SYNTHESIS AND REACTIVITY OF HYDROTRIS(PYRAZOLYL)BORATE SIGMA-HYDROCARBYL URANIUM(IV) COMPLEXES

Stable sigma-hydrocarbyl uranium (IV) compounds could not be obtained by simple metathesis reactions of [UCl(3)L*(TKF)] (L* = HB(3,5-Me(2)pz)(3)) with LiMe, LiC6H5, or LiCH2C6H5 . THF. The reactions with LiMe resulted in uncharacterizable mixtures of products and the reactions with LiCH2C6H5 . THF or LiC6H5 yielded a known reduced uranium compound, {UCl(2)L*}(x). Decomposition pathways could be prevented by using a second ancillary ligand such as Cp or by introducing a bulky substituent on the aromatic ring of the benzyl or phenyl. Reactions of [UCl(2)CpL*] with LiMe gave [UCl(2-x)CpMe(x)L*] (x = 1 (1) or 2 (2)) depending of the stoichiometric ratio of the reagents and the reactions of [UCl(3)L*(THF)] with Li-2-CH(2)C(6)H(4)NMe(2) or Li-2-C(6)H(4)CH(2)NMe(2) yielded the compounds [UCl2(2-CH(2)C(6)H(4)NMe(2))L*] (3) and [UCl2(2-C(6)H(4)CH(2)NMe(2))L*] (4), respectively. Compounds 3 and 4 are fluxional in solution at room temperature, but static spectra were obtained at low temperature. The observed dynamic behaviour can be explained by breaking and making the U-N coordinate bond of the chelating (2-CH(2)C(6)H(4)NMe(2)) or (2-C(6)H(4)CH(2)NMe(2)).