# Naphthalene-Based Polymers as Catalytic Supports for Suzuki Cross-Coupling
## 2 Results
### Suzuki Cross-Coupling  
All the synthesized catalysts were tested in a model reaction of Suzuki cross-coupling between BrAN and PBA under the following conditions: 1 mmol of BrAN, 1.5 mmol of PBA, 2.0 mmol of NaOH, 60 \({}^{\circ}\)C, 900 rpm, 0.2 mol.% of Pd. The results are presented in Table 2.  
As can be seen from Table 2, all initial (unreduced) samples revealed higher activity as compared with the reduced ones. This can be due to the known fact that Suzuki cross-coupling proceeds via the formation of homogeneous Pd species that are present in unreduced samples, while in the case of preliminarily reduced catalysts, the dissolution of Pd NPs into the reaction media should take place first (see, for example, our recent study [39]). The selectivity with respect to the cross-coupling products (MBP) was nearly the same for all the catalysts about 97-98% (see Figures 14b and 15b). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample** & **Conversion of BrAN, \%** & **Yield of MBP, \%** & \(R_{\rm o}\), mol\({}_{\rm BrAN}\)/(mol\({}_{\rm Pd}\)-min)** \\ \hline
1\%-Pd/NA60 & 96.3 & 90.7 & 89.2 \\
1\%-Pd/NA120 & 90.3 & 86.9 & 14.9 \\
1\%-Pd/NL60 & 92.3 & 88.5 & 41.1 \\
1\%-Pd/NNA120 & 97.7 & 93.4 & 77.0 \\
1\%-Pd/SNA120 & 95.6 & 91.6 & 64.0 \\ \hline
1\%-Pd/NA60-R & 74.5 & 72.7 & 9.3 \\
1\%-Pd/NA120-R & 80.8 & 79.1 & 12.6 \\
1\%-Pd/N/L60-R & 93.4 & 90.6 & 31.2 \\
1\%-Pd/NNA120-R & 69.6 & 67.9 & 10.7 \\
1\%-Pd/SNA120-R & 73.5 & 71.7 & 9.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Results of cross-coupling for the catalysts containing Pd supported on the synthesized NA-based polymers. Among the unreduced catalysts, the highest activity was found for 1%-Pd/NA60, 1%-Pd/NNA120, and 1%-Pd/SNA120 (Table 2, Figure 14a). In the case of reduced samples, the highest activity was found for 1%-Pd/NL60-R (Table 2, Figure 15a). For the catalyst 1%-Pd/SNA120, the reaction scope was studied at variations of aryl halides: 4-bromointrobenzene (BrNB), 4-bromoaminobenzene (BrAB), 4-bromobenzaldehyde (BrAL), and 4-bromotoluene (BrTL). The highest activity (209.2 mol\({}_{\text{BrAN}}\)/(mol\({}_{\text{Pd}}\)-min)) and selectivity (yield of cross-coupling product was >99%) were found in the case of BrNB (Figure S1, Table S1). Surprisingly, for the preliminarily reduced catalysts, there was no correlation between the sizes of Pd NPs, polymers' porosity, and the observed catalytic behavior at the first use. To verify if the support hydrophilicity influences the catalyst stability, all catalysts were tested in the second reaction run (Figure 16). Figure 14: Dependence of BrAN conversion on time (**a**) and “selectivity” with respect to MBP vs. BrAN conversion (**b**) for the initial unreduced catalysts; reaction conditions: 1 mmol of BrAN, 1.5 mmol of \(\text{Pa}\), 2.0 mmol of NaOH, 60 \({}^{\circ}\)C, 900 rpm, 0.2 mol.% of Pd. Figure 15: Dependence of BrAN conversion on time (**a**) and “selectivity” with respect to MBP vs. BrAN conversion (**b**) for the reduced catalysts; reaction conditions: 1 mmol of BrAN, 1.5 mmol of \(\text{Pa}\), 2.0 mmol of NaOH, 60 \({}^{\circ}\)C, 900 rpm, 0.2 mol.% of Pd. As can be seen from Figure 16, the catalysts based on the nitrogen- and sulfur-containing polymers revealed better stability as compared with the pure NA-based and NL-based samples. Earlier [40], we proposed that the higher hydrophilicity of the polymer can be responsible for better catalyst stability. Thus, for the NA-based polymers, the following trend can be found: the higher the oxygen content, the higher the remaining activity at the second reaction run (see Figure 17). Note that the remaining activity was estimated as a ratio (in %) of BrAN conversion achieved at the second run by 60 min to the initial conversion presented in Table 2.  
In spite of the relatively higher stability of the nitrogen- and sulfur-containing polymers as compared with the other samples, one can see that the loss of activity is noticeable.