Molecular Capacitors: Accessible 6- and 8-Electron Redox Chemistry from Dimeric "Ti(I)" and "Ti(0)" Synthons Supported by Imidazolin-2-Iminato Ligands.

Reduction of the diamagnetic Ti(III)/Ti(III) dimer [ClTi(μ-NIm)] () (NIm = [1,3-bis(Dipp)imidazolin-2-iminato], Dipp = CH-2,6-Pr) with 4 and 6 equiv of KC generates the intramolecularly arene-masked, dinuclear titanium compounds [(μ-N-η-Im)Ti] () and {[(EtO)K](μ-N-μ:η-Im)Ti} (), respectively, in modest yields. The compounds have been structurally characterized by X-ray crystallographic analysis, and inspection of the bond metrics within the η-coordinated aryl substituent of the bridging imidazolin-2-iminato ligand shows perturbation of the aromatic system most consistent with two-electron reduction of the ring. As such, and can be assigned respectively as possessing metal centers in formal Ti(III)/Ti(III) and Ti(II)/Ti(II) oxidation states. Exploration of their redox chemistry reveal the ability to reduce several substrate equivalents. For instance, treatment of with excess CH (COT) forms the novel COT-bridged complex [(ImN)(η-COT)Ti](μ-η:η-COT)[Ti(η-COT)(NIm)] () that dissociates in THF solutions to give mononuclear (ImN)Ti(η-COT)(THF) (). Addition of COT to yields heterometallic [(ImN)(η-COT)Ti(μ-η:η-COT)K(THF)(μ-η:η-COT)Ti(NIm)(μ-η:η-COT)K(THF)] (). Compounds and are the products of the 4-electron oxidation of , while stands as the 8-electron oxidation product of . Reduction of organozides was also explored. Low temperature reaction of with 4 equiv of AdN gives the terminal and bridged imido complex [(ImN)Ti(═NAd)](μ-NAd)[Ti(NIm)(NAd)] () that undergoes intermolecular C-H activation of toluene at room temperature to afford the amido compound [(ImN)Ti(NHAd)](μ-NAd)[Ti(CHMe)(NIm)] (). These complexes are the 6-electron oxidation products of the reaction of with AdN. Furthermore, treatment of with 4 equiv of AdN produces the thermally stable Ti(III)/Ti(III) terminal and bridged imido [K(18-crown-6)(THF)]{[(ImN)Ti(NAd)](μ-NAd)K[Ti(NIm)]} (). Altogether, these reactions firmly establish and as unprecedented Ti(I)/Ti(I) and Ti(0)/Ti(0) synthons with the clear capacity to effect multielectron reductions ranging from 4 to 8 electrons.