Trapping of Anionic Organic Radicals by (Tp^Me2)₂Ln (Ln = Sm, Eu)

Stoichiometric reaction of [Sm(TpMe2)2], 1, with a variety of reducible ketone- and quinone-type substrates gave thermally stable, isolable radical anions/ketyls in moderate to good yields. Thus reaction with benzophenone gave [Sm(TpMe2)2(OCPh2)], 2, with fluorenone [Sm(TpMe2)2(η1-OC13H8)], 3, and di-tert-butylparaquinone [Sm(TpMe2)2(η1-OC6H2(tBu)2O)], 4, each of which was structurally characterized. In the case of the less-hindered benzoquinone, an unimetallic semiquinone [Sm(TpMe2)2(OC6H4O)], 5, could be isolated, although it was unstable with respect to formation of the dimetallic complex [Sm(TpMe2)2]2(μ-OC6H4O), 6. Compound 6 was structurally characterized, as was its anthraquinone analogue [Sm(TpMe2)2]2(μ-OC14H8O), 7. When the analogous reaction was carried out between the less-reducing [Eu(TpMe2)2] and benzoquinone, only the europium analogue of the semiquinone 5, [Eu(TpMe2)2(OC6H4O)], 8, could be isolated. The use of the sterically hindered 3,5-di-tert-butyl-o-benzoquinone allowed isolation of [Sm(TpMe2)2(DTBSQ)], 9.