Cyanide Metallocenes of Trivalent f-Elements.

Addition of NnBu4CN to (C5Me5)2UI(py), (C5Me5)2CeI, or (C5Me5)2M(OTf) (M U, Ce) in acetonitrile led to the precipitation of the neutral monocyanide species (C5Me5)2M(-CN)nM U (1), Ce (2), which likely have an oligomeric structure, as shown by the trimeric cyanide-bridged complex (C5Me5)2Ce(-CN)(CNtBu)3(3) obtained by addition of excess tBuNC into a suspension of 2in acetonitrile. The structure of the U(III,IV) mixed valence compound (C5Me5)2U2(-CN)(-CN)2Na(thf)2∞(4), which crystallized from a thf solution of (C5Me5)2UI(py) in the presence of excess NaCN, reveals a unique example of an f-element−(-CN)−M interaction (M main group or d transition metal). The anionic polycyanides (C5Me5)2M(CN)3NnBu42M U (5), Ce (6) were synthesized by treatment of 1and 2with 2 equiv or an excess of NnBu4CN in acetonitrile; they were also prepared in a one-pot procedure by stepwise addition of 1 equiv of KCN and 2 equiv of NnBu4CN to the parent iodides in acetonitrile. The bent metallocenes 5and 6are unique low-valent molecular polycyanide compounds of an f-element that have been structurally identified, while 5is the first fully characterized actinide(III) cyanide. Comparison of the crystal structures of 5and 6shows that the M−C(C5Me5) and M−C(CN) distances are 0.02−0.03 Å shorter for M U than for M Ce, while the ionic radius of uranium(III) is 0.02 Å larger than that of cerium(III). [ABSTRACT FROM AUTHOR]