Chloro and Alkyl Rare-Earth
Complexes Supported by <i>ansa</i>-Bis(amidinate) Ligands with a Rigid <i>o</i>‑Phenylene Linker. Ligand Steric
Bulk: A Means of Stabilization or Destabilization?
- Publication date
- Publisher
Abstract
<i>ansa</i>-Bis(amidinate) ligands with a rigid <i>o</i>-phenylene linker, C<sub>6</sub>H<sub>4</sub>-1,2-{NC(<i>t</i>Bu)N(2,6-R<sub>2</sub>C<sub>6</sub>H<sub>3</sub>)H}<sub>2</sub> (R = Me (<b>1</b>), <i>i</i>Pr (<b>2</b>)), were successfully employed for the synthesis of rare-earth chloro
and alkyl species. The reaction of dilithium derivatives of <b>1</b> and <b>2</b> with LnCl<sub>3</sub> (Ln = Y, Lu) afforded
the monomeric bis(amidinate) chloro lanthanide complexes [C<sub>6</sub>H<sub>4</sub>-1,2-{NC(<i>t</i>Bu)N(2,6-R<sub>2</sub>C<sub>6</sub>H<sub>3</sub>)}<sub>2</sub>]Y(THF)(μ-Cl)<sub>2</sub>Li(THF)<sub>2</sub> (R = Me (<b>3</b>), <i>i</i>Pr
(<b>5</b>)) and [C<sub>6</sub>H<sub>4</sub>-1,2-{NC(<i>t</i>Bu)N(2,6-Me<sub>2</sub>C<sub>6</sub>H<sub>3</sub>)}<sub>2</sub>]LuCl(THF)<sub>2</sub> (<b>4</b>). Bis(amidinate) ligands
in complexes <b>3</b> and <b>4</b> are coordinated to
the metal atoms in a tetradentate fashion, while the bulkier ligand
in <b>5</b> is tridentate. The alkane elimination reactions
of <b>1</b> and <b>2</b> with equimolar amounts of (Me<sub>3</sub>SiCH<sub>2</sub>)<sub>3</sub>Ln(THF)<sub>2</sub> (Ln = Y,
Lu) allowed us to obtain the monoalkyl complexes [C<sub>6</sub>H<sub>4</sub>-1,2-{NC(<i>t</i>Bu)N(2,6-R<sub>2</sub>C<sub>6</sub>H<sub>3</sub>)}<sub>2</sub>]Ln(CH<sub>2</sub>SiMe<sub>3</sub>)(THF)<sub><i>n</i></sub> (Ln = Y, R = Me, <i>n</i> = 1
(<b>6</b>); Ln = Lu, R = Me, <i>n</i> = 1 (<b>7</b>); Ln = Y, R = <i>i</i>Pr, <i>n</i> = 2 (<b>8</b>)). The kinetics of thermal decomposition of complexes <b>6</b>–<b>8</b> were measured, and for <b>6</b> the activation energy was obtained from the temperature dependence
of the rate constants (<i>E</i><sub>a</sub> = 67.0 ±
1.3 kJ/mol). Complexes <b>6</b> and <b>7</b> turned out
to be inert toward H<sub>2</sub> and PhSiH<sub>3</sub>. Surprisingly,
complex <b>8</b> was inert toward H<sub>2</sub> and PhSiH<sub>3</sub> but rapidly cleaved C–O bonds of DME. The reaction
resulted in the formation of the methoxy complex {[C<sub>6</sub>H<sub>4</sub>-1,2-{NC(<i>t</i>Bu)N(2,6-<i>i</i>Pr<sub>2</sub>C<sub>6</sub>H<sub>3</sub>)}<sub>2</sub>]Y(μ<sub>2</sub>-OMe)]}<sub>2</sub>(μ<sub>2</sub>-DME) (<b>9</b>) and
methyl vinyl ether
