Copper(II) Coordination Polymers Self-Assembled from Aminoalcohols and Pyromellitic Acid: Highly Active Precatalysts for the Mild Water-Promoted Oxidation of Alkanes

Three novel water-soluble 2D copper­(II)
coordination polymers[{Cu2(μ2-dmea)2(H2O)}2(μ4-pma)]n·4nH2O (1), [{Cu2(μ2-Hedea)2}2(μ4-pma)]n·4nH2O (2), and [{Cu­(bea)­(Hbea)}4(μ4-pma)]n·2nH2O (3)were generated by
an aqueous medium self-assembly method from copper­(II) nitrate, pyromellitic
acid (H4pma), and different aminoalcohols [N,N-dimethylethanolamine (Hdmea), N-ethyldiethanolamine (H2edea), and N-benzylethanolamine
(Hbea)]. Compounds 2 and 3 represent the
first coordination polymers derived from H2edea and Hbea.
All the products were characterized by infrared (IR), electron paramagnetic
resonance (EPR), and ultraviolet–visible light (UV-vis) spectroscopy,
electrospray ionization–mass spectroscopy (ESI-MS(±)),
thermogravimetric and elemental analysis, and single-crystal X-ray
diffraction (XRD), which revealed that their two-dimensional (2D)
metal–organic networks are composed of distinct dicopper­(II)
or monocopper­(II) aminoalcoholate units and μ4-pyromellitate
spacers. From the topological viewpoint, the underlying 2D nets of 1–3 can be classified as uninodal 4-connected
layers with the sql topology. The structures of 1 and 2 are further extended by multiple intermolecular
hydrogen bonds, resulting in three-dimensional (3D) hydrogen-bonded
networks with rare or unique topologies. The obtained compounds also
act as highly efficient precatalysts for the mild homogeneous oxidation,
by aqueous H2O2 in acidic MeCN/H2O medium, of various cycloalkanes to the corresponding alcohols and
ketones. Overall product yields up to 45% (based on cycloalkane) were
attained and the effects of various reaction parameters were investigated,
including the type of precatalyst and acid promoter, influence of
water, and substrate scope. Although water usually strongly inhibits
the alkane oxidations, a very pronounced promoting behavior of H2O was detected when using the precatalyst 1,
resulting in a 15-fold growth of an initial reaction rate in the cyclohexane
oxidation on increasing the amount of H2O from ∼4
M to 17 M in the reaction mixture, followed by a 2-fold product yield
growth.

三种新颖的水溶性二维铜（II）配位聚合物（分别为：[Cu2(μ2-dmea)2(H2O)}2(μ4-pma)]n·4nH2O（1）、[{Cu2(μ2-Hedea)2}2(μ4-pma)]n·4nH2O（2）和[{Cu­(bea)­(Hbea)}4(μ4-pma)]n·2nH2O（3））通过水溶液自组装方法由硝酸铜（II）、均苯四甲酸（H4pma）以及不同的氨基醇（N,N-二甲基乙醇胺（Hdmea）、N-乙基二乙醇胺（H2edea）和N-苄基乙醇胺（Hbea））合成。化合物2和3代表了首次由H2edea和Hbea衍生的配位聚合物。所有产物均通过红外光谱（IR）、电子顺磁共振（EPR）、紫外-可见光光谱（UV-vis）、电喷雾电离-质谱（ESI-MS(±)）、热重分析和元素分析以及单晶X射线衍射（XRD）进行了表征，揭示了它们二维（2D）金属-有机网络由独特的二铜（II）或单铜（II）氨基醇酸根单元和μ4-均苯四甲酸间隔基团组成。从拓扑学的角度来看，1-3的潜在二维网络可归类为无节点的4连通层，具有sql拓扑结构。1和2的结构进一步通过多个分子间氢键得以扩展，从而形成了具有稀有或独特拓扑结构的立体（3D）氢键网络。所获得的化合物还作为高效的前催化剂，在酸性MeCN/H2O介质中，通过水合过氧化氢对各种环烷烃进行温和的均相氧化，生成相应的醇和酮。总体产品收率高达45%（以环烷烃计），并研究了各种反应参数的影响，包括前催化剂和酸促进剂类型、水的影响以及底物范围。尽管水通常强烈抑制烷烃氧化，但在使用前催化剂1时，观察到水表现出显著的促进作用，当反应混合物中H2O的量从约4 M增加到17 M时，环己烷氧化的初始反应速率增长了15倍，随后产品收率增长了2倍。