## Discussion
### Catalysis in Batch and in Flow
Despite the moderate swelling and lack of polyethylene side-chains, as in the TentaGel\({}^{\text{TM}}\)-based commercial ligand **P2**, the resin beads **P7** could be charged with Cu(I) or Cu(II) salts dissolved in either polar aprotic solvents or mixtures featuring a high volume fraction of protic solvents. Lastly, after reduction (when necessary) with sodium \(\upiota\)-ascorbate, the corresponding **P7**-Cu(I) materials were demonstrated to be competent catalysts for CuAAC reactions in media of widely different polarities (from CH\({}_{2}\)Cl\({}_{2}\) to nearly pure MeOH, see Table 1). Considering that all the CuAAC runs were carried out for 20 h at room temperature, the specific activity of the various **P7**-Cu(I) catalysts compares well with that described for **P2**-Cu(I) [17]. With the information above in hand, we could turn to the use of supported catalysts in the continuous-flow reactors. This was initially done for the MCFRs **M7**-Cu(OTf)\({}_{2}\), whose high specific surface area (\(S_{\text{BET}}\) = 473 m\({}^{2}\) g\({}^{-1}\)) was deemed advantageous for the intended catalytic applications in-flow. In this regard, it is worth noting that, especially with the 15 cm-long MFCRs, the flow-rate was limited to \(\phi\)\(\leq\) 50-100 \(\mu\)L min\({}^{-1}\) by the ensuing back-pressure. Moreover, the longer devices showed a tendency to occasionally clog. In spite of this, the ability to flush the various reactors with a syringe pump confirmed that the monolithic bodies obtained under the conditions described in this work were endowed with a sufficiently large fraction of connected macropores to support the convective flow of the liquid stream. Notwithstanding the limitations above, excellent results were obtained with properly reduced **M7**-Cu(OTf)\({}_{2}\). In fact, while phenylhydrazine or hydroquinone turned out to be essentially useless in this case (Table 2, entries 1 and 2), resorting to the use of sodium l-ascorbate caused the expected boost of catalytic activity. Such a reducing agent was employed both as a preliminary flush, in aqueous MeOH, and then at a very small [46], yet undetermined, saturating concentration, in the MeOH/THF (4:1) stream of the reactants. Under these conditions, quantitative consumption of the azide at the reactor outlet was obtained in a relatively long benchmark run (\(S\)/\(C\) = 67) at \(\phi\) = 1.5 mL h\({}^{-1}\) (Table 2, entry 3). Interestingly, the flow-rate adopted in the experiment corresponds to an average residence time (\(\tau\)) of the reactants in the catalytic monolith body (as estimated by pycnometry) of less than 50 min. Subsequent tests at higher flow-rates (Table 2, entries 4-6) led to a decrease of the conversion extent, with a trend that has an obvious relationship with the progressive shortening of \(\tau\) (Figure 3). This conclusion is further supported by a final experiment under the initial conditions (\(S\)/\(C\) = 77 and \(\phi\) = 1.5 mL h\({}^{-1}\); Table 2, entry 7), where the MCFR proved to still be capable of fully converting the azide substrate, in spite of its extended usage, up to a total (accumulated) turnover number of \(TTON\) = 188. Figure 3: Graphical representation of the relationship between the flow-rate (\(\phi\)), estimated residence time (\(\tau\)), and conversion degree (_Conv._ %) for the benchmark CuAAC reaction in the 10 cm-long MCFR (for the conditions see Table 2, entries 3–7). Similar results were obtained with the reactor packed with the crushed **M7**-Cu(OTf)\({}_{2}\) monolith. In this case, hydroquinone or phenylhydrazine (Table 2, entries 8 and 9) were less effective in activating the Cu(II) pre-catalyst than sodium l-ascorbate (Table 2, entry 10). However, even in the latter case, the benchmark CuAAC reaction was largely incomplete at the high flow-rate adopted in the run (57% conversion at \(\oplus\) = 6 mL h\({}^{-1}\)).