C–H Bond Activation by an Isolated Dinuclear U(III)/U(IV) Nitride

Synthetic studies of bimetallic uranium nitride complexes with the N(SiMe 3 ) 2 ligand have generated a new nitride complex of U(III), which is highly reactive toward C–H bonds and H 2 . Treatment of the previously reported U(IV)/U(IV) nitride complex [Na(DME) 3 ][((Me 3 Si) 2 N) 2 U(μ-N)(μ-κ 2: CN̵ –CH 2 SiMe 2 NSiMe 3 )U(N(SiMe 3 ) 2 ) 2 ] (DME = 1,2-dimethoxyethane), 1, with 2 equiv of HNEt 3 BPh 3 yielded the cationic U(IV)/U(IV) nitride complex, [{((Me 3 Si) 2 N) 2 U(THF)} 2 (μ-N)][BPh 4 ] (THF = tetrahydrofuran), 3, by successive protonolysis of one N(SiMe 3 ) 2 ligand and the uranium–methylene bond. Reduction of 3 with KC 8 afforded a rare example of a U(III) nitride, namely, the U(III)/U(IV) complex, [{((Me 3 Si) 2 N) 2 U(THF)} 2 (μ-N)], 4 . Complex 4 is highly reactive and undergoes 1,2-addition of the C–H bond of the N(SiMe 3 ) 2 ligand across the uranium–nitride moiety to give the U(III)/U(IV) imide cyclometalate complex, [((Me 3 Si) 2 N) 2 (THF)U(μ-NH)(μ-κ 2: C, N ̵–CH 2 SiMe 2 NSiMe 3 )U(N(SiMe 3 ) 2 ))(THF)], 5 . Complex 4 also reacts with toluene at −80 °C to yield an inverse sandwich imide complex arising from C–H bond activation of toluene, [{((Me 3 Si) 2 N) 2 U(THF)} 2 (μ-N)][{((Me 3 Si) 2 N) 3 U(μ-NH)U(N(SiMe 3 ) 2 )} 2 (C 7 H 8 )], 6 . Complex 4 effects the heterolytic cleavage of the C–H of phenylacetylene to yield the imide acetylide [{((Me 3 Si) 2 N) 2 U(THF)} 2 (μ-N)][((Me 3 Si) 2 N) 2 U(η 1 -CCPh)(μ 2 -NH)(μ 2 -η 2:η 1 -CCPh)U(N(SiMe 3 ) 2 ) 2 ], 7 . Complex 4 also reacts with H 2 to produce an imide hydride U(III)/U(IV) complex, [{((Me 3 Si) 2 N) 2 U(THF)} 2 (μ-NH)(μ-H)], 9 . These data demonstrate that nitride complexes of U(III) are accessible with amide ligands and show the high reactivity of molecular U(III) nitrides in C–H bond activation.