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, (eta(2)-(Ph2PNPr)-Pr-i)(4)U (1), (eta(2)-(i)Pr(2)PNMes)(4)U (2), (eta(2)-(Ph2PNPr)-Pr-i)(3)UCl (3), and (eta(2)-(i)Pr(2)PNMes)(3)UI (4), were easily accessed via addition of the appropriate stoichiometric equivalents of [(Ph2PNPr)-Pr-i]K or [(i)Pr(2)PNMes]K to UCl4 or UI4(dioxane)(2). Although the phosphinoamide ligands in 1 and 4 have been shown to coordinate to U in an eta(2)-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((Ph2PNPr)-Pr-i)(3)U[eta(2)-(Ph2PNPr)-Pr-i] (5), ICo((i)Pr(2)PNMes)(3)U[eta(2)-((i)Pr(2)PNMes)] (6), ICo-((Ph2PNPr)-Pr-i)(3)UI (7), and ICo((i)Pr(2)PNMes)(3)UI (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) angstrom). 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.