184219-38-3Relevant academic research and scientific papers
Ligand macrocycle structural effects on copper-dioxygen reactivity
Lam, Bernice M. T.,Halfen, Jason A.,Young Jr., Victor G.,Hagadorn, John R.,Holland, Patrick L.,Lledos, Agusti,Cucurull-Sanchez, Lourdes,Novoa, Juan J.,Alvarez, Santiago,Tolman, William B.
, p. 4059 - 4072 (2008/10/08)
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.
Structural, spectroscopic, and theoretical characterization of bis(μ-oxo)dicopper complexes, novel intermediates in copper-mediated dioxygen activation
Mahapatra, Samiran,Halfen, Jason A.,Wilkinson, Elizabeth C.,Pan, Gaofeng,Wang, Xuedong,Young Jr., Victor G.,Cramer, Christopher J.,Que Jr., Lawrence,Tolman, William B.
, p. 11555 - 11574 (2007/10/03)
A description of the structure and bonding of novel bis(μ-oxo)dicopper complexes and their bis(μ-hydroxo)dicopper decomposition products was derived from combined X-ray crystallographic, spectroscopic, and ab initio theoretical studies. The compounds [(LCu)2(μ-O)2]X2 were generated from the reaction of solutions of [LCu(CH3CN)]X with O2 at -80 °C (L = 1,4,7-tribenzyl-1,4,7-triazacyclononane, L(Bn3); 1,4,7-triisopropyl-1,4,7-triazacyclononane, L(iPr3); or 1-benzyl-4,7-diisopropyl-1,4,7-triazacyclononane, L(iPr2Bn); X = variety of anions). The geometry of the [Cu2(μ-O)2]2+ core was defined by X-ray crystallography for [(d21-L(Bn3)Cu)2(μ-O)2](SbF6)2 and by EXAFS spectroscopy for the complexes capped by L(Bn3) and L(iPr3); notable dimensions include short Cu-O (~1.80 A?) and Cu···Cu (~2.80 A?) distances like those reported for analogous M2(μ-O)2 (M = Fe or Mn) rhombs. The core geometry is contracted compared to those of the bis(μ-hydroxo)dicopper(II) compounds that result from decomposition of the bis(μ-oxo) complexes upon warming. X-ray structures of the decomposition products [(L(Bn3)Cu)(L(Bn2H)Cu)(μ-OH)2](O3SCF3)2·2CH3CO, [(L(iPr2H)Cu)2(μ-OH)2](BPh4)2·2THF, and [(L(iPr2Bn)Cu)2(μ-OH)2](O3SCF3)2 showed that they arise from N-dealkylation of the original capping macrocycles. Manometric, electrospray mass spectrometric, and UV-vis, EPR, NMR, and resonance Raman spectroscopic data for the bis(μ-oxo)dicopper complexes in solution revealed important topological and electronic structural features of the intact [Cu2(μ-O)2]2+ core. The bis(μ-oxo)dicopper unit is diamagnetic, undergoes a rapid fluxional process involving interchange of equatorial and axial N-donor ligand environments, and exhibits a diagnostic ~600 cm-1 18O-sensitive feature in Raman spectra. Ab initio calculations on a model system, {[(NH3)3Cu]2(μ-O)2}2+, predicted a closed-shell singlet ground-state structure that agrees well with the bis(μ-oxo)dicopper geometry determined by experiment and helps to rationalize many of its physicochemical properties. On the basis of an analysis of the theoretical and experimental results (including a bond valence sum analysis), a formal oxidation level assignment for the core is suggested to be [Cu(III)(μ-O2-)2]2+, although a more complete molecular orbital description indicates that the oxygen and copper fragment orbitals are significantly mixed (i.e., there is a high degree of covalency).
