Preparation and reactions of base-free bis (1,2,4-tri-tert-butylcyclopentadienyl) uranium methylimide, CP′2U=NMe, and related compounds

The uranium metallocenes [eta 5-1,3-(Me3E)(2)C5H3](2) UMe2 (E = C, Si) react with NH3 to give the dimers {[eta 5-1,3-Me3E)(2)C5H3](2)U}2(mu-NH)(2) (E = C(1), Si (2)) but with p-toluidine to give the monomeric diamides [eta(5)-1,3-(Me3E)(2)C5H3](2)U(NH-p-tolyl)(2) (E=C (3), Si (4)) do not eliminate p-toluidine but sublime intact at 140 degrees C in a vacuum. The uranium metallocene [eta 5-1,2,4-(Me3C)(3)C5H2](2)UMe2 reacts with the RNH2 to yield [eta(5)-1,2,4-(Me3C)(3)C5H2](2)U(NHR)(2) (R = Me (8), PhCH2 (9), p-tolyl (10)), which are isolated as crystalline solids. In benzene solution these diamides are in equilibrium with [eta(5)-1,2,4-(Me3C)(3)C5H2](2)U = NR2, which may be isolated pure when R is Me (11) or p-tolyl (12), and the primary amine. The monomeric imide (eta(5)-1,2,4-(Me3C)(3)C5H2](2)U = NMe (11) reacts with R'C CR' to yield the cycloaddition products [eta(5)-1,2,4-(Me3C)(3)C5H2](2)U - [N(Me)C(R')] (R' = Me (15), Ph (16), which react with excess MeNH2 to regenerate the diamide [eta 5-1,2,4-(Me3C)(3)C5H2](2)U(NHMe)(2) (8) and MeN = C(R')CH(R'). The methylimide, [eta(5)-1,2,4-(Me3C)(3)C5H2](2)U = NMe (11), does not react with Me3SiX reagents; a model is proposed that rationalises this reactivity pattern.