CRYSTAL-STRUCTURES OF [(ME(3)SI)(2)N](4)U-2[MU-N(H)(MESITYL)](2) AND [(ME(3)SI)(2)N](4)U-2[MU-N(P-TOLYL)](2) - COMPOUNDS WITH ASYMMETRICALLY BRIDGING PRIMARY AMIDE AND IMIDE GROUPS

The trivalent uranium amide, [(Me(3)Si)(2)N]U-4(2)[mu-N(H)(mesityl)](2 ), was prepared by the acid-base reaction between [(Me(3)Si)(2)N]U-3 a nd mesitylamine. The pKa's of (Me(3)Si)(2)NH and mesitylamine are not particularly helpful in predicting the outcome of the proton transfer reaction; this is probably due to the change in pKa upon coordination to the uranium center. X-ray crystallographic analysis (-75 degrees C) of the compound; monoclinic P2(1)/n, a=16.997(1) Angstrom, b=11.854(1 ) Angstrom, c=15.121 (2) Angstrom, beta=99.10(1)degrees, V=3008 Angstr om(3), Z=2; shows that the mesitylamide (the amide hydrogen atom was l ocated but not refined) asymmetrically bridges the two [(Me(3)Si)(2)N] U-2 centers with U-N distances of 2.453(3) Angstrom and 2.646(3) Angst rom and a U-N-U angle of 102.9(1)degrees. The tetravalent uranium orga noimide, [(Me(3)Si)(2)N]U-4(2)[mu-N(p-tolyl)](2) was prepared in the r eaction of [(Me(3)Si)(2)N]3UCl and LiN(H)(p-tolyl), a reaction which i s thought to involve a proton transfer step. X-ray crystallographic an alysis (-118 degrees) of the compound; triclinic, p-1 a=9.792(1) Angst rom, b=12.212(1) Angstrom, c=14.580(3) alpha=62.00(1)degrees, beta=65. 86(1)degrees, gamma=80.80(1)degrees, V=1403 Angstrom(3), Z=1; shows th at the p-tolylimide asymmetrically bridges the two [(Me(3)Si)(2)N]U-2 centers with U-N distances of 2.378(3) Angstrom and 2.172(2) Angstrom and a U-N-U angle of 105.8(1)degrees. The asymmetry is ascribed to ele ctronic (hybridization) effects. Magnetic susceptibility studies from 5-280 K on both compounds show no magnetic interaction between the U . .. U centers.