Synthesis of a heterobimetallic actinide nitride and an analysis of its bonding

Reaction of [K(DME)][Th{N(R)(SiMe(2)CH(2))}(2)(NR(2))] (R = SiMe(3)) with 1 equiv. of [U(NR(2))(3)(NH(2))] (1) in THF, in the presence of 18-crown-6, results in formation of a bridged uranium–thorium nitride complex, [K(18-crown-6)(THF)(2)][(NR(2))(3)U(IV)(μ-N)Th(IV)(NR(2))(3)] (2), which can be isolated in 48% yield after work-up. Complex 2 is the first isolable molecular mixed-actinide nitride complex. Also formed in the reaction is the methylene-bridged mixed-actinide nitride, [K(18-crown-6)][K(18-crown-6)(Et(2)O)(2)][(NR(2))(2)U(μ-N)(μ–κ(2)-C,N–CH(2)SiMe(2)NR)Th(NR(2))(2)](2) (3), which can be isolated in 34% yield after work-up. Complex 3 is likely generated by deprotonation of a methyl group in 2 by [NR(2)](−), yielding the new μ-CH(2) moiety and HNR(2). Reaction of 2 with 0.5 equiv. of I(2) results in formation of a U(V)/Th(IV) bridged nitride, [(NR(2))(3)U(V)(μ-N)Th(IV)(NR(2))(3)] (4), which can be isolated in 42% yield after work-up. The electronic structure of 4 was analyzed with EPR spectroscopy, SQUID magnetometry, and NIR-visible spectroscopy. This analysis demonstrated that the energies of 5f orbitals of 4 are largely determined by the strong ligand field exerted by the nitride ligand.