Syntheses, Characterization, and Dioxygen Reactivities of Cu(I) Complexes with cis,cis-1,3,5-Triaminocyclohexane Derivatives: A Cu(III)2O2 Intermediate Exhibiting Higher C−H Activation

Six Cu(I) complexes with cis,cis-1,3,5-triaminocyclohexane derivatives (R3CY, R = Et, iBu, and Bn), [Cu(MeCN)(Et3CY)]SbF6 (1), [Cu(MeCN)(iBu3CY)]SbF6 (2), [Cu(MeCN)(Bn3CY)]SbF6 (3), [Cu(CO)(Et3CY)]SbF6 (4), [Cu(CO)(iBu3CY)]SbF6 (5), and [Cu(CO)(Bn3CY)]SbF6 (6), were prepared to probe the ability of copper complexes to effectively
catalyze oxygenation reactions. The complexes were characterized by elemental analysis, electrochemical and
X-ray structure analyses, electronic absorption spectroscopy, IR spectroscopy, 1H NMR spectroscopy, and ESI
mass spectrometry. The crystal structures of 1−3 and 6 and the CO stretching vibrations (νCO) of 4−6 demonstrate
that the ability of R3CY to donate electron density to the Cu(I) atom is stronger than that of the previously reported
ligands, 1,4,7-triazacyclononane (R3TACN) and 1,4,7-triazacyclodecane (R3TACD). Reactions of complexes 1−3
with dioxygen in THF or CH2Cl2 at −105 to −80 °C yield bis(μ-oxo)dicopper(III) complexes 7−9 as intermediates
as confirmed by electronic absorption spectroscopy and resonance Raman spectroscopy. The Cu−O stretching
vibrations, ν(Cu−O) for 7 (16O2:  553, 581 cm-1and 18O2:  547 cm-1) and 8 (16O2:  571 cm-1 and 18O2:  544 cm-1),
are observed in a lower energy region than previously reported for bis(μ-oxo) complexes. The decomposition rates
of complexes 7−9 in THF at −90 °C are 2.78 × 10-4 for 7, 8.04 × 10-4 for 8, and 3.80 × 10-4 s-1 for 9. The
decomposition rates of 7 and 8 in CH2Cl2 were 5.62 × 10-4 and 1.62 × 10-3 s-1, respectively, and the thermal
stabilities of 7−9 in CH2Cl2 are lower than the values measured for the complexes in THF. The decomposition
reactions obeyed first-order kinetics, and the H/D isotope experiments for 8 and 9 indicate that the N-dealkylation
reaction is the rate-determining step in the decomposition processes. On the other hand, the decomposition reaction
of 7 in THF results in the oxidation of THF (acting as an exogenous substrate) to give 2-hydroxy tetrahydrofuran
and γ-butyrolactone as oxidation products. Detailed investigation of the N-dealkylation reaction for 8 by kinetic
experiments using N−H/D at −90 °C showed a kinetic isotope effect of 1.25, indicating that a weak electrostatic
interaction between the N−H hydrogen and μ-oxo oxygen contributes to the major effect on the rate-determining
step of N-dealkylation. X-ray crystal structures of the bis(μ-hydroxo)dicopper(II) complexes, [Cu2(OH)2(Et3CY)2](CF3SO3)2 (10), [Cu2(OH)2(iBu3CY)2](CF3SO3)2 (11), and [Cu2(OH)2(Bn3CY)2](ClO4)2 (12), which have independently
been prepared as the final products of bis(μ-oxo)dicopper(III) intermediates, suggest that an effective interaction
between N−H and μ-oxo in the Cu(III)2(μ-O)2 core may enhance the oxidation ability of the metal−oxo species.

六种以cis,cis-1,3,5-三氨基环己烷衍生物（R3CY，R分别为Et、iBu和Bn）为配体的Cu(I)配合物[Cu(MeCN)(Et3CY)]SbF6（1）、[Cu(MeCN)(iBu3CY)]SbF6（2）、[Cu(MeCN)(Bn3CY)]SbF6（3）、[Cu(CO)(Et3CY)]SbF6（4）、[Cu(CO)(iBu3CY)]SbF6（5）和[Cu(CO)(Bn3CY)]SbF6（6）已被合成，旨在探究铜配合物催化氧化反应的能力。通过元素分析、电化学和X射线结构分析、电子吸收光谱、红外光谱、1H核磁共振光谱和电喷雾质谱等手段对配合物进行了表征。1−3和6的晶体结构以及4−6的CO伸缩振动（νCO）表明，R3CY向Cu(I)原子捐赠电子密度的能力强于先前报道的配体1,4,7-三氮杂环壬烷（R3TACN）和1,4,7-三氮杂环癸烷（R3TACD）。在-105至-80°C的温度下，复合物1−3与THF或CH2Cl2中的氧气反应，生成双(μ-氧)二铜(III)配合物7−9作为中间体，通过电子吸收光谱和共振拉曼光谱得到证实。7（16O2: 553, 581 cm-1和18O2: 547 cm-1）和8（16O2: 571 cm-1和18O2: 544 cm-1）的Cu-O伸缩振动ν(Cu-O)位于比先前报道的双(μ-氧)配合物更低的能量区域。在-90°C的THF中，复合物7−9的分解速率分别为7（2.78 × 10-4）、8（8.04 × 10-4）和9（3.80 × 10-4 s-1）。在CH2Cl2中，7和8的分解速率分别为5.62 × 10-4和1.62 × 10-3 s-1，而7−9在CH2Cl2中的热稳定性低于THF中的复合物。分解反应遵循一级动力学，8和9的H/D同位素实验表明，N-去烷基化反应是分解过程中的决速步骤。另一方面，7在THF中的分解反应导致THF（作为外源底物）的氧化，生成2-羟基四氢呋喃和γ-丁内酯作为氧化产物。通过在-90°C下使用N-H/D进行的动力学实验详细研究了8的N-去烷基化反应，结果显示动力学同位素效应为1.25，表明N-H氢与μ-氧氧之间的弱静电相互作用对N-去烷基化决速步骤的主要影响。独立合成的双(μ-羟基)二铜(II)配合物[Cu2(OH)2(Et3CY)2](CF3SO3)2（10）、[Cu2(OH)2(iBu3CY)2](CF3SO3)2（11）和[Cu2(OH)2(Bn3CY)2](ClO4)2（12）的X射线晶体结构表明，Cu(III)2(μ-O)2核中的N-H与μ-氧之间的有效相互作用可能增强了金属-氧物种的氧化能力。