title: Ligand macrocycle structural effects on copper-dioxygen reactivity.
abstract: With the goal of understanding how the nature of the tridentate macrocyclic supporting ligand influences the relative stability of isomeric mu-eta 2:eta 2-peroxo- and bis(mu-oxo)dicopper complexes, a comparative study was undertaken of the O2 reactivity of Cu(I) compounds supported by the 10- and 12-membered macrocycles, 1,4,7-R3-1,4,7-triazacyclodecane (R3TACD; R = Me, Bn, iPr) and 1,5,9-triisopropyl-1,5,9-triazacyclododecane (iPr3TACDD). While the 3-coordinate complex [(iPr3TACDD)Cu]SbF6 was unreactive with O2, oxygenation of [(R3TACD)Cu(CH3CN)]X (R = Me or Bn; X = ClO4- or SbF6-) at -80 degrees C yielded bis(mu-oxo) species [(R3TACD)2Cu2(mu O)2]X2 as revealed by UV-vis and resonance Raman spectroscopy. Interestingly, unlike the previously reported system supported by 1,4,7-triisopropyl-1,4,7-triazacyclononane (iPr3TACN), which yielded interconverting mixtures of peroxo and bis(mu-oxo) compounds (Cahoy, J.; Holland, P. L.; Tolman, W. B. Inorg. Chem. 1999, 38, 2161), low-temperature oxygenation of [(iPr3TACD)Cu(CH3CN)]SbF6 in a variety of solvents cleanly yielded a mu-eta 2:eta 2-peroxo product, with no trace of the bis(mu-oxo) isomer. The peroxo complex was characterized by UV-vis and resonance Raman spectroscopy, as well as an X-ray crystal structure (albeit of marginal quality due to disorder problems). Intramolecular attack at the alpha C-H bonds of the substituents was indicated as the primary decomposition pathway of the oxygenated compounds through examination of the decay kinetics and the reaction products, which included bis(mu-hydroxo)- and mu-carbonato-dicopper complexes that were characterized by X-ray diffraction. A rationale for the varying results of the oxygenation reactions was provided by analysis of (a) the X-ray crystal structures and electrochemical behavior of the Cu(I) precursors and (b) the results of theoretical calculations of the complete oxygenated complexes, including all ligand atoms, using combined quantum chemical/molecular mechanics (integrated molecular orbital molecular mechanics, IMOMM) methods. The size of the ligand substituents was shown to be a key factor in controlling the relative stabilities of the peroxo and bis(mu-oxo) forms, and the nature of this influence was shown by both theory and experiment to depend on the ligand macrocycle ring size.
authors.affiliation: Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, USA.
authors.forename: B M
authors.initials: BM
authors.lastname: Lam
authors.forename: J A
authors.initials: JA
authors.lastname: Halfen
authors.forename: V G
authors.initials: VG
authors.lastname: Young
authors.forename: J R
authors.initials: JR
authors.lastname: Hagadorn
authors.forename: P L
authors.initials: PL
authors.lastname: Holland
authors.forename: A
authors.initials: A
authors.lastname: Lledós
authors.forename: L
authors.initials: L
authors.lastname: Cucurull-Sánchez
authors.forename: J J
authors.initials: JJ
authors.lastname: Novoa
authors.forename: S
authors.initials: S
authors.lastname: Alvarez
authors.forename: W B
authors.initials: WB
authors.lastname: Tolman
mesh_terms: D003300:Copper / Q000737:chemistry*; D004563:Electrochemistry; D008024:Ligands; D008958:Models, Molecular; D015394:Molecular Structure; D010100:Oxygen / Q000737:chemistry*
chemical_list: D008024:Ligands; D003300:Copper; D010100:Oxygen