Synthesis and Structure of a Terminal Uranium Nitride Complex

The terminal uranium nitride linkage is a fundamental target in the study of f-orbital participation in metal-ligand multiple bonding but has previously eluded characterization in an isolable molecule. Here, we report the preparation of the terminal uranium(V) nitride complex [UN(Tren TIPS )][Na(12-crown-4) 2 ] {in which Tren TIPS = [N(CH 2 CH 2 NSiPr i 3 ) 3 ] 3− and Pr i = CH(CH 3 ) 2 } by reaction of the uranium(III) complex [U(Tren TIPS )] with sodium azide followed by abstraction and encapsulation of the sodium cation by the polydentate crown ether 12-crown-4. Single-crystal x-ray diffraction reveals a uranium-terminal nitride bond length of 1.825(15) angstroms (where 15 is the standard uncertainty). The structural assignment is supported by means of 15 N-isotopic labeling, electronic absorption spectroscopy, magnetometry, electronic structure calculations, elemental analyses, and liberation of ammonia after treatment with water.