Syntheses, Characterization, and Dioxygen Reactivities of Cu(I) Complexes with <i>cis</i>,<i>cis</i>-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.本研究合成了6种基于顺式,顺式-1,3,5-三氨基环己烷衍生物（R3CY，R为乙基(Et)、异丁基(iBu)和苄基(Bn)）的一价铜配合物，分别为[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）与[Cu(CO)(Bn3CY)]SbF6（6），旨在探究一价铜配合物高效催化氧化反应的性能。上述配合物通过元素分析、电化学测试、X射线晶体结构解析、电子吸收光谱、红外光谱、1H核磁共振波谱以及电喷雾电离(ESI)质谱完成了表征。配合物1~3和6的晶体结构，以及配合物4~6的一氧化碳(CO)伸缩振动频率(νCO)均证实，R3CY向Cu(I)原子提供电子云密度的能力优于此前报道的配体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 ℃的四氢呋喃(THF)或二氯甲烷(CH2Cl2)体系中，配合物1~3与氧气反应生成双(μ-氧桥)二铜(III)中间体7~9，该转化经电子吸收光谱与共振拉曼光谱验证。测得中间体7和8的Cu-O伸缩振动频率ν(Cu-O)：其中7的16O2标记产物为553、581 cm-1，18O2标记产物为547 cm-1；8的16O2标记产物为571 cm-1，18O2标记产物为544 cm-1，其振动能量低于已报道的同类双(μ-氧桥)配合物。在-90 ℃的THF溶剂中，配合物7~9的分解速率分别为2.78×10^-4 s^-1（7）、8.04×10^-4 s^-1（8）与3.80×10^-4 s^-1（9）；在CH2Cl2溶剂中，7和8的分解速率分别为5.62×10^-4 s^-1和1.62×10^-3 s^-1，且7~9在CH2Cl2中的热稳定性低于其在THF中的热稳定性。上述分解反应均遵循一级动力学规律；针对8和9开展的氢氘(H/D)同位素实验表明，N-脱烷基化反应是分解过程的决速步骤。另一方面，配合物7在THF中的分解反应会以THF作为外源性底物，将其氧化为2-羟基四氢呋喃和γ-丁内酯作为氧化产物。通过在-90 ℃下采用N-H/D位点标记开展动力学实验，对配合物8的N-脱烷基化反应进行详细研究，测得其动力学同位素效应为1.25，表明N-H氢原子与μ-氧桥氧原子之间的弱静电相互作用，是影响N-脱烷基化决速步的主要因素。作为双(μ-氧桥)二铜(III)中间体的最终产物，我们独立合成了双(μ-羟桥)二铜(II)配合物[Cu2(OH)2(Et3CY)2](CF3SO3)2（10）、[Cu2(OH)2(iBu3CY)2](CF3SO3)2（11）与[Cu2(OH)2(Bn3CY)2](ClO4)2（12），其X射线晶体结构显示，Cu(III)2(μ-O)2核心中N-H与μ-氧桥之间的有效相互作用，可增强金属氧物种的氧化能力。