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
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Abstract
The reactivities
of different 3-imino-functionalized indoles with
rare-earth-metal amides [(Me<sub>3</sub>Si)<sub>2</sub>N]<sub>3</sub>RE(μ-Cl)Li(THF)<sub>3</sub> 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-(<i>tert-</i>butylimino)indole with [(Me<sub>3</sub>Si)<sub>2</sub>N]<sub>3</sub>RE(μ-Cl)Li(THF)<sub>3</sub> produced tetranuclear rare-earth-metal complexes {[η<sup>1</sup>:(μ<sub>2</sub>-η<sup>1</sup>:η<sup>1</sup>):η<sup>1</sup>-3-(<i>t</i>BuNCH)C<sub>8</sub>H<sub>4</sub>N]RE<sub>2</sub>(μ<sub>2</sub>-Cl)<sub>2</sub>(THF)[N(SiMe<sub>3</sub>)<sub>2</sub>](η<sup>1</sup>:η<sup>1</sup>-[μ-η<sup>5</sup>:η<sup>2</sup><i>-</i>3-(<i>t</i>BuNCH)C<sub>8</sub>H<sub>5</sub>N]<sub>2</sub>Li)}<sub>2</sub> (RE = Ho (<b>1a</b>), Er (<b>1b</b>)), incorporating a unique indolyl-1,2-dianion through sp<sup>2</sup> C–H activation bonded with the central metal in η<sup>1</sup>:(μ<sub>2</sub>-η<sup>1</sup>:η<sup>1</sup>) mode. The reactions of 3-(phenylimino)indole with [(Me<sub>3</sub>Si)<sub>2</sub>N]<sub>3</sub>RE(μ-Cl)Li(THF)<sub>3</sub> afforded novel binuclear complexes formulated as {3-[PhNCH(CH<sub>2</sub>SiMe<sub>2</sub>)N(SiMe<sub>3</sub>)]C<sub>8</sub>H<sub>5</sub>NRE(THF)(μ<sub>2</sub>-Cl)Li(THF)<sub>2</sub>}<sub>2</sub> (RE = Y (<b>2a</b>), Sm (<b>2b</b>), Dy
(<b>2c</b>), Yb (<b>2d</b>)) through an unexpected sp<sup>3</sup> C–H bond activation with subsequent C–C bond
coupling reactions. Treatment of 3-(2-methylphenylimino)indole
or 3-(4-methylphenylimino)indole with [(Me<sub>3</sub>Si)<sub>2</sub>N]<sub>3</sub>Yb(μ-Cl)Li(THF)<sub>3</sub> generated
the corresponding dinuclear rare-earth-metal amido complexes {3-[(2-MePh)NCH(CH<sub>2</sub>SiMe<sub>2</sub>)N(SiMe<sub>3</sub>)]C<sub>8</sub>H<sub>5</sub>NYb(THF)(μ<sub>2</sub>-Cl)Li(THF)<sub>2</sub>}<sub>2</sub> (<b>3</b>) and {3-[(4-MePh)NCH(CH<sub>2</sub>SiMe<sub>2</sub>)N(SiMe<sub>3</sub>)]C<sub>8</sub>H<sub>5</sub>NYb(THF)(μ<sub>2</sub>-Cl)Li(THF)<sub>2</sub>}<sub>2</sub> (<b>4</b>), following the same pathway for the formation
of complexes <b>2a</b>–<b>d</b>. Treatment of 3-(4-<i>tert</i>-butylphenylimino)indole with [(Me<sub>3</sub>Si)<sub>2</sub>N]<sub>3</sub>RE(μ-Cl)Li(THF)<sub>3</sub> afforded new hexanuclear rare-earth-metal complexes {3-[(4-<sup><i>t</i></sup>Bu-Ph)NHCH(CH<sub>2</sub>SiMe<sub>2</sub>)N(SiMe<sub>3</sub>)]C<sub>8</sub>H<sub>5</sub>NREN(SiMe<sub>3</sub>)<sub>2</sub>}<sub>6</sub> (RE = Dy (<b>5a</b>), Ho
(<b>5b</b>), Er (<b>5c</b>)) via sp<sup>3</sup> C–H
bond activation followed by C–C bond coupling reactions. In
contrast, under the same conditions as those for the preparation of <b>5</b>, the reaction with the corresponding yttrium complex provided
the new heterohexayttrium complex {3-[(4-<i>t</i>Bu-Ph)NCH(CH<sub>2</sub>SiMe<sub>2</sub>)N(SiMe<sub>3</sub>)]C<sub>8</sub>H<sub>5</sub>NYN(SiMe<sub>3</sub>)<sub>2</sub>Li(THF)}<sub>6</sub> (<b>6</b>), having a 4-<i>t</i>Bu-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
