Abstract
The tetravalent uranium complexes with bridging ligands, (MeC/sub 5/H/sub 4/)/sub 2/(..mu..-NR)/sub 2/ have been prepared by the valence conproportionation reaction of (MeC/sub 5/H/sub 4/)/sub 3/U/times/thf and (MeC/sub 5/H/sub 4/)/sub 3/UNR. X-ray crystallographic study of R = Ph and SiMe/sub 3/ shows that the NPh group asymmetrically bridges the two uranium fragments, whereas the NSiMe/sub 3/ group symmetrically bridges the two uranium fragments. Crystals of (MeC/sub 5/H/sub 4/)/sub 4/U/sub 2/(NPh)/sub 2/ are monoclinic, P2/sub 1//n, with a = 14.738 (3) /Angstrom/, b = 9.933 (2) /Angstrom/, c = 10.612 (2) /Angstrom/, ..beta.. = 102.11 (2)/degrees/ at 23/degrees/C. For Z = 2 (dimers) the calculated density is 2.13 g/cm/sup 3/. The structure was refined by full-matrix least-squares to a conventional R factor of 0.029 (1600 data, F/sup 2/ > 2sigma(F/sup 2/)). Crystals of (MeC/sub 5/H/sub 4/)/sub 4/U/sub 2/(NSiMe/sub 3/)/sub 2/ also are monoclinic, P2/sub 1//n, with a = 15.761 (6) /Angstrom/, b = 9.389 (4) /Angstrom/, c = 11.052 (4) /Angstrom/, ..beta.. = 101.36 (3)/degrees/ at 23/degrees/C. For Z = 2 (dimers) the calculated density is 2.00 g/cm/sup 3/. The structure was refined by full-matrix least-squares to a conventional R factor of 0.023 (2544 data, F/sup 2/ > 2sigma(F/sup 2/)). Both complexes are dimers in which the two (MeC/sub 5/H/sub 4/)/sub 2/U fragments are bridged by the organoimide group so that an inversion center is located in the center of the U/sub 2/N/sub 2/ ring. The bridging U-N distances are 2.156 (8) and 2.315 (8) /Angstrom/ in the NPh complex and 2.217 (4) and 2.230 (4) /Angstrom/ in the NSiMe/sub 3/ complex. 22 references, 3 figures, 5 tables.