Accessing relatively electron poor cerium(iv) hydrazido complexes by lithium cation promoted ligand reduction

A series of substituted N,N'-diarylhydrazines (ArNHNHAr), Ar = 3,5-(CH3)-C6H3; -Ph; 4-Cl-C6H4; 3,5-Cl-C6H3; 3,5-(CF3)-C6H3, were reacted with Ce(iii)[N(SiMe3)2]3 and lithiated bases to explore the use of Ce(iii) as a reductant and to evaluate the impact of the ligand substitution on the electronic structure at the cerium metal centre of the resulting complexes. The N,N'-diarylhydrazido ligands were coordinated by the Li(+) cation and then reduced by a Ce(iii) cation to form Li4(Et2O)4[Ce(IV)(ArNNAr)4] complexes in all cases. Stabilization of the resulting Ce(iv) product depended on the substituents on the N,N'-diarylhydrazido ligands. Isolable cerium products formed only with electron withdrawing substituents on the N,N'-diarylhydrazido rings, whereas electron donating substituents resulted in intractable mixtures of Ce(iii) products and N,N'-bis(aryl)diazenes (ArN[double bond, length as m-dash]NAr). The presence of electron withdrawing substituents at the N,N'-diarylhydrazido ligands formed relatively electron poor Ce(iv) complexes, which were probed by UV-Vis spectroscopy, cyclic voltammetry, and DFT calculations. The Lewis acid promoted reduction of hydrazobenzene derivatives by Ce(iii) was thus demonstrated to be a successful method to access electron poor cerium(iv) complexes.