Terthienyl and Poly-terthienyl Ligands as Redox-Switchable Hemilabile Ligands for Oxidation-State-Dependent Molecular Uptake and Release

• Published in: Journal of the American Chemical Society Vol. 123; no. 11; pp. 2503 - 2516
• Main Authors: Weinberger, Dana A, Higgins, Thomas B, Mirkin, Chad A, Stern, Charlotte L, Liable-Sands, Louise M, Rheingold, Arnold L
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 21.03.2001
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja0030008

Mononuclear, dinuclear, and polymeric Ru(II) complexes formed from terthienylalkylphosphino redox-switchable hemilabile ligands demonstrate that this class of ligand provides electrochemical control over the electronic properties, coordination environments, and reactivities of bound transition metals. Specifically, [CpRuCO(κ2-3‘-(2-diphenylphosphinoethyl)-5,5‘ ‘-dimethyl-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 terthienyl-based oxidation. FT-IR spectroelectrochemical experiments on 4a indicate that terthienyl-based oxidation removes electron density from the metal center, equivalent to approximately 11−17% of the electronic change that occurs upon direct oxidation of Ru(II) to Ru(III) in analogous complexes. The spectroelectrochemical responses of 4a were compared to those of dimeric and polymeric analogues of 4a. The spectroelectrochemistry of the dimer is consistent with two sequential, one-electron ligand-based oxidations, compared to only one in 4a. In contrast, the polymer exhibits spectroelectrochemical behavior similar to that of 4a. The polymer spectroelectrochemistry shows changes in the metal center electronic properties between two different states, reflective of two discrete oxidation states of the polymeric ligand backbone. We propose that the polymer backbone does not allow one to vary the electronic properties of the metal center through a continuous range of oxidation states due to charge localization within the metalated films. In an effort to explore the molecular uptake and release properties of 4a and its polymer analogue as a function of ligand oxidation state, the oxidation-state-dependent coordination chemistries of 4a and 4a + with a variety of substrates were examined.