Abstract
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.
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