Rare-Earth-Metal Complexes
Supported by New Chiral
Tetra-Azane Chelating Ligands: Synthesis, Characterization, and Catalytic
Properties for Intramolecular Asymmetric Hydroamination
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Abstract
A number of new chiral tetra-azane proligands (1<i>R</i>,2<i>R</i>)-<i>N</i>,<i>N</i>′-bis(<i>o</i>-arylamino-benzylidene)-1,2-diaminocyclohexane
((1<i>R</i>,2<i>R</i>)-[(ArHN)C<sub>6</sub>H<sub>4</sub>CHN]<sub>2</sub>C<sub>6</sub>H<sub>10</sub>, Ar =
2,6-Me<sub>2</sub>C<sub>6</sub>H<sub>3</sub> (<b>L</b><sup><b>1</b></sup>H<sub>2</sub>), 2,6-Et<sub>2</sub>C<sub>6</sub>H<sub>3</sub> (<b>L</b><sup><b>2</b></sup>H<sub>2</sub>), 2,6-<sup><i>i</i></sup>Pr<sub>2</sub>C<sub>6</sub>H<sub>3</sub> (<b>L</b><sup><b>3</b></sup>H<sub>2</sub>)) have been synthesized
via a nucleophilic displacement of the two fluorine atoms in (<i>o</i>-C<sub>6</sub>H<sub>4</sub>FCHN)<sub>2</sub>C<sub>6</sub>H<sub>10</sub> with the lithium salt of the corresponding
aniline derivative. Their rare-earth-metal complexes <b>L</b><sup><b>1</b></sup>ScCl<sub>2</sub>Li(THF)<sub>3</sub> (<b>1</b>), <b>L</b><sup><b>1</b></sup>YCl<sub>2</sub>Li(THF)<sub>3</sub> (<b>2</b>), <b>L</b><sup><b>2</b></sup>YCl<sub>2</sub>Li(THF)<sub>3</sub> (<b>3</b>), and <b>L</b><sup><b>3</b></sup>YCl<sub>2</sub>Li(THF)<sub>2</sub> (<b>4</b>) were synthesized in good yields via the salt metathesis
of MCl<sub>3</sub> (M = Sc, Y) with the dilithium salts of the ligands <b>L</b><sup><b>1</b></sup>Li<sub>2</sub>(THF)<sub>4</sub>, <b>L</b><sup><b>2</b></sup>Li<sub>2</sub>(THF),<sub>4</sub>, and <b>L</b><sup><b>3</b></sup>Li<sub>2</sub>(THF)<sub>4</sub>, respectively. Further more, the two diethylamido complexes <b>L</b><sup><b>1</b></sup>Y(NEt<sub>2</sub>)ClLi(THF)<sub>3</sub> (<b>5</b>) and <b>L</b><sup><b>3</b></sup>Y(NEt<sub>2</sub>)ClLi(THF)<sub>2</sub> (<b>6</b>) were also
synthesized from reactions of the corresponding chloride complexes <b>2</b> and <b>4</b> with diethylamidolithium. The new proligands <b>L</b><sup><b>1</b></sup>H<sub>2</sub>–<b>L</b><sup><b>3</b></sup>H<sub>2</sub> and their rare-earth-metal
complexes <b>1</b>–<b>6</b> have been characterized
by elemental analyses and <sup>1</sup>H and <sup>13</sup>C NMR spectroscopy.
The structures of complexes <b>1</b>, <b>2</b>, and <b>4</b> have been further confirmed by single-crystal X-ray diffraction
analysis. The molecular structural analysis reveals that the metal
centers in complexes <b>1</b>, <b>2</b>, and <b>4</b> acquire a distorted-octahedral coordination environment in their
solid-state structures by sharing the chloride with a LiCl(THF)<sub><i>n</i></sub> moiety. After in situ treatment with <sup><i>n</i></sup>BuLi or Me<sub>3</sub>SiCH<sub>2</sub>Li,
complexes <b>1</b>–<b>4</b> show reasonable catalytic
activity and good enantioselectivity (up to 90%) for intramolecular
asymmetric hydroamination reactions of terminal aminoalkenes. The
amido complexes <b>5</b> and <b>6</b> can catalyze the
intramolecular hydroamination reaction directly and show catalytic
activities and enantioselectivities similar to those of the in situ
formed alkyl complexes
