title: Three-way cooperativity in d8 metal complexes with ligands displaying chemical and redox non-innocence.
abstract: Reversible proton- and electron-transfer steps are crucial for various chemical transformations. The electron-reservoir behavior of redox non-innocent ligands and the proton-reservoir behavior of chemically non-innocent ligands can be cooperatively utilized for substrate bond activation. Although site-decoupled proton- and electron-transfer steps are often found in enzymatic systems, generating model metal complexes with these properties remains challenging. To tackle this issue, we present herein complexes [(cod-H)M(μ-L(2-)) M(cod-H)] (M = Pt(II), [1] or Pd(II), [2], cod = 1,5-cyclooctadiene, H2L = 2,5-di-[2,6-(diisopropyl)anilino]-1,4-benzoquinone), in which cod acts as a proton reservoir, and L(2-) as an electron reservoir. Protonation of [2] leads to an unusual tetranuclear complex. However, [1] can be stepwise reversibly protonated with up to two protons on the cod-H ligands, and the protonated forms can be stepwise reversibly reduced with up to two electrons on the L(2-) ligand. The doubly protonated form of [1] is also shown to react with OMe(-) leading to an activation of the cod ligands. The site-decoupled proton and electron reservoir sources work in tandem in a three-way cooperative process that results in the transfer of two electrons and two protons to a substrate leading to its double reduction and protonation. These results will possibly provide new insights into developing catalysts for multiple proton- and electron-transfer reactions by using metal complexes of non-innocent ligands.
authors.affiliation: Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart (Germany).
authors.forename: Naina
authors.initials: N
authors.lastname: Deibel
authors.forename: Stephan
authors.initials: S
authors.lastname: Hohloch
authors.forename: David
authors.initials: D
authors.lastname: Schweinfurth
authors.forename: Fritz
authors.initials: F
authors.lastname: Weisser
authors.forename: Anita
authors.initials: A
authors.lastname: Grupp
authors.forename: Biprajit
authors.initials: B
authors.lastname: Sarkar
mesh_terms: D000466:Alkadienes / Q000737:chemistry*; D016227:Benzoquinones / Q000737:chemistry*; D056831:Coordination Complexes / Q000737:chemistry*; D004579:Electron Transport; D004583:Electrons; D008024:Ligands; D008958:Models, Molecular; D010084:Oxidation-Reduction; D011522:Protons
chemical_list: D000466:Alkadienes; D016227:Benzoquinones; D056831:Coordination Complexes; D008024:Ligands; D011522:Protons; C439868:1,5-cyclooctadiene; C004532:quinone
keywords: bond activation; electron transfer; ligand effects; quinones; spectroelectrochemistry