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 [Cl 2 Ti(μ-NIm Dipp )] 2 ( 1 ) (NIm Dipp = [1,3-bis(Dipp)imidazolin-2-iminato] - , Dipp = C 6 H 3 -2,6- i Pr 2 ) with 4 and 6 equiv of KC 8 generates the intramolecularly arene-masked, dinuclear titanium compounds [(μ-N-η 6 -Im Dipp )Ti] 2 ( 2 ) and {[(Et 2 O) 2 K](μ-N-μ -η 6 :η 6 -Im Dipp )Ti} 2 ( 3 ), respectively, in modest yields. The compounds have been structurally characterized by X-ray crystallographic analysis, and inspection of the bond metrics within the η 6 -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, 2 and 3 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 2 with excess C 8 H 8 (COT) forms the novel COT-bridged complex [(Im Dipp N)(η 8 -COT)Ti](μ-η 2 :η 3 -COT)[Ti(η 4 -COT)(NIm Dipp )] ( 4 ) that dissociates in THF solutions to give mononuclear (Im Dipp N)Ti(η 8 -COT)(THF) ( 5 ). Addition of COT to 3 yields heterometallic [(Im Dipp N)(η 4 -COT)Ti(μ-η 4 :η 5 -COT)K(THF)(μ-η 6 :η 4 -COT)Ti(NIm Dipp )(μ-η 4 :η 4 -COT)K(THF) 2 ] n ( 6 ). Compounds 4 and 5 are the products of the 4-electron oxidation of 2 , while 6 stands as the 8-electron oxidation product of 3 . Reduction of organozides was also explored. Low temperature reaction of 2 with 4 equiv of AdN 3 gives the terminal and bridged imido complex [(Im Dipp N)Ti(═NAd)](μ-NAd) 2 [Ti(NIm Dipp )(N 3 Ad)] ( 7 ) that undergoes intermolecular C-H activation of toluene at room temperature to afford the amido compound [(Im Dipp N)Ti(NHAd)](μ-NAd) 2 [Ti(C 6 H 4 Me)(NIm Dipp )] ( 8-tol ). These complexes are the 6-electron oxidation products of the reaction of 2 with AdN 3 . Furthermore, treatment of 3 with 4 equiv of AdN 3 produces the thermally stable Ti(III)/Ti(III) terminal and bridged imido [K(18-crown-6)(THF) 2 ]{[(Im Dipp N)Ti(NAd)](μ-NAd) 2 K[Ti(NIm Dipp )]} ( 10 ). Altogether, these reactions firmly establish 2 and 3 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.