Anionic tris(cyclopentadienyl)actinide(IV) complexes

Abstract

Anionic complex salts, A+[M(cp)3(NCS)2]–(cp =η-C5H5), where A =[K(Crypt)](Crypt = Cryptofix-222) or NMe4 and M = U, and A = AsPh4 with M = U, Np, or Pu, have been prepared. Spectrophotometric and other evidence indicates trigonal-bipyramidal co- ordination for the metal atoms in the uranium complex anions, as in the known structure of the neutral complex [U(cp)3(NCS)(NCMe)]. The η-methylcyclopentadienyl analogue of the last complex is more difficult to obtain and dissociates more readily than the cp compound. Although evidence for the formation of uncharged [Np(cp)3(NCS)(NCMe)] in solution was obtained, the neutral neptunium complex could not be isolated and [Pu(cp)3(NCS)] reacts even less readily with methyl cyanide. A systematic investigation of the effects of the additional anion Y– in various solvents for the systems [U(cp)3XY]–, where X and/or Y = F–, OH–, CN–, NCBH3–, NCS–, and NCO–, shows that, in addition to steric factors, the specific distribution of the excess negative charge plays an important role. The first mixed anionic complex K[U(cp)3(OCN)(NCS)] was also obtained. Infrared, 1H n.m.r. (U compounds only), and near-i.r.–visible spectra are reported.