Preparation and Reactions of Base-Free Bis(1,2,4-tri-tert-butylcyclopentadienyl)uranium Methylimide, Cp‘2UNMe, and Related Compounds

The uranium metallocenes [ η 5 -1,3-(Me 3 E) 2 C 5 H 3 ] 2 UMe 2 (E = C, Si) react with NH 3 to give the dimers {[ η 5 -1,3-(Me 3 E) 2 C 5 H 3 ] 2 U} 2 ( μ -NH) 2 (E = C ( 1 ), Si ( 2 )) but with p -toluidine to give the monomeric diamides [ η 5 -1,3-(Me 3 E) 2 C 5 H 3 ] 2 U(NH- p -tolyl) 2 (E = C ( 3 ), Si ( 4 )). The diamides [ η 5 -1,3-(Me 3 E) 2 C 5 H 3 ] 2 U(NH- p -tolyl) 2 (E = C ( 3 ), Si ( 4 )) do not eliminate p -toluidine but sublime intact at 140 °C in a vacuum. The uranium metallocene [ η 5 -1,2,4-(Me 3 C) 3 C 5 H 2 ] 2 UMe 2 reacts with RNH 2 to yield [ η 5 -1,2,4-(Me 3 C) 3 C 5 H 2 ] 2 U(NHR) 2 (R = Me ( 8 ), PhCH 2 ( 9 ), p -tolyl ( 10 )), which are isolated as crystalline solids. In benzene solution these diamides are in equilibrium with [ η 5 -1,2,4-(Me 3 C) 3 C 5 H 2 ] 2 U NR, which may be isolated pure when R is Me ( 11 ) or p -tolyl ( 12 ), and the primary amine. The monomeric imide [ η 5 -1,2,4-(Me 3 C) 3 C 5 H 2 ] 2 U NMe ( 11 ) reacts with R‘C⋮CR‘ to yield the cycloaddition products [ η 5 -1,2,4-(Me 3 C) 3 C 5 H 2 ] 2 U[N(Me)C(R‘) C(R‘)] (R‘ = Me ( 15 ), Ph ( 16 )), which react with excess MeNH 2 to regenerate the diamide [ η 5 -1,2,4-(Me 3 C) 3 C 5 H 2 ] 2 U(NHMe) 2 ( 8 ) and MeN C(R‘)CH(R‘). The methylimide, [ η 5 -1,2,4-(Me 3 C) 3 C 5 H 2 ] 2 U NMe ( 11 ), does not react with Me 3 SiX reagents; a model is proposed that rationalizes this reactivity pattern.