title: Geometric and electronic structure of [{Cu(MeAN)}2(μ-η2:η2(O2(2-)))]2+ with an unusually long O-O bond: O-O bond weakening vs activation for reductive cleavage.
abstract: Certain side-on peroxo-dicopper(II) species with particularly low ν(O-O) (710-730 cm(-1)) have been found in equilibrium with their bis-μ-oxo-dicopper(III) isomer. An issue is whether such side-on peroxo bridges are further activated for O-O cleavage. In a previous study (Liang, H.-C., et al. J. Am. Chem. Soc.2002, 124, 4170), we showed that oxygenation of the three-coordinate complex [Cu(I)(MeAN)](+) (MeAN = N-methyl-N,N-bis[3-(dimethylamino)propyl]amine) leads to a low-temperature stable [{Cu(II)(MeAN)}(2)(μ-η(2):η(2)-O(2)(2-))](2+) peroxo species with low ν(O-O) (721 cm(-1)), as characterized by UV-vis absorption and resonance Raman (rR) spectroscopies. Here, this complex has been crystallized as its SbF(6)(-) salt, and an X-ray structure indicates the presence of an unusually long O-O bond (1.540(5) Å) consistent with the low ν(O-O). Extended X-ray absorption fine structure and rR spectroscopic and reactivity studies indicate the exclusive formation of [{Cu(II)(MeAN)}(2)(μ-η(2):η(2)-O(2)(2-))](2+) without any bis-μ-oxo-dicopper(III) isomer present. This is the first structure of a side-on peroxo-dicopper(II) species with a significantly long and weak O-O bond. DFT calculations show that the weak O-O bond results from strong σ donation from the MeAN ligand to Cu that is compensated by a decrease in the extent of peroxo to Cu charge transfer. Importantly, the weak O-O bond does not reflect an increase in backbonding into the σ* orbital of the peroxide. Thus, although the O-O bond is unusually weak, this structure is not further activated for reductive cleavage to form a reactive bis-μ-oxo dicopper(III) species. These results highlight the necessity of understanding electronic structure changes associated with spectral changes for correlations to reactivity.
authors.affiliation: Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, United States.
authors.forename: Ga Young
authors.initials: GY
authors.lastname: Park
authors.forename: Munzarin F
authors.initials: MF
authors.lastname: Qayyum
authors.forename: Julia
authors.initials: J
authors.lastname: Woertink
authors.forename: Keith O
authors.initials: KO
authors.lastname: Hodgson
authors.forename: Britt
authors.initials: B
authors.lastname: Hedman
authors.forename: Amy A
authors.initials: AA
authors.lastname: Narducci Sarjeant
authors.forename: Edward I
authors.initials: EI
authors.lastname: Solomon
authors.forename: Kenneth D
authors.initials: KD
authors.lastname: Karlin
mesh_terms: D056831:Coordination Complexes / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D003959:Diamines / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D010545:Peroxides / Q000737:chemistry*
chemical_list: D056831:Coordination Complexes; D003959:Diamines; D008024:Ligands; D010545:Peroxides; D003300:Copper; C012928:3-dimethylaminopropylamine; D010100:Oxygen