Delocalization and Valence Tautomerism in Vanadium Tris(iminosemiquinone) Complexes

Abstract

To survey the noninnocence of bis(arylimino) acenaphthene (BIAN) ligands (L) in complexes with early metals, the homoleptic vanadium complex, [V(L)3 ] (1), and its monocation, [V(L)3 ]PF6 (2), were synthesized. These complexes were found to have a very rich electronic behavior, whereby 1 displays strong electronic delocalization and 2 can be observed in unprecedented valence tautomeric forms. The oxidation states of the metal and ligand components in these complexes were assigned by using spectroscopic, crystallographic, and magnetic analyses. Complex 1 was identified as [V(IV) (L(red) )(L(.) )2 ] (L(red) =N,N'-bis(3,5-dimethylphenylamido)acenaphthylene; L(.) =N,N'-bis(3,5-dimethylphenylimino)acenaphthenesemiquinonate). Complex 2 was determined to be [V(V) (L(red) )(L(.) )2 ](+) at T<150 K and [V(IV) (L(.) )3 ](+) at T>150 K. Cyclic voltammetry experiments reveal six quasi-reversible processes, thus indicating the potential of this metal-ligand combination in catalysis or materials applications.

A New Class of Lanthanide Complexes with Three Ligand Centered Radicals: NMR Evaluation of Ligand Field Energy Splitting and Magnetic Coupling

“…The 1 H NMR spectrum of Y(Ph‐BIAN) 3 (Figure S1) changes only slightly with temperature, in analogy to the description of a related vanadium complex featuring highly similar ligands . This behavior disagrees with a pure doublet or quartet state, for which a T −1 dependence of the chemical shifts is expected.…”

“…To the best of our knowledge, the reaction of this ligand with lanthanide halogenides has so far not been reported in a 3:1 stoichiometry . Notably, similar vanadium complexes with a related ligand have been described previously …”

“…The 1 HNMR spectrum of Y(Ph-BIAN) 3 (FigureS1) changes only slightly with temperature, in analogy to the description of ar elated vanadium complex featuring highly similar ligands. [14] This behavior disagrees with ap ure doublet or quartet state, for which a T À1 dependence of the chemical shifts is expected. However,t he observed temperature dependence is in agreement with ad oublet ground state and quartet state close in energy.U pon increase of the temperature,t he Boltzmann occupancyoft he quartet state increases, for whichhigher chemical shifts occur resulting from the larger number of unpaired electrons.S imultaneously,t he T À1 dependence of the chemical shifts of both the ground and excited states counteracts this variation, leading to only minor net changes of the observed spectra.T he fit of the observed chemical shifts provided a value of 288.0 AE 4.5 cm À1 for the energy separation in favor of the doublet state.…”

“…[13] Notably,s imilar vanadium complexes with ar elated ligand have been described previously. [14] As summarized in Scheme 1, the Ln(Ph-BIAN) 3 compounds were obtained in high yields. Due to their neutralc harge, they are soluble in common organic solvents and can therefore be isolated by extraction with toluene as intensely red solids.T he stoichiometry of the reaction should be met exactly to avoid the formation of toluene-soluble byproducts.T he compounds are very sensitivet oa ir and moisture, particularly in solution, and have to be handled accordingly.All compoundswere char-acterizedb yN MR spectroscopy and elemental analysis.…”

Ferrous complexes supported by sterically encumbered asymmetric bis(arylimino)acenaphthene (BIAN) ligands: synthesis, characterization and screening for catalytic hydrosilylation of carbonyl compounds

“…[11][12][13][14][15] In recent years, Clark and co-authors explored the reactivity and redox capability of BIAN ligands in early transition metal complexes, revealing very rich electronic behavior for such metal/ligand combination. 16,17 In contrast, iron compounds bearing BIAN ligand framework are relatively less investigated. A search in Cambridge Structural Database (CSD) showed that only several structurally characterized BIAN-Fe complexes have been reported, including those with tridentate BIAN ligands with an additional donor arm other than the two N donors.…”