Robert R. Gagne

Bio: Robert R. Gagne is an academic researcher from Stanford University. The author has contributed to research in topics: Copper & Reactivity (chemistry). The author has an hindex of 25, co-authored 37 publications receiving 2824 citations.

Binuclear complexes of macrocyclic ligands: electrochemical and spectral properties of homobinuclear Cu/sup II/Cu/sup II/, Cu/sup II/Cu/sup I/, and Cu/sup I/Cu/sup I/ species including an estimated intramolecular electron transfer rate

Abstract: Electrochemical techniques were employed to study electron transfer properties of a binuclear copper--macrocyclic ligand complex and to prepare several reduced derivatives. The complex, Cu/sup II/Cu/sup II/L(ClO/sub 4/)/sub 2/.2H/sub 2/O, was prepared by condensing 1,3-diaminopropane with 5-methyl-2-hydroxyisophthalaldehyde and Cu(ClO/sub 4/)/sub 2/.6H/sub 2/O. The Cu/sup II/Cu/sup II/ complex was reduced in successive, quasi-reversible, one-electron steps at - 0.52 and - 0.91 V vs. NHE. Constant-potential electrolysis was employed to prepare the reduced species, Cu/sup II/Cu/sup I/L(ClO/sub 4/) and Cu/sup I/Cu/sup I/L, both of which were isolated and fully characterized. The mixed-valence species, Cu/sup II/Cu/sup I/L/sup +/, is stable in oxygen-free solutions (conproportionation constant: 3.97 x 10/sup 6/) and reacts with carbon monoxide to form an adduct, Cu/sup II/Cu/sup I/L(CO)ClO/sub 4/. The diamagnetic Cu/sup I/Cu/sup I/L species was obtained as essentially insoluble black needles which, however, formed a soluble dicarbonyl adduct, Cu/sup I/Cu/sup I/L(CO)/sub 2/, on exposure to CO. The latter complex was not isolated. At the ambient temperature Cu/sup II/Cu/sup I/L/sup +/ exhibits an isotropic seven-line solution EPR spectrum while an anisotropic pattern was observed in frozen solutions (77/sup 0/K), with four lines for g parallel to and unresolved g perpendicular to. Variable-temperature experiments indicated coalescence at about 200/sup 0/K suggesting anmore » intramolecular electron transfer rate of about 1.7 x 10/sup 10/ s/sup -1/ at 298/sup 0/K. Electronic absorption spectral measurements revealed at least two absorptions for Cu/sup II/Cu/sup I/L(ClO/sub 4/)/sub 2/ at 1700 and 1200 nm (CH/sub 2/Cl/sub 2/), which are not present in Cu/sup II/Cu/sup II/L(ClO/sub 4/)/sub 2/.2H/sub 2/O, Cu/sup I/Cu/sup I/L, or the carbonyl derivatives. The new spectral bands may be attributable to intramolecular electron transfer processes. 11 figures, 5 tables.« less

Structure of an Iron(II) Dioxygen Complex; A Model for Oxygen Carrying Hemeproteins

Abstract: The preliminary structural characterization of a reversible ferrous dioxygen complex is reported. Mono(N-methyl imidazole) (dioxygen) meso-tetra (α,α,α,α-o-pivalamidephenyl) porphinatorino(II), [Fe(O2)-(N-Me imid) (α,α,α,α-TpivPP)], 1, isolated from toluene solution, crystallizes in the monoclinic system with four molecules in a unit cell of dimensions a = 18.690 (3), b = 19.514 (3), c = 18.638 (3) A, and β = 91.00 (1)°. R = 0.15 for 841 reflections having F2 > 3σ (F2). The complex 1 has four pivalamido groups on one side of the porphyrin forming a hydrophobic pocket of 5.4-A depth which encloses coordinated dioxygen. The dioxygen is coordinated “end-on,” with a bent Fe-O-O bond. The Fe-O-O plane bisects an N-Fe-N right angle of the equatorial iron porphyrin plane and is four way statistically disordered. In addition there is a crystallographic 2-fold axis through iron, coordinated oxygen, and nitrogen of the axially bound N-methyl imidazole. Thus there are two types of coordinated dioxygen with the Fe-O-O plane either parallel or perpendicular to the trans axial imidazole plane. Corresponding values for the Fe-O-O bond angles are 135-(4)° and 137(4)° and for the O-O bond lengths are 1.23 (0.08) and 1.26 (0.08) A, with a dihedral angle of 90° between alternative orientations of the Fe-O-O plane. The Fe-O distance is 1.75 (0.02) A and Fe-N (imidazole) is 2.07 (0.02) A, suggesting multiple bond character in the Fe-O moiety. The similarity of the Mossbauer spectrum of the model complex, 1, with oxyhemoglobin indicates that 1 may be a good model for oxygen binding in the oxygen transport hemeproteins.