Tris(boratabenzene) Lanthanum Complexes: Synthesis,
Structure, and Reactivity
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Abstract
A series of tris(boratabenzene) lanthanum
complexes were synthesized
and structurally characterized. Salt elimination of anhydrous LaCl<sub>3</sub> with Li[C<sub>5</sub>H<sub>5</sub>BR] (R = H, NEt<sub>2</sub>) provided tris(boratabenzene) lanthanum complexes [C<sub>5</sub>H<sub>5</sub>BH]<sub>3</sub>LaLiCl (<b>1</b>) and [C<sub>5</sub>H<sub>5</sub>BNEt<sub>2</sub>]<sub>3</sub>LaLiCl(THF)
(<b>2</b>) in high yields. Hydroboration of 1-hexene or 3-hexyne
with <b>1</b> gave the alkyl- or alkenyl-functionalized boratabenzene
lanthanum complexes, [C<sub>5</sub>H<sub>5</sub>B(CH<sub>2</sub>)<sub>5</sub>CH<sub>3</sub>]<sub>3</sub>LaLiCl(THF) (<b>3</b>) and [C<sub>5</sub>H<sub>5</sub>BC(C<sub>2</sub>H<sub>5</sub>)CH(C<sub>2</sub>H<sub>5</sub>)]<sub>3</sub>LaLiCl(THF) (<b>4</b>), in good yields. Hydroboration of <i>N</i>,<i>N</i>′-diisopropylcarbodiimide with <b>1</b> gave the monohydroboration
product [C<sub>5</sub>H<sub>5</sub>BN(<sup><i>i</i></sup>Pr)CHN(<sup><i>i</i></sup>Pr)][C<sub>5</sub>H<sub>5</sub>BH]<sub>2</sub>La (<b>5</b>) due to the steric
bulk of the [C<sub>5</sub>H<sub>5</sub>BN(<sup><i>i</i></sup>Pr)CHN(<sup><i>i</i></sup>Pr)]<sup>−</sup> ligand. Complex <b>5</b> can undergo further hydroboration
with 3-hexyne or dehydrogenative coupling with phenyl acetylene to
afford [C<sub>5</sub>H<sub>5</sub>BN(<sup><i>i</i></sup>Pr)CHN(<sup><i>i</i></sup>Pr)][C<sub>5</sub>H<sub>5</sub>BC(C<sub>2</sub>H<sub>5</sub>)CH(C<sub>2</sub>H<sub>5</sub>)]<sub>2</sub>La (<b>6</b>) or [C<sub>5</sub>H<sub>5</sub>BN(<sup><i>i</i></sup>Pr)CHN(<sup><i>i</i></sup>Pr)][C<sub>5</sub>H<sub>5</sub>BCCPh)]<sub>2</sub>La (<b>7</b>)
