New Copper(II) Coordination Compounds Assembled from Multifunctional Pyridine-Carboxylate Blocks: Synthesis, Structures, and Catalytic Activity in Cycloalkane Oxidation

Two new copper(II) coordination compounds, namely a 1D coordination polymer [Cu(µ-cpna)(phen)(H(2)O)](n) (1) and a discrete tetracopper(II) derivative [Cu(phen)(2)(H(2)O)](2)[Cu(2)(µ-Hdppa)(2)(Hdppa)(2)] (2), were hydrothermally synthesized from copper(II) chloride as a metal source, 5-(4-carboxyphenoxy)nicotinic acid (H(2)cpna) or 5-(3,4-dicarboxylphenyl)picolinic acid (H(3)dppa) as a principal building block, and 1,10-phenanthroline (phen) as a crystallization mediator. Compounds 1 and 2 were isolated as air-stable microcrystalline solids and fully characterized by elemental and thermogravimetric analyses, IR spectroscopy, powder and single-crystal X-ray diffraction. In the solid state, the structure of 1 discloses the linear interdigitated 1D coordination polymer chains with the 2C1 topology. The crystal structure of an ionic derivative 2 shows that the mono- and dicopper(II) units are extended into the intricate 1D hydrogen-bonded chains with the SP 1-periodic net (4,4)(0,2) topology. Thermal stability and catalytic properties of 1 and 2 were also investigated. In fact, both Cu derivatives act as efficient homogeneous catalysts (catalyst precursors) for the mild oxidation of cycloalkanes by hydrogen peroxide to give the corresponding alcohols and ketones; the substrate scope and the effects of type and amount of acid promoter as well as bond-, regio-, and stereo-selectivity features were investigated.