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, (E₂PR₂)^1– (E = S, Se; R = ^<i>i</i>Pr, ^<i>t</i>Bu), with thorium­(IV) and uranium­(IV) complexes. For the thorium dithiophosphinate complexes, reaction of ThCl₄(DME)₂ with 4 equiv of KS₂PR₂ (R = ^<i>i</i>Pr, ^<i>t</i>Bu) produced the homoleptic complexes, Th­(S₂P^<i>i</i>Pr₂)₄ (<b>1S-Th-</b>^{<i><b>i</b></i>}<b>Pr</b>) and Th­(S₂P^<i>t</i>Bu₂)₄ (<b>2S-Th-</b>^{<i><b>t</b></i>}<b>Bu</b>). The diselenophosphinate complexes were synthesized in a similar manner using KSe₂PR₂ to produce Th­(Se₂P^<i>i</i>Pr₂)₄ (<b>1Se-Th-</b>^{<i><b>i</b></i>}<b>Pr</b>) and Th­(Se₂P^<i>t</i>Bu₂)₄ (<b>2Se-Th-</b>^{<i><b>t</b></i>}<b>Bu</b>). U­(S₂P^<i>i</i>Pr₂)₄, <b>1S-U-</b>^{<i><b>i</b></i>}<b>Pr</b>, could be made directly from UCl₄ and 4 equiv of KS₂P^<i>i</i>Pr₂. With (Se₂P^<i>i</i>Pr₂)^1–, using UCl₄ and 3 or 4 equiv of KSe₂P^<i>i</i>Pr₂ yielded the monochloride product U­(Se₂P^<i>i</i>Pr₂)₃Cl (<b>3Se-U</b>^{<i><b>i</b></i><b>Pr</b>}<b>-Cl</b>), but using UI₄(1,4-dioxane)₂ produced the homoleptic U­(Se₂P^<i>i</i>Pr₂)₄ (<b>1Se-U-</b>^{<i><b>i</b></i>}<b>Pr</b>). Similarly, the reaction of UCl₄ with 4 equiv of KS₂P^<i>t</i>Bu₂ yielded U­(S₂P^<i>t</i>Bu₂)₄ (<b>2S-U-</b>^{<i><b>t</b></i>}<b>Bu</b>), whereas the reaction with KSe₂P^<i>t</i>Bu₂ resulted in the formation of U­(Se₂P^<i>t</i>Bu₂)₃Cl (<b>4Se-U</b>^{<b><i>t</i>Bu</b>}<b>-Cl</b>). Using UI₄(1,4-dioxane)₂ and 4 equiv of KSe₂P^<i>t</i>Bu₂ with UCl₄ in acetonitrile yielded U­(Se₂P^<i>t</i>Bu₂)₄ (<b>2Se-U-</b>^{<i><b>t</b></i>}<b>Bu</b>). Transmetalation reactions were investigated with complex <b>2Se-U-</b>^{<i><b>t</b></i>}<b>Bu</b> and various CuX (X = Br, I) salts to yield U­(Se₂P^<i>t</i>Bu₂)₃X (<b>6Se-U</b>^{<b><i>t</i>Bu</b>}<b>-Br</b> and <b>7Se-U</b>^{<b><i>t</i>Bu</b>}<b>-I</b>) and 0.25 equiv of [Cu­(Se₂P^<i>t</i>Bu₂)]₄ (<b>8Se-Cu-</b>^{<i><b>t</b></i>}<b>Bu</b>). Additionally, <b>2Se-U-</b>^{<i><b>t</b></i>}<b>Bu</b> underwent transmetalation reactions with Hg₂F₂ and ZnCl₂ to yield U­(Se₂P^<i>t</i>Bu₂)₃F (<b>6</b>) and U­(Se₂P^<i>t</i>Bu₂)₃Cl (<b>4Se-U</b>^{<b><i>t</i>Bu</b>}<b>-Cl</b>), respectively. The molecular structures were analyzed using ¹H, ¹³C, ³¹P, and ⁷⁷Se 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