Pentadienyluranium borohydride complexes and their cyclopentadienyl analogues; crystal structures of (η-2,4-Me2C5H5)U(BH4)3 and (η-C5H5)U(BH4)3

Article abstract of DOI:10.1016/0022-328X(89)88023-4

Treatment of U(BH4)4 (I) with the potassium salt of the 2,4-dimethylpentadienyl anion (dmpd) afforded the pentadienyl complex (dmpd)U(BH4)3 (II), whereas the reaction of (dmpd)3U (VI) with TlBH4 gave (dmpd)2U(BH4)2 (IV).Complex VI reacted with KBH4 in the presence of 18-crown-6-ether to give the anionic uranium(III) compound <(dmpd)2U(BH4)2> (VII), and the corresponding cyclopentadienyl derivative (VIII) was obtained from the Na/Hg reduction of Cp2U(BH4)2 (V).The open pentadienyl ligand of these complexes was found to be less strongly bound to the metal centre than its cyclic counterpart in the corresponding cyclopentadienyl derivatives.The crystal structures of the pseudo-tetrahedral II and CpU(BH4)3 (III) complexes show that the U-C-(pentadienyl) bonds are longer than the U-C (cyclopentadienyl) bonds, and that there is a large degree of ionic character in the metal-pentadienyl bonding.