a−d) in 85−90% isolated yields. Hydrolysis of 3a (Ln = Sm, L = THF) gave the corresponding pinacol-coupling product, 1,2-bis(biphenyl-2,2‘-diyl)ethane-1,2-diol (4), while air oxidation of 3a yielded fluorenone almost quantitatively. Reaction of 3a with 1 equiv of 1a followed by hydrolysis afforded fluorenol quantitatively. When 3a was dis...