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

Abstract

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 (ArNNAr). 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.