Uranium rhodium bonding in heterometallic complexes

The heterotetra- and bimetallic uranium(IV)–rhodium(I) complexes [UIVI2(μ-OArP-1κ1O,2κ1P)2RhI(μ-I)]2 (2) (ArPO− = 2-(diphenylphosphino)-6-tert-butyl-4-methylphenoxide) and UIVI(μ-I)(μ-OArP-1κ1O,2κ1P)3RhI (3) were prepared by treatment of UIVI(OArP-κ2O,P)3 (1) with rhodium(I) iodide olefin complexes. The reaction of 1 with the monodentate cyclooctene (coe) rhodium(I) precursor [(coe)2RhII]2 gives only the bimetallic complex [UIVRhI] 3, and with the diene [(cod)RhII]2 (5) (cod = 1,5-cyclooctadiene), mixtures of [UIVRhI]2 complex 2 and [UIVRhI] 3 along with (cod)RhIOArP-κ2O,P (4), a RhI side-product from the formation of 2. The complexes were characterised by single crystal X-ray diffraction, NMR and UV-vis-NIR spectroscopy, and electrochemistry. The UIV–RhI intermetallic distances in 2 (2.7601(5) Å) and 3 (2.7630(5) Å) are among the shortest between f-elements and transition metals reported to date. Despite almost identical U–Rh bond lengths in the solid state, in solution only weak, and very different interactions between the metal centres are found.