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

A series of substituted N , N ′-diarylhydrazines (ArNHNHAr), Ar = 3,5-(CH 3 )-C 6 H 3 ; -Ph; 4-Cl-C 6 H 4 ; 3,5-Cl-C 6 H 3 ; 3,5-(CF 3 )-C 6 H 3 , were reacted with Ce( iii )[N(SiMe 3 ) 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 Li 4 (Et 2 O) 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&z.dbd;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. A series of substituted N , N ′-diarylhydrazines (ArNHNHAr) were reacted with Ce( iii )[N(SiMe 3 ) 2 ] 3 and LiN(SiMe 3 ) 2 to form complexes of general formula Li 4 (OEt 2 ) 4 [Ce( iv )(ArNNAr) 4 ] where the spectroscopic and redox properties were affected by the ligand substitution.