Reinvestigation of the reaction of tert-butyllithium with uranium tetrachloride: formation of catalytically active uranium(III) hydride complexes

The reaction of UCl/sub 4/ with t-C/sub 4/H/sub 9/Li in alkane solvents has been reinvestigated in detail by quantitative collection and identification of gaseous products and by spectral, analytical, and chemical characterization of the solid uranium products. Treatment of UCl/sub 4/ with 4 equiv of t-C/sub 4/H/sub 9/Li generates 1.5 to 1.8 equiv of 2-methylpropane and 2-methylpropene in a 2.5-3 to 1 ratio and a solid U(III) hydride product which readily dissolves in tetrahydrofuran (THF). As much as 1.7 equiv of the starting alkyllithium reagent can be recovered unreacted in this reaction, and hence the primary features of the reaction can be reproduced by using only 2 equiv of t-C/sub 4/H/sub 9/Li. Reaction of 1 equiv of t-C/sub 4/H/sub 9/Li with UCl/sub 4/ forms a U(III) product free of hydride. The reaction of n-C/sub 4/H/sub 9/Li with UCl/sub 4/ is similar. Detailed analysis of alkane/alkene ratios of gaseous products suggests that these systems abstract hydrogen from the alkane solvent possibly through a low-valent uranium center. The U(III) hydride product of these reactions is catalytically active in alkyne and alkane hydrogenation reactions conducted under mild conditions.