Copper−Dioxygen Adducts and the Side-on Peroxo Dicopper(II)/Bis(μ-oxo) Dicopper(III) Equilibrium: Significant Ligand Electronic Effects

The variation of ligand para substituents on pyridyl donor groups of tridentate amine copper(I) complexes was
carried out in order to probe electronic effects on the equilibrium between μ-η2:η2-(side-on)-peroxo [CuII2(O22-)]2+
and bis(μ-oxo) [CuIII2(O2-)2] species formed upon reaction with O2. [CuI(R-PYAN)(MeCN)n]B(C6F5)4 (R-PYAN =
N-[2-(4-R-pyridin-2-yl)-ethyl]-N,N‘,N‘-trimethyl-propane-1,3-diamine, R = NMe2, OMe, H, and Cl) (1R) vary over a
narrow range in their CuII/CuI redox potentials (E1/2 vs Fe(cp)2+/0 = −0.40 V for 1NMe2, −0.38 V for 1OMe, −0.33 V
for 1H, and −0.32 V for 1Cl) and in C−O stretching frequencies of their carbonyl adducts, 1R−CO:  ν(C−O) = 2080,
2086, 2088, and 2090 cm-1 for R = NMe2, OMe, H, and Cl, respectively. However, within this range of electronic
properties for 1R, dioxygen reactivity is significantly affected. The reaction of 1Cl or 1H with O2 at −78 °C in CH2Cl2
gives UV−vis and resonance Raman spectra indicative of a μ-η2:η2-(side-on)-peroxo dicopper(II) adduct (2R).
Compound 1OMe reacts with O2, yielding equilibrium mixtures of side-on peroxo (2OMe) and bis(μ-oxo) (3OMe) species.
Oxygenation of 1NMe2 leads to the sole generation of the bis(μ-oxo) dicopper(III) complex (3NMe2). A solvent effect
was also observed; in acetone or THF, increased ratios of bis(μ-oxo) relative to side-on peroxo complex are
observed. Thus, the equilibrium between a dicopper side-on peroxo and bis(μ-oxo) species can be tuned by ligand
designspecifically, more electron donating ligands favor the formation of the latter isomer, and the peroxo/bis(μ-oxo) equilibrium can be shifted from one extreme to the other within the same ligand system. Observations
concerning the reactivity of the dioxygen adducts 2H and 3NMe2 toward external substrates are also presented.

本研究旨在探究配体在吡啶供体基团上的取代基变化对三齿胺铜(I)配合物的影响，以揭示其对μ-η2:η2-(侧向)-过氧[CuII2(O22-)]2+与双(μ-氧化物)[CuIII2(O2-)2]物种在氧气反应中的平衡电子效应。配合物[CuI(R-PYAN)(MeCN)n]B(C6F5)4（R-PYAN = N-[2-(4-R-吡啶-2-基)-乙基]-N,N'，N''-三甲基丙烷-1,3-二胺，R = NMe2, OMe, H, 和 Cl）(1R)的CuII/CuI氧化还原电位（以Fe(cp)2+/0的E1/2 = −0.40 V为基准，1NMe2为−0.38 V，1OMe为−0.33 V，1H为−0.32 V，1Cl为−0.32 V）以及其羰基加成物的C−O伸缩振动频率（R = NMe2时ν(C−O) = 2080 cm-1，R = OMe时ν(C−O) = 2086 cm-1，R = H时ν(C−O) = 2088 cm-1，R = Cl时ν(C−O) = 2090 cm-1）在狭窄范围内变化。然而，在此电子性质范围内，1R与氧气反应的活性显著受影响。在-78 °C下，1Cl或1H与氧气在CH2Cl2中的反应产生了表明μ-η2:η2-(侧向)-过氧二铜(II)加成物(2R)的紫外-可见光谱和共振拉曼光谱。化合物1OMe与氧气反应，生成了侧向过氧(2OMe)和双(μ-氧化物)(3OMe)物种的平衡混合物。1NMe2的氧化产生了单一的双(μ-氧化物)二铜(III)配合物(3NMe2)。还观察到溶剂效应；在丙酮或THF中，相对于侧向过氧配合物，双(μ-氧化物)配合物的比例增加。因此，通过配体设计可以调节二铜侧向过氧与双(μ-氧化物)物种之间的平衡，特别是电子供体配体有利于后者的形成，并且过氧/双(μ-氧化物)平衡可以在同一配体系统中从一端移动到另一端。还呈现了二氧化物加成物2H和3NMe2对外部底物的反应活性观察结果。