Synthesis and Characterization of a Neutral Titanium Tris(iminosemiquinone) Complex Featuring Redox-Active Ligands

Abstract

The neutral tris(semiquinonate) complex [Ti(dmp-BIAN(isq))(3)] [dmp-BIAN(isq) = N,N'-bis(3,5-dimethylphenylimino)acenaphthenesemiquinonate] was structurally, spectroscopically, and electrochemically characterized. Solid-state magnetism experiments reveal field-quenchable, enhanced temperature-independent paramagnetism (TIP). Density functional theory calculations employing the experimental geometry predicts a strong antiferromagnetic coupling, leading to an S = 0 ground state, but they also hint at spin frustration and concomitant close-lying, excited states, which cause the observed large TIP by admixture into the ground state. The dmp-BIAN(isq) ligand, which facilitates intramolecular electron transfer, was shown to undergo four quasi-reversible redox processes, demonstrating the ability of the ligand to act as an electron reservoir in complexes of early metals.

Structure, magnetic properties and electronic structure of a nickel(II) complex with redox-active 6-(8-quinolylamino)-2,4-bis(tert-butyl)phenol

“…We are also interested in the magnetic properties of complexes containing redox active ligands, in particular, semiquinone or iminosemiquinone-based ligands, where temperature dependent electron transfer reactions are often observed with cobalt (in so-called valence tautomerism) [6]. There are fewer examples of iminosemiquinone complexes relative to the parent semiquinone but iminosemiquinone systems are easy to prepare and can present a wide variety of structural types by variation of the amine in the synthesis [7][8][9][10]. In 2004 Wieghardt and co-workers described the preparation of 1 (Fig.…”

Delocalization and Valence Tautomerism in Vanadium Tris(iminosemiquinone) Complexes

“…[4] Recently,wereported the isolation of the neutral titanium tris(semiquinonate) complex, which was supported by the a-diimine ligand N,N'-bis (3,5-dimethylphenylimino)acenaphthenesemiquinonate (dmp-BIAN isq ;LC), and was found to not only undergo intramolecular electron transfer (IET), but also displayed unprecedented field-quenched, enhanced temperature-independent paramagnetism (TIP). [5] This class of ligands are able to coordinate to metal centers in multiple oxidation states, [6] and are known for electronic flexibility, including IET,w ith main-group, [7] late transition, [8] and f-block metals. [9] Studies of the interactions between these ligands and early transition metals,h owever, are quite limited.…”

Delocalization and Valence Tautomerism in Vanadium Tris(iminosemiquinone) Complexes

“…Thesix reversible one-electron waves occur at À3.62 V, À2.65 V, À1.97 V, À1.07 V, À0.68 V, and + 0.46 V (7) 77.98(9) N(1) eq -V-N(1) eq 91.64 (7) 90.39 (8) 90.31 (7) 90.41 (8) These data unambiguously illustrate the changes in oxidation state associated with the monocation 2.T he presence of 1 HNMR resonances and the absence of an EPR signal strongly suggest an even spin system. [5] Thes imilarities between these vanadium complexes and their titanium analogues lend further support to the conclusion that their observed electrochemical behaviour arises from molecular orbitals with significant ligand character. The transition to S = 1a th igh temperatures is corroborated by changes in intraligand and ligand-metal bond lengths.T hese changes indicate that at low temperatures,t he ligand configuration is identical to that of 1,and the only difference is the vanadium oxidation state.Whenthe temperature is increased, an electron is transferred from al igand to the metal center.…”

“…[2] Homoleptic complexes provide ap ath for extracting this information, as their high inherent symmetry facilitates electronic and structure treatments to provide parameters that can simplify analyses of more complex systems. [5] This class of ligands are able to coordinate to metal centers in multiple oxidation states, [6] and are known for electronic flexibility, including IET,w ith main-group, [7] late transition, [8] and f-block metals. [5] This class of ligands are able to coordinate to metal centers in multiple oxidation states, [6] and are known for electronic flexibility, including IET,w ith main-group, [7] late transition, [8] and f-block metals.…”