The interaction of the ytterbium bis(indenyl) complex (C 9 H 7 ) 2 Yb II (THF) 2 (1) with the 1,4 diazabutadiene 2 MeC 6 H 4 N=C(Me)-C(Me)=NC 6 H 4 Me 2 ( Me DAD) is accompa nied by the oxidation of the metal atom to the trivalent state and results in a paramagnetic compound of the metallocene type (C 9 H 7 ) 2 Yb III ( Me DAD -• ) (3) containing the radical anion of 1,4 diazabutadiene. The structure of the complex 3 was determined by X ray diffraction analysis. The reactions of the bis(indenyl) (1) and bis(fluorenyl) (C 13 H 9 ) 2 Yb II (THF) 2 (2) derivatives of divalent ytterbium with the 1,4 diazabutadiene PhN=C(Ph)-C(Ph)=NPh ( Ph DAD) (with the molar ratio of the reactants 1:2) proceed with a complete cleavage of the bonds Yb-C and the oxidation of the ytterbium atom to the trivalent state and result in a homoligand complex ( Ph DAD -• ) 3 Yb (6) containing three radical anion 1,4 diazadiene ligands. Complex 6 was also obtained by an exchange reaction of YbCl 3 with Ph DAD -• K + (1 : 3) in THF. Complex 6 was characterized by X ray diffraction analysis.Disubstituted 1,4 diazabutadienes RN=C(R´)-C(R´)=NR (DAD) owing to the variety of their coordi nation and redox properties turned out to be a promising type of ligand environment for rare earth metals, and their use allowed the preparation of new complexes pos sessing both new structure types and unique reactivity. 1 Due to the "redox activity" and also a low energy of the π* orbitals 2 of diazadiene ligands, their coupling with metals of the lanthanoid series, which have several stable oxidation states (particularly with ytterbium), 3 may give rise to the development of new prospective models for the study of the intramolecular process of the metalligand electron transfer. In addition, studies of recently obtained homo and heteroleptic ytterbium 1,4 diazabuta diene complexes has led to the discovery of a number of challenging processes such as thermally induced redox isomerism, 4 reversible intramolecular metal-ligand elec tron transfer triggered by the change in the nature of the solvent (coordinating or non coordinating). 5 The investi gations of ytterbocene reactions with diimines have demonstrated the possibility of steric control on a redox reaction. 6 In order to get a more in depth understanding of the possibility of modification of redox properties of ytterbocenes by varying the degree of the steric load of the coordi national sphere of the ytterbium atom, it seems worthwhile to study the reactions of this type of com pounds differing in both the volume of carbocyclic ligands coordinated at the metal atom and the nature of the metal-ligand bond (namely, the tendency of these ligands for haptotropic rearrangements). In addition, of particu lar interest is the study of the influence of the volume and nature of substituents at both the nitrogen atoms and the imine carbon atoms in the molecule of 1,4 diazadiene on the direction of the ytterbocene -diazabutadiene reac tion. In the present work the investigation of reactions of the ytterbium bis(indenyl) (C...

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