Solvent effects on the conversion of dicopper(II) micro-eta(2):eta(2)-peroxo to bis-micro-oxo dicopper(III) complexes: direct probing of the solvent interaction.
A new tridentate ligand, PYAN, is employed to investigate solvent influences for dioxygen reactivity with [Cu(PYAN)(MeCN)]B(C(6)F(5))(4) (1). Stopped-flow kinetic studies confirm that the adducts [[u(II)(PYAN)]2)(O(2))][B(C(6)F(5))(4)](2) (2(Peroxo)) and [[u(III)(PYAN)]2)(O)(2)][B(C(6)F(5))(4)](2) (2(Oxo)) are in rapid equilibrium. Thermodynamic parameters for the equilibrium between 2(Peroxo) and 2(Oxo) re as follows: THF, deltaH degrees approximately -15.7 kJ/mol, deltaS degrees approximately -83 J/K.mol; acetone, deltaH degrees approximately -15.8 kJ/mol, deltaS degrees approximately -76 J/K.mol. UV-visible absorption and resonance Raman spectroscopic signatures demonstrate that the equilibrium is highly solvent dependent; the mixture is mostly 2(Peroxo) in CH(2)Cl(2), but there are significantly increasing quantities of 2(Oxo) along the series methylene chloride --> diethyl ether --> acetone --> tetrahydrofuran (THF). Copper(II)-N(eq) stretches (239, 243, 244, and 246 cm(-)(1) in CH(2)Cl(2), Et(2)O, acetone, and THF, respectively) are identified for 2(Peroxo), but they are not seen in 2(Oxo), revealing for the first time direct evidence for solvent coordination in the more open 2(Peroxo) structure.
Liang
Hong-Chang
HC
Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, USA.
Henson
Mark J
MJ
Hatcher
Lanying Q
LQ
Vance
Michael A
MA
Zhang
Christiana Xin
CX
Lahti
David
D
Kaderli
Susan
S
Sommer
Roger D
RD
Rheingold
Arnold L
AL
Zuberbühler
Andreas D
AD
Solomon
Edward I
EI
Karlin
Kenneth D
KD
D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D012997:Solvents; D013059:Spectrum Analysis, Raman / Q000379:methods
D009942:Organometallic Compounds; D012997:Solvents; D003300:Copper; D010100:Oxygen