Tris(phosphinoamide)-Supported Uranium–Cobalt Heterobimetallic Complexes Featuring Co → U Dative Interactions

A series of tris- and tetrakis­(phosphinoamide) U/Co complexes has been synthesized. The uranium precursors, (η²-Ph₂PNⁱPr)₄U (1), (η²-ⁱPr₂PNMes)₄U (2), (η²-Ph₂PNⁱPr)₃UCl (3), and (η²-ⁱPr₂PNMes)₃UI (4), were easily accessed via addition of the appropriate stoichiometric equivalents of [Ph₂PNⁱPr]K or [ⁱPr₂PNMes]K to UCl₄ or UI₄(dioxane)₂. Although the phosphinoamide ligands in 1 and 4 have been shown to coordinate to U in an η²-fashion in the solid state, the phosphines are sufficiently labile in solution to coordinate cobalt upon addition of CoI₂, generating the heterobimetallic Co/U complexes ICo­(Ph₂PNⁱPr)₃U­[η²-Ph₂PNⁱPr] (5), ICo­(ⁱPr₂PNMes)₃U­[η²-(ⁱPr₂PNMes)] (6), ICo­(Ph₂PNⁱPr)₃UI (7), and ICo­(ⁱPr₂PNMes)₃UI (8). Structural characterization of complexes 5 and 7 reveals reasonably short Co–U interatomic distances, with 7 exhibiting the shortest transition metal–uranium distance ever reported (2.874(3) Å). Complexes 7 and 8 were studied by cyclic voltammetry to examine the influence of the metal–metal interaction on the redox properties compared with both monometallic Co and heterobimetallic Co/Zr complexes. Theoretical studies are used to further elucidate the nature of the transition metal–actinide interaction.