Clear-cut lanthanide(III)/actinide(III) differentiation in coordination of pyrazine to tris(cyclopentadienyl) complexes of cerium and uranium, involving reversible UIII → UIV oxidation

In contrast to the [Ce(C5H4R)(3)] complexes (where R = tBu, SiMe3) which react with pyrazine to give the Lewis base adducts [Ce(C5H4R)(3)(pyz)] (where R = tBu 1, SiMe3 2), the uranium analogues are oxidized by the azine molecule to the dinuclear U-IV complexes [{U(C5H4R)(3)}(2)(mu-pyz)] (R = tBu 3, SiMe3 4). The U-N distances of approximately 2.32 Angstrom in the crystal structures of 3 and 4 are characteristic of U-IV-N bond lengths of terminally-coordinated amide groups. The formation constants of 1 and 3 in THF at 23 degreesC are 0.28(6) and 8(1) x 10(3), respectively, permitting the clear differentiation between the two metallocenes by means of the nitrogen ligand. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.