title: Tuning copper-dioxygen reactivity and exogenous substrate oxidations via alterations in ligand electronics.
abstract: Copper(I)-dioxygen adducts are important in biological and industrial processes. For the first time we explore the relationship between ligand electronics, CuI-O2 adduct formation and exogenous substrate reactivity. The copper(I) complexes [CuI(R-MePY2)]+ (1R, where R = Cl, H, MeO, Me2N) were prepared; where R-MePY2 are 4-pyridyl substituted bis[2-(2-pyridyl)ethyl]methylamine chelates. Both the redox potential of 1R (ranging from E1/2 = -270 mV for 1Cl to -440 mV for 1MeN vs FeCp2/FeCp2+) and nuCO of the CO adducts of 1R (ranging from 2093 cm-1 for 1Cl-CO to 2075 cm-1 for 1Me2N-CO) display modest but expected systematic shifts. Dioxygen readily reacts with 1H, 1MeO, and 1Me2N, forming the side-on peroxo-CuII2 complexes [{CuII(R-MePY2)}2(O2)]2+ (2R, also containing some bis-mu-oxo-CuIII2 isomer), but there is no reaction with 1Cl. Stopped-flow studies in dichloromethane show that the formation of 2Me2N from dioxygen and 1Me2N proceeds with a k = 8.2(6) x 104 M-2 s-1 (183 K, DeltaH = -20.3(6) kJ mol-1, DeltaS = -219(3) J mol-1 K-1). Solutions of 2R readily oxidize exogenous substrates (9,10-dihydroanthracene --> anthracene, tetrahydrofuran (THF) --> 2-hydroxytetrahydrofuran (THF-OH), N,N-dimethylaniline --> N-methylaniline and formaldehyde, benzyl alcohol --> benzaldehyde, benzhydrol --> benzophenone, and methanol --> formaldehyde), forming the bis-mu-hydroxo-CuII2 complexes [{CuII(R-MePY2)(OH)}2]2+ (3R). Product yields increase as the R-group is made more electron-donating, and in some cases are quantitative with 2Me2N. Pseudo-first-order rate constants for THF and methanol oxidation reactions demonstrate a remarkable R-group dependence, again favoring the strongest ligand donor (i.e., R = Me2N). For THF oxidation to THF-OH a nearly 1500-fold increase in reaction rate is observed (kobs = 2(1) x 10-5 s-1 for 2H to 3(1) x 10-2 s-1 for 2Me2N), while methanol oxidation to formaldehyde exhibits an approximately 2000-fold increase (kobs = 5(1) x 10-5 s-1 for 2H to 1(1) x 10-1 s-1 for 2Me2N).
authors.affiliation: Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, USA.
authors.forename: Christiana Xin
authors.initials: CX
authors.lastname: Zhang
authors.forename: Hong-Chang
authors.initials: HC
authors.lastname: Liang
authors.forename: Eun-Il
authors.initials: EI
authors.lastname: Kim
authors.forename: Jason
authors.initials: J
authors.lastname: Shearer
authors.forename: Matthew E
authors.initials: ME
authors.lastname: Helton
authors.forename: Eunsuk
authors.initials: E
authors.lastname: Kim
authors.forename: Susan
authors.initials: S
authors.lastname: Kaderli
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Incarvito
authors.forename: Andreas D
authors.initials: AD
authors.lastname: Zuberbühler
authors.forename: Arnold L
authors.initials: AL
authors.lastname: Rheingold
authors.forename: Kenneth D
authors.initials: KD
authors.lastname: Karlin
mesh_terms: D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D007700:Kinetics; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*
chemical_list: D009942:Organometallic Compounds; D003300:Copper; D010100:Oxygen