TY - JOUR
T1 - Ligand macrocycle structural effects on copper-dioxygen reactivity
AU - Lam, Bernice M.T.
AU - Halfen, Jason A.
AU - Young, Victor G.
AU - Hagadorn, John R.
AU - Holland, Patrick L.
AU - Lledós, Agustí
AU - Cucurull-Sánchez, Lourdes
AU - Novoa, Juan J.
AU - Alvarez, Santiago
AU - Tolman, William B.
PY - 2000/9/4
Y1 - 2000/9/4
N2 - With the goal of understanding how the nature of the tridentate macrocyclic supporting ligand influences the relative stability of isomeric μ-η2:η2-peroxo- and bis(μ-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 °C yielded bis(μ-oxo) species [(R3TACD)2Cu2(μO)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(μ-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 μ-η2:η2-peroxo product, with no trace of the bis(μ-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 α 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(μ-hydroxo)- and μ-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(μ-oxo) forms, and the nature of this influence was shown by both theory and experiment to depend on the ligand macrocycle ring size.
AB - With the goal of understanding how the nature of the tridentate macrocyclic supporting ligand influences the relative stability of isomeric μ-η2:η2-peroxo- and bis(μ-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 °C yielded bis(μ-oxo) species [(R3TACD)2Cu2(μO)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(μ-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 μ-η2:η2-peroxo product, with no trace of the bis(μ-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 α 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(μ-hydroxo)- and μ-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(μ-oxo) forms, and the nature of this influence was shown by both theory and experiment to depend on the ligand macrocycle ring size.
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U2 - 10.1021/ic000248p
DO - 10.1021/ic000248p
M3 - Article
C2 - 11198861
AN - SCOPUS:18244411287
SN - 0020-1669
VL - 39
SP - 4059
EP - 4072
JO - Inorganic Chemistry
JF - Inorganic Chemistry
IS - 18
ER -