Synthesis, Structure, and Reactivity of the Sterically Crowded Complex (C 5 Me 4 SiMe 3 ) 3 U

The unusual chemistry obtainable from sterically crowded (C 5 R 5 ) 3 M complexes has been explored with M = U and (C 5 Me 4 SiMe 3 ) 1– , a ligand that has independently provided unexpected uranium chemistry. (C 5 Me 4 SiMe 3 ) 2 UMe 2 ( 1 ), is reduced by potassium to generate the “ate” salt (C 5 Me 4 SiMe 3 ) 2 UMe 2 K ( 2 ), which reacts with [HNEt 3 ][BPh 4 ] to yield the cationic species [(C 5 Me 4 SiMe 3 ) 2 U][BPh 4 ] ( 3 ). KC 5 Me 4 SiMe 3 reacts with 3 in benzene to form (C 5 Me 4 SiMe 3 ) 3 U, ( 4 ). The structure of 4 shows that the displacement of the methyl groups from the cyclopentadienyl ring planes, a useful indicator of steric crowding, is the largest ever observed in a (C 5 R 5 ) 3 M complex. The reactivity of 4 is consistent with this structural indicator in that it engages in THF ring opening to form (C 5 Me 4 SiMe 3 ) 2 UO[(CH 2 ) 4 (C 5 Me 4 SiMe 3 )](THF).