In Pursuit of Homoleptic
Actinide Alkyl Complexes
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Abstract
This Forum Article describes the pursuit of isolable
homoleptic
actinide alkyl complexes, starting with the pioneering work of Gilman
during the Manhattan project. The initial reports in this area suggested
that homoleptic uranium alkyls were too unstable to be isolated, but
Wilkinson demonstrated that tractable uranium alkyls could be generated
by purposeful “ate” complex formation, which serves
to saturate the uranium coordination sphere and provide the complexes
with greater kinetic stability. More recently, we reported the solid-state
molecular structures of several homoleptic uranium alkyl complexes,
including [Li(THF)<sub>4</sub>][U(CH<sub>2</sub><sup>t</sup>Bu)<sub>5</sub>], [Li(TMEDA)]<sub>2</sub>[UMe<sub>6</sub>], [K(THF)]<sub>3</sub>[K(THF)<sub>2</sub>][U(CH<sub>2</sub>Ph)<sub>6</sub>]<sub>2</sub>, and [Li(THF)<sub>4</sub>][U(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>6</sub>], by employing Wilkinson’s strategy. Herein,
we describe our attempts to extend this chemistry to thorium. The
treatment of ThCl<sub>4</sub>(DME)<sub>2</sub> with 5 equiv of LiCH<sub>2</sub><sup>t</sup>Bu or LiCH<sub>2</sub>SiMe<sub>3</sub> at −25
°C in THF affords [Th(CH<sub>2</sub><sup>t</sup>Bu)<sub>5</sub>] (<b>1</b>) and [Li(DME)<sub>2</sub>][Th(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>5</sub> (<b>2</b>), respectively, in moderate
yields. Similarly, the treatment of ThCl<sub>4</sub>(DME)<sub>2</sub> with 6 equiv of K(CH<sub>2</sub>Ph) produces [K(THF)]<sub>2</sub>[Th(CH<sub>2</sub>Ph)<sub>6</sub>] (<b>3</b>), in good yield.
Complexes <b>1</b>–<b>3</b> have been fully characterized,
while the structures of <b>1</b> and <b>3</b> were confirmed
by X-ray crystallography. Additionally, the electronic properties
of <b>1</b> and <b>3</b> were explored by density functional
theory
