Dithio- and Diselenophosphinate Thorium(IV) and Uranium(IV)
Complexes: Molecular and Electronic Structures, Spectroscopy, and
Transmetalation Reactivity
We
report a comparison of the molecular and electronic structures of
dithio- and diselenophosphinate, (E<sub>2</sub>PR<sub>2</sub>)<sup>1–</sup> (E = S, Se; R = <sup><i>i</i></sup>Pr, <sup><i>t</i></sup>Bu), with thorium(IV) and uranium(IV) complexes.
For the thorium dithiophosphinate complexes, reaction of ThCl<sub>4</sub>(DME)<sub>2</sub> with 4 equiv of KS<sub>2</sub>PR<sub>2</sub> (R = <sup><i>i</i></sup>Pr, <sup><i>t</i></sup>Bu) produced the homoleptic complexes, Th(S<sub>2</sub>P<sup><i>i</i></sup>Pr<sub>2</sub>)<sub>4</sub> (<b>1S-Th-</b><sup><i><b>i</b></i></sup><b>Pr</b>) and Th(S<sub>2</sub>P<sup><i>t</i></sup>Bu<sub>2</sub>)<sub>4</sub> (<b>2S-Th-</b><sup><i><b>t</b></i></sup><b>Bu</b>). The diselenophosphinate complexes were synthesized in a similar
manner using KSe<sub>2</sub>PR<sub>2</sub> to produce Th(Se<sub>2</sub>P<sup><i>i</i></sup>Pr<sub>2</sub>)<sub>4</sub> (<b>1Se-Th-</b><sup><i><b>i</b></i></sup><b>Pr</b>) and Th(Se<sub>2</sub>P<sup><i>t</i></sup>Bu<sub>2</sub>)<sub>4</sub> (<b>2Se-Th-</b><sup><i><b>t</b></i></sup><b>Bu</b>). U(S<sub>2</sub>P<sup><i>i</i></sup>Pr<sub>2</sub>)<sub>4</sub>, <b>1S-U-</b><sup><i><b>i</b></i></sup><b>Pr</b>, could be made directly from
UCl<sub>4</sub> and 4 equiv of KS<sub>2</sub>P<sup><i>i</i></sup>Pr<sub>2</sub>. With (Se<sub>2</sub>P<sup><i>i</i></sup>Pr<sub>2</sub>)<sup>1–</sup>, using UCl<sub>4</sub> and
3 or 4 equiv of KSe<sub>2</sub>P<sup><i>i</i></sup>Pr<sub>2</sub> yielded the monochloride product U(Se<sub>2</sub>P<sup><i>i</i></sup>Pr<sub>2</sub>)<sub>3</sub>Cl (<b>3Se-U</b><sup><i><b>i</b></i><b>Pr</b></sup><b>-Cl</b>), but using UI<sub>4</sub>(1,4-dioxane)<sub>2</sub> produced the
homoleptic U(Se<sub>2</sub>P<sup><i>i</i></sup>Pr<sub>2</sub>)<sub>4</sub> (<b>1Se-U-</b><sup><i><b>i</b></i></sup><b>Pr</b>). Similarly, the reaction of UCl<sub>4</sub> with 4 equiv of KS<sub>2</sub>P<sup><i>t</i></sup>Bu<sub>2</sub> yielded U(S<sub>2</sub>P<sup><i>t</i></sup>Bu<sub>2</sub>)<sub>4</sub> (<b>2S-U-</b><sup><i><b>t</b></i></sup><b>Bu</b>), whereas the reaction with KSe<sub>2</sub>P<sup><i>t</i></sup>Bu<sub>2</sub> resulted in the
formation of U(Se<sub>2</sub>P<sup><i>t</i></sup>Bu<sub>2</sub>)<sub>3</sub>Cl (<b>4Se-U</b><sup><b><i>t</i>Bu</b></sup><b>-Cl</b>). Using UI<sub>4</sub>(1,4-dioxane)<sub>2</sub> and 4 equiv of KSe<sub>2</sub>P<sup><i>t</i></sup>Bu<sub>2</sub> with UCl<sub>4</sub> in acetonitrile yielded U(Se<sub>2</sub>P<sup><i>t</i></sup>Bu<sub>2</sub>)<sub>4</sub> (<b>2Se-U-</b><sup><i><b>t</b></i></sup><b>Bu</b>). Transmetalation reactions were investigated with complex <b>2Se-U-</b><sup><i><b>t</b></i></sup><b>Bu</b> and various CuX (X = Br, I) salts to yield U(Se<sub>2</sub>P<sup><i>t</i></sup>Bu<sub>2</sub>)<sub>3</sub>X (<b>6Se-U</b><sup><b><i>t</i>Bu</b></sup><b>-Br</b> and <b>7Se-U</b><sup><b><i>t</i>Bu</b></sup><b>-I</b>) and 0.25 equiv of [Cu(Se<sub>2</sub>P<sup><i>t</i></sup>Bu<sub>2</sub>)]<sub>4</sub> (<b>8Se-Cu-</b><sup><i><b>t</b></i></sup><b>Bu</b>). Additionally, <b>2Se-U-</b><sup><i><b>t</b></i></sup><b>Bu</b> underwent
transmetalation reactions with Hg<sub>2</sub>F<sub>2</sub> and ZnCl<sub>2</sub> to yield U(Se<sub>2</sub>P<sup><i>t</i></sup>Bu<sub>2</sub>)<sub>3</sub>F (<b>6</b>) and U(Se<sub>2</sub>P<sup><i>t</i></sup>Bu<sub>2</sub>)<sub>3</sub>Cl (<b>4Se-U</b><sup><b><i>t</i>Bu</b></sup><b>-Cl</b>), respectively.
The molecular structures were analyzed using <sup>1</sup>H, <sup>13</sup>C, <sup>31</sup>P, and <sup>77</sup>Se NMR and IR spectroscopy and
structurally characterized using X-ray crystallography. Using the
QTAIM approach, the electronic structure of all homoleptic complexes
was probed, showing slightly more covalent bonding character in actinide–selenium
bonds over actinide–sulfur bonds