Cyanide metallocenes of trivalent f-elements

Addition of (NBu4CN)-Bu-n to (C5Me5)(2)UI(py), (C5Me5)(2)CeI, or (C5Me5)(2)M(OTf) (M = U, Ce) in acetonitrile led to the precipitation of the neutral monocyanide species [(C5Me5)(2)M(mu-CN)](n) [M = U (1), Ce (2)], which likely have an oligomeric structure, as shown by the trimeric cyanide-bridged complex [(C5Me5)(2)Ce(mu-CN)((CNBu)-Bu-t)](3) (3) obtained by addition of excess (BuNC)-Bu-t into a suspension of 2 in acetonitrile. The structure of the U(III,IV) mixed valence compound [{(C5Me5)(2)U}(2)(mu-CN){(mu-CN)(2)Na(thf)}(2)](infinity) (4), which crystallized from a thf solution of (C5Me5)(2)UI(py) in the presence of excess NaCN, reveals a unique example of an f-element-(mu-CN)-M interaction (M = main group or d transition metal). The anionic polycyanides [(C5Me5)(2)M(CN)(3)][(NBu4)-Bu-n](2) [M = U (5), Ce (6)] were synthesized by treatment of 1 and 2 with 2 equiv or an excess of (NBu4CN)-Bu-n in acetonitrile; they were also prepared in a one-pot procedure by stepwise addition of 1 equiv of KCN and 2 equiv of (NBu4CN)-Bu-n to the parent iodides in acetonitrile. The bent metallocenes 5 and 6 are unique low-valent molecular polycyanide compounds of an f-element that have been structurally identified, while 5 is the first fully characterized actinide(III) cyanide. Comparison of the crystal structures of 5 and 6 shows that the M-C(C5Me5) and M-C(CN) distances are 0.02-0.03 angstrom shorter for M = U than for M = Ce, while the ionic radius of uranium(III) is 0.02 angstrom larger than that of cerium(III).