Uranium(VI) Sulfilimine Complexes: A New Class of Nitrogen Analogues of the Uranyl Ion

The compound tetraphenylphosphonium tetrachlorooxo-S,S-diphenylsulfiliminatouranium, [Ph4P][UOCl4(NSPh2)],
has been prepared in high yield from [Ph4P][UOCl5] and [Ph2SNSiMe3]. An X-ray structure of this compound
shows that the uranium atom has a pseudooctahedral geometry with oxygen and nitrogen atoms in trans positions.
The structure of the analogous phosphoriminato complex [Ph4P][UOCl4(NPPh3)] has been determined for
comparison. Derivatization of the sulfide group shows that only a limited range of functionalization confers stability
toward reduction. The emission spectrum of the first electronic excited state reveals a greatly reduced energy
compared with that of the uranyl ion. This red shift in the transition is consistent with the weakening of the U−N
bond relative to the U−O bond.