| Summary: | The mononuclear zinc(II) complex <i>cis</i>-[ZnL<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>] (<b>1</b>; L = 4-(pyridin-3-ylcarbamoyl)benzoate) was synthesized and characterized. By soaking crystals of <b>1</b> in a mixture of DMF-H<sub>2</sub>O solution containing a slight excess of Cu(NO<sub>3</sub>)<sub>2</sub> × 3H<sub>2</sub>O a transmetalation reaction occurred affording the related copper(II) complex <i>trans</i>-[CuL<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>] (<b>2</b>). The structures of the compounds were authenticated by single crystal X-ray diffraction revealing, apart from a change in the isomerism, an alteration in the relative orientation of the chelating carboxylate groups and of the pyridine moieties. H-bond interactions stabilize both geometries and expand them into two-dimensional (2D) networks. The transmetalation was confirmed by SEM–EDS analysis. Moreover, the thermodynamic feasibility of the transmetalation is demonstrated by density-functional theory (DFT) studies. The catalytic activities of <b>1</b> and <b>2</b> for the oxidation of styrene and for the nitroaldol (Henry) C-C coupling reaction were investigated. The copper(II) compound <b>2</b> acts as heterogeneous catalyst for the microwave-assisted oxidation of styrene with aqueous hydrogen peroxide, yielding selectively (>99%) benzaldehyde up to 66% of conversion and with a turnover frequency (TOF) of 132 h<sup>−1</sup>. The zinc(II) complex <b>1</b> is the most active catalyst (up to 87% yield) towards the nitroaldol (Henry) coupling reaction between benzaldehyde and nitro-methane or -ethane to afford the corresponding β-nitro alcohols. The reaction of benzaldehyde with nitroethane in the presence of <b>1</b> produced 2-nitro-1-phenylpropanol in the <i>syn</i> and the <i>anti</i> diastereoisomeric forms, with a considerable higher selectivity towards the former (66:34).
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