New homo- and heteroleptic derivatives of trivalent ytterbium containing radical anion 1,4-diazadiene ligands. Synthesis, properties, and crystal structures of the complexes (C9H7)2Yb[2-MeC6H4NC(Me)C(Me)NC6H4Me-2] and [PhNC(Ph)C(Ph)NPh]3Yb

Abstract

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...

Sterically Governed Redox Reactions. One-Electron Oxidation of Ytterbocenes by Diazabutadienes: Formation of Radical-Anionic Diazabutadiene vs Covalently Bonded Imino–Amido Ligand

“…7a These reactions can follow different paths and result in metal atom oxidation, 5cÀf CÀC bond formation, 8 CÀH bond activation, 7a and YbÀCp bond cleavage. 9 The reductive capacity of ytterbocenes in their reactions with diazabutadienes was found to be sterically tunable from one-to two-electron reduction. 6 The less sterically crowded ytterbocene (C 5 MeH 4 ) 2 Yb(THF) 2 acts as a one-electron reductant, and the reaction affords a bis-(cyclopentadienyl)ytterbium(III) derivative containing a DAD radical anion (C 5 MeH 4 ) 2 Yb III (DAD •À ), while the compounds Cp* 2 Yb(THF) 2 (Cp* = C 5 Me 5 , C 5 Me 4 H), containing more sterically demanding cyclopentadienyl ligands, reduce the DAD molecule to a dianionic state due to oxidation of Yb II to Yb III and oxidative cleavage of the YbÀCp* bond.…”

“…8b The transition to a DAD ligand containing a methyl substituent at the ortho position of the phenyl rings, 2-MeC 6 H 4 NdC(Me)C(Me)dNC 6 H 4 Me-2, once again changed dramatically the reaction result: one-electron transfer from the metal to the DAD ligand was observed, and the complex (C 9 H 7 ) 2 Yb III -(DAD •À ) was isolated. 9 The recent finding of the possibility of governing metalÀligand electron transfer processes in the reactions of ytterbocenes with iminopyridynes (Ipy) due to the introduction of various substituents into the 6-position of the pyridyl ring of the Ipy ligand inspired us to go further in the studies of the steric effect in redox reactions. 7b In order to address this issue, we investigated the reactions of a series of ytterbocenes of variable steric hindrance (C 5 Me n H 5Àn ) 2 Yb(THF) x (n = 1, 4, 5; x = 1,2) with diazabutadienes 2-RC 6 H 4 NdC(Me)C-(Me)dNC 6 H 4 R-2 (R = H, Me) having modest steric demand.…”

“…The application of redox-noninnocent 1,4-diazabutadiene ligands (DAD) in reductive organolanthanide chemistry (especially in that of ytterbium, for which two rather stable Yb II and Yb III oxidation states are characteristic) had considerable impact on the development of this area and revealed new challenging phenomena such as solvent-mediated redox tranformations − , and temperature-induced redox isomerism . Redox reactions of ytterbocenes with 1,4-diazabutadienes turned out to be extremely diverse and dependent on a number of factors .…”

“…Redox reactions of ytterbocenes with 1,4-diazabutadienes turned out to be extremely diverse and dependent on a number of factors . These reactions can follow different paths and result in metal atom oxidation, − C–C bond formation, C–H bond activation, and Yb–Cp bond cleavage . The reductive capacity of ytterbocenes in their reactions with diazabutadienes was found to be sterically tunable from one- to two-electron reduction .…”

“…In this case, the phenyl substituents of the 1,4-diazabutadiene ligand are involved in the metal–ligand bonding . The transition to a DAD ligand containing a methyl substituent at the ortho position of the phenyl rings, 2-MeC 6 H 4 NC(Me)C(Me)NC 6 H 4 Me-2, once again changed dramatically the reaction result: one-electron transfer from the metal to the DAD ligand was observed, and the complex (C 9 H 7 ) 2 Yb III (DAD •– ) was isolated …”