## Discussion
### Catalysis in Batch and in Flow  
Initial runs in batch, with the bead-type resin **P7** charged with CuCl, Cu(OTf)\({}_{2}\), or CuSO\({}_{4}\), confirmed that the supported complexes were competent catalysts (or pre-catalysts) for the CuAAC. In particular, a sample of **P7**-CuCl was able to provide \(\geq\)83% final conversion in a sequence of five benchmark reaction cycles in CH\({}_{2}\)Cl\({}_{2}\) (Table 1, entries 1-5), carried out with a progressive decrease of the catalyst loading from 10 to 2 mol% (calculated with respect to the initial copper content). In this regard, it is worth noting that, while the last three runs did not reach full conversion of the azide substrate, they did not evidence any appreciable drop of the activity of the supported complex. Because Cu(II) salts are inactive in CuAAC [3], **P7**-Cu(OTf)\({}_{2}\) and **P7**-CuSO\({}_{4}\) were subjected to reduction before testing. Considering its effectiveness in our previous work with nanostructured CuAAC catalysts [37], as well as for other Cu(I)-supported systems [35], the use of phenylhydrazine in CH\({}_{2}\)Cl\({}_{2}\) was initially selected for this purpose. Unfortunately, despite the apparently fast reduction of the supported Cu(II) sites (as judged from the fading of the azure color of **P7**-Cu(OTf)\({}_{2}\)), the resulting material displayed unsatisfactory activity (Table 1, entries 6 and 7). Given its successful use in the literature for the reduction of **P2**-CuCl\({}_{2}\) and **P2**-CuSO\({}_{4}\)[17], it came as a surprise to discover that hydroquinone in THF or MeOH was completely ineffective towards **P7**-Cu(OTf)\({}_{2}\). In this case, no change of the azure color of the resin beads was observed and the hydroquinone-treated material did not display any significant CuAAC activity (Table 1, entry 8). Much to our delight, switching to the use of sodium \(\upiota\)-ascorbate in aqueous MeOH eventually afforded excellent results in a row of four benchmark runs performed with reduced **P7**-Cu(OTf)\({}_{2}\) at _S/C_ = 20 or _S/C_ = 100 (Table 1, entries 9-12). Although, in this case, some loss of catalytic activity towards the end of the series is suggested by the conversion values at the intermediate reaction time of 2 h, such a trend did not preclude the full conversion of azide at the standard 20 h end time of each run. Sodium \(\upiota\)-ascorbate in MeOH was also effective for the reduction of **P7**-CuSO\({}_{4}\) and provided a supported system endowed with high catalytic activity in the benchmark reaction (Table 1, entry 13). Nevertheless, recovery of the supported catalyst by filtration and reuse for promoting the CuAAC between benzylazide and 1-hexylne resulted in a surprisingly sluggish reaction (Table 1, entry 14). Since control experiments ruled out major oxidative phenomena of Cu(I) or extensive metal leaching from the resin (vide infra), these findings prompted us to examine the CuAAC of propargyl alcohol and 1-hexylne in the presence of the soluble catalyst from the TBTA ligand **1** (Table 1, entries 15 and 16). As expected, both homogeneous-phase reactions proceeded at a higher rate than the corresponding heterogeneous-phase ones. At the same time, however, a marked influence of the alkyne structure was observed, even in this case, with 1-hexylne, which was found to react at least six times slower than propargyl alcohol. By taking into account some literature precedents [39; 45], it seems reasonable to conclude that the hydroxyl group in the latter substrate exerts an accelerating effect on the CuAAC reaction, possibly through metal-chelation or by the increase of the acidity of the acetylenic proton. Overall, the results in batch confirmed that the highly cross-linked polystyrene architecture of **P7** was fit for the preparation of TBTA-Cu(I)-supported catalytic systems for the CuAAC.