title: Combination of redox-active ligand and lewis acid for dioxygen reduction with π-bound molybdenum-quinonoid complexes.
abstract: A series of π-bound Mo-quinonoid complexes supported by pendant phosphines have been synthesized. Structural characterization revealed strong metal-arene interactions between Mo and the π system of the quinonoid fragment. The Mo-catechol complex (2a) was found to react within minutes with 0.5 equiv of O(2) to yield a Mo-quinone complex (3), H(2)O, and CO. Si- and B-protected Mo-catecholate complexes also react with O(2) to yield 3 along with (R(2)SiO)n and (ArBO)(3) byproducts, respectively. Formally, the Mo-catecholate fragment provides two electrons, while the elements bound to the catecholate moiety act as acceptors for the O(2) oxygens. Unreactive by itself, the Mo-dimethyl catecholate analogue reduces O(2) in the presence of added Lewis acid, B(C(6)F(5))(3), to generate a Mo(I) species and a bis(borane)-supported peroxide dianion, [[(F(5)C(6))(3)B](2)O(2)(2-)], demonstrating single-electron-transfer chemistry from Mo to the O(2) moiety. The intramolecular combination of a molybdenum center, redox-active ligand, and Lewis acid reduces O(2) with pendant acids weaker than B(C(6)F(5))(3). Overall, the π-bound catecholate moiety acts as a two-electron donor. A mechanism is proposed in which O(2) is reduced through an initial one-electron transfer, coupled with transfer of the Lewis acidic moiety bound to the quinonoid oxygen atoms to the reduced O(2) species.
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology , 1200 East California Boulevard, MC 127-72, Pasadena, California 91125, United States.
authors.forename: Justin T
authors.initials: JT
authors.lastname: Henthorn
authors.forename: Sibo
authors.initials: S
authors.lastname: Lin
authors.forename: Theodor
authors.initials: T
authors.lastname: Agapie
mesh_terms: D016227:Benzoquinones / Q000737:chemistry*; D002396:Catechols / Q000737:chemistry; D056831:Coordination Complexes / Q000737:chemistry*; D058116:Lewis Acids / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D008982:Molybdenum / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*
chemical_list: D016227:Benzoquinones; D002396:Catechols; D056831:Coordination Complexes; D058116:Lewis Acids; D008024:Ligands; C004532:quinone; D008982:Molybdenum; C034221:catechol; D010100:Oxygen