Terthienyl and poly-terthienyl ligands as redox-switchable hemilabile ligands for oxidation-state-dependent molecular uptake and release

Mononuclear, dinuclear, and polymeric Ru(II) complexes formed from, terthie nylalkylphosphino redox-switchable hemilabile ligands demonstrate that this class of ligand provides electrochemical control over the electronic prope rties, coordination environments, and reactivities of bound transition meta ls. Specifically, [CpRuCO(K-2-3(')-(2-diphenylphosphinoethyl)-5,5 " -dimeth yl-2,2 ' :5 ' ,2 " -terthiophene)][B(C6H3-3,5-(CF3)(2))(4)] (4a) exhibits a 3 orders of magnitude increase in binding affinity for acetonitrile upon t erthienyl-based oxidation. FT-IR spectroelectrochemical experiments on 4a i ndicate that terthienyl-based oxidation removes electron density from the m etal center, equivalent to approximately 11-17% of the electronic change th at occurs upon direct oxidation of Ru(II) to Ru(III) in analogous complexes . The spectroelectrochemical responses of 4a were compared to those of dime ric and polymeric analogues, of 4a. The spectroelectrochemistry of the dime r is; consistent with two sequential, one-electron ligand-based oxidations, compared to only one in 4a. In contrast, the polymer exhibits spectroelect rochemical behavior similar to that of 4a. The polymer spectroelectrochemis try shows changes in the metal center electronic properties between two dif ferent states, reflective of two discrete oxidation states of the polymeric ligand backbone: We propose that the polymer backbone does not allow one t o vary the electronic properties of the metal center through a continuous r ange of oxidation states due to charge localization within the metalated fi lms. In an effort to explore the molecular uptake and release properties of 4a and its polymer analogue;asa function of ligand oxidation state, the ox idation-state-dependent coordination chemistries of 4a and 4a(+) with a var iety of substrates were examined.