## 2 Cu, Cu2O, CuO, and CuX Nanoparticles and Nanocomposites
### Magnetically Recoverable Systems
Despite the fact that these dimensions do not appear much different from those estimated for the Fe\({}_{2}\)O\({}_{3}\)-CS support (10-15 nm), a uniform dispersion of copper on the surface of the nanocomposite was inferred at the SEM resolution level. Two-components CuAAC runs (Scheme 1) were preferentially carried out in CH\({}_{2}\)Cl\({}_{2}\), with 1.5 mol % of the catalyst, to afford good to excellent yields in 12 h at r.t. (77%-96%). A high yield was recorded also in the reaction of dimethyl acetylcholinesterase with phenyl azide (96% in 12 h), from which it was concluded that **21** was effective even for internal alkynes. In this respect it should be noted, however, that acetylenedicarboxylate esters are known to undergo the thermal Huisgen 1,3-dipolar cycloaddition reaction at rate not dissimilar to that demonstrated in the study under exam, or even faster [142]. On this ground, the catalytic role of the nanocomposite material in the specific reaction of such an internal acetylene appears therefore far less than obvious. Magnetic separation of the catalyst beads allowed their recycling with just a moderate reduction of efficiency along four consecutive runs (96% \(\rightarrow\) 91% yield). The occurrence of aggregation phenomena, as a possible cause of performance loss, and of catalytic activity in solution, due to leached specie,  
Figure 11: Preparation of CuNPs on super-paramagnetic supports with PEG or PVPh (**a**); L-glutamic acid (**b**); chitosan (**c**); and EDACell (**d**) stabilizing agents. were examined and ruled out by TEM microscopy and through a standard \"filtration experiment\" (Maitils' test) [143], respectively. An organic-inorganic hybrid material (Scheme 11d), consisting in a layer of ethylenediamine-functionalized cellulose (EDACell) adsorbed onto silica gel-coated Fe\({}_{3}\)O\({}_{4}\) particles, was recently employed by [PERSON] et al. as a novel support for CuAAC catalytic systems [144]. Reduction with NaBH\({}_{4}\) of the material loaded with CuCl\({}_{2}\) gave a dark solid **22** that, according to XRD and electron microscopy, contained metallic copper clusters uniformly dispersed on the surface of around one order of magnitude larger core-shell magnetic nanoparticles. The activity of the supported system was probed in the CuAAC reaction between acetylenes and aromatic azides, with the latter formed in situ by substitution with NaN\({}_{3}\) on the product of diazotisation of the corresponding aniline in HCl-H\({}_{2}\)O (1:1) (Scheme 2c). An initial optimization stage demonstrated good performance at r.t. with as little as 0.25 mol % of the copper catalyst. Therefore, the same conditions were applied to the CuAAC of different substrates, to afford uniformly good results in relatively short reaction time (92%-95% yield in 3.5-5 h). Despite the use of a strongly acidic reaction medium, filtration tests did not reveal any significant catalytic activity in the solution. In addition, the copper content of the solid recovered by magnetic separation proved almost identical to that of the pristine material and its recycling led to almost unchanged results in the course of six consecutive runs (96% \(\rightarrow\) 93% yield). In addition to hybrid (organic-inorganic) magnetic catalytic systems above, some progress with purely inorganic materials were reported also. These examples, mentioned here for the sake of completeness, include the use of commercially available copper ferrite (CuFe\({}_{2}\)O\({}_{4}\)) and Fe\({}_{3}\)O\({}_{4}\)@TiO\({}_{2}\)/Cu\({}_{2}\)O nanocomposites [145; 146].