Reactivity of 3‑Imino-Functionalized Indoles with Rare-Earth-Metal Amides: Unexpected Substituent Effects on C–H Activation Pathways and Assembly of Rare-Earth-Metal Complexes

The reactivities
of different 3-imino-functionalized indoles with
rare-earth-metal amides [(Me3Si)2N]3RE­(μ-Cl)­Li­(THF)3 were studied to reveal unexpected
substituent effects on C–H bond activation pathways, leading
to the formation of unusual rare-earth-metal complexes. The reactions
of 3-(tert-butylimino)­indole with [(Me3Si)2N]3RE­(μ-Cl)­Li­(THF)3 produced tetranuclear rare-earth-metal complexes {[η1:(μ2-η1:η1):η1-3-(tBuNCH)­C8H4N]­RE2­(μ2-Cl)2(THF)­[N­(SiMe3)2]­(η1:η1-[μ-η5:η2-3-(tBuNCH)­C8H5N]2Li)}2 (RE = Ho (1a), Er (1b)), incorporating a unique indolyl-1,2-dianion through sp2 C–H activation bonded with the central metal in η1:(μ2-η1:η1) mode. The reactions of 3-(phenylimino)­indole with [(Me3Si)2N]3RE­(μ-Cl)­Li­(THF)3 afforded novel binuclear complexes formulated as {3-[PhNCH­(CH2SiMe2)­N­(SiMe3)]­C8H5NRE­(THF)­(μ2-Cl)­Li­(THF)2}2 (RE = Y (2a), Sm (2b), Dy
(2c), Yb (2d)) through an unexpected sp3 C–H bond activation with subsequent C–C bond
coupling reactions. Treatment of 3-(2-methylphenylimino)­indole
or 3-(4-methylphenylimino)­indole with [(Me3Si)2N]3­Yb­(μ-Cl)­Li­(THF)3 generated
the corresponding dinuclear rare-earth-metal amido complexes {3-[(2-MePh)­NCH­(CH2SiMe2)­N­(SiMe3)]­C8H5NYb­(THF)­(μ2-Cl)­Li­(THF)2}2 (3) and {3-[(4-MePh)­NCH­(CH2SiMe2)­N­(SiMe3)]­C8H5NYb­(THF)­(μ2-Cl)­Li­(THF)2}2 (4), following the same pathway for the formation
of complexes 2a–d. Treatment of 3-(4-tert-butylphenylimino)­indole with [(Me3Si)2N]3RE­(μ-Cl)­Li­(THF)3 afforded new hexanuclear rare-earth-metal complexes {3-[(4-tBu-Ph)­NHCH­(CH2SiMe2)­N­(SiMe3)]­C8H5NREN­(SiMe3)2}6 (RE = Dy (5a), Ho
(5b), Er (5c)) via sp3 C–H
bond activation followed by C–C bond coupling reactions. In
contrast, under the same conditions as those for the preparation of 5, the reaction with the corresponding yttrium complex provided
the new heterohexayttrium complex {3-[(4-tBu-Ph)­NCH­(CH2SiMe2)­N­(SiMe3)]­C8H5NYN­(SiMe3)2­Li­(THF)}6 (6), having a 4-tBu-anilido
moiety. All of these complexes were fully characterized by elemental
analysis, spectroscopic methods, and X-ray structure analysis. Plausible
pathways for the formation of these different rare-earth-metal complexes
were proposed.