Unusual bonding situations in Th(iv) and U(iv)-Al(iii) pnictogen complexes

To enhance our understanding of the electronic structure of early actinides, a synthetic methodology of using an Al(i) precursor, [(C₅Me₅)Al]₄, was applied to both thorium and uranium dipnictido complexes. The cleavage of the E-E bond in dipnictido actinide complexes, [(C₅Me₅)₂An(η ²-E₂R₂)], An = Th, U; E = N, P, As; R = Ph or 2,4,6-Me₃C₆H₂ (Mes), with 0.25 equivalents of [Al(C₅Me₅)]_4, yields the heterobimetallic complexes, [(C₅Me₅)₂An(µ ₂-ER)₂Al(C₅Me₅)]. In the case of An = U, E = N, the U(vi) bis(imido) complex, [(C₅Me₅)₂U(=NPh)₂], is reduced by [(C₅Me₅)Al]. Based on the solid-state structures and DFT calculations, including Nucleus Independent Chemical Shift (NICS), all six complexes show aromaticity within the An-E-Al-E moiety. For Th, only σ-aromaticity is observed, but both σ + π aromaticity is observed in the U complexes.