Titanium(IV) Complexes of Disulfide-Linked Schiff Bases

With the goal of preparing Ti(IV) complexes bearing a sulfur-based redox function of possible use in electrocatalytic oxidations of alcohols at electrode surfaces, a series of seven 2,2'-dithiodianiline Schiff-base derivatives, including two new variations, were tested in reactions with Ti(OR)(4) (R = Pr-i, Bu-t). Instead of the expected dimetallic products of general formula [LTi(OR)(2)](2), mononuclear species LTi(OR)(2) were obtained, confirmed by crystallographic determinations to have an unprecedented, symmetrical, and macrocyclic arrangement with four-point binding to the metal center and with the disulfide moieties remaining uncoordinated. Cyclic voltammetry performed in CH2Cl2 displayed oxidations at potentials useful for fuel cells (+1.1-1.5 V vs Ag/AgCl), but despite the uncoordinated disulfide moieties, the complexes were reticent to engage in reduction processes.