## 2 Results and Discussion
### Ir-Catalyzed Symmetric Silane Reduction of Ketone Using PS-L3  
With the polymer-supported azolium salt PS-**L3** prepared, we investigated its potential as a chiral ligand precursor in the Ir-catalyzed asymmetric silane reduction of ketones under heterogeneous conditions. As mentioned in the Introduction section, the catalytic reduction of ketones with (EO)\({}_{2}\)MeSiH is efficiently promoted by the Ir(OMe)(cod)\({}_{2}\)/**L1** combined catalytic system under homogeneous conditions at room temperature (Figure 2b) [46]. Notably, we previously established the _pre-mixing_ reaction procedure for this Ir-catalyzed silane reduction reaction in these earlier studies [46]. Table 2 summarizes the representative results of evaluating of Ir complex precursors and base additives with PS-**L3** as the key chiral NHC ligand precursor. The reaction involved stirring catalytic amounts of [IrCl(cod)]\({}_{2}\) and PS-**L3**, in the presence of Ag\({}_{2}\)O, in THF for 3 h. Then, (EO)\({}_{2}\)MeSiH (4.5 equiv. with respect to the ketone) was added, and the resulting mixture was stirred at room temperature for 20 h, following the _pre-mixing_ reaction procedure. Subsequently, a mixture of acetophenone (**3**), K\({}_{2}\)CO\({}_{3}\), and MeOH was introduced, and the reduction reaction was performed at room temperature for 6 h. This catalytic process yielded (S)-1-phenyl-1-propanol ((S)-**4**) at a 68% yield with 74% ee (entry 1). It is noteworthy that a dark green solid (likely a polymer-supported NHC-Ir species) appeared in the solution during the silane reduction reaction. At this point, it is important to highlight that the benzimidazolium ring in PS-**L3**, acting as the NHC ligand precursor, is covalently bonded to the polystyrene resin particle (via a chemical, not physical, bond). This strong bond prevents the NHC-Ir species, formed during the catalytic reaction, from dissociating from the resin. Furthermore, it was observed that no reaction occurred between **3** and (EtO)\({}_{2}\)MeSiH when using [IrCl(cod)]\({}_{2}\) as the catalyst without PS-**L3**. These results strongly suggest that the solid phase contains the polymer-supported NHC-Ir species, and an asymmetric reduction reaction likely occurs between the liquid phase, \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Entry 1** & **Ir Precursor** & **Azolium** & **Base** & **Product** & **Yield [\%] 2** & **Ee [\%] 3** \\ \hline
1 & [IrCl(cod)]\({}_{2}\) & PS-**L3** & Ag\({}_{2}\)O & (S)-**4** & 68 & 74 \\
2 & [IrCl(cod)]\({}_{2}\) & PS-**L3** & none & (S)-**4** & 31 & 13 \\
3 & [IrCl(cod)]\({}_{2}\) & PS-**L3** & \({}^{t}\)BuOK 4 & (S)-**4** & 23 & 39 \\
4 & [IrCl(cod)]\({}_{2}\) & PS-**L3** & AgOAc 4 & (S)-**4** & 24 & 44 \\
5 & [IrCl(cod)]\({}_{2}\) & PS-**L3** & Ag\({}_{2}\)CO\({}_{3}\) & (S)-**4** & 58 & 68 \\
6 & [IrCl(cod)]\({}_{2}\) & PS-**L4** 5 & Ag\({}_{2}\)CO\({}_{3}\) & (R)-**4** & 52 & 75 \\
7 & [IrOMe(cod)]\({}_{2}\) 6 & PS-**L3** & none & (S)-**4** & 49 & 38 \\
8 & Ir(acac)(cod) 7 & PS-**L3** & none & (S)-**4** & 26 & 41 \\ \hline \end{tabular}
\end{table} 
Table 2: Ir-catalyzed symmetric reduction of **3** with (EtO)\({}_{2}\)MeSiH under heterogeneous conditions. which contains the reactants, and the surface of the solid-state catalyst. Therefore, the result shown in entry 1 represents the first example of a catalytic enantioselective reaction using a polymer-supported chiral NHC-Ir catalyst derived from Merrifield resin under heterogeneous conditions. The use of a silver base in the _pre-mixing_ reaction procedure is crucial. Without Ag\({}_{2}\)O, the reaction resulted in poor enantioselectivity (Table 2, entry 2). This base likely facilitates the deprotonation of the C\({}_{2}\) position of the azolium ring in PS-**L3**, as shown in Figure 2a [42; 43; 44]. We then evaluated various base additives (entries 3-5). A promising result was obtained when treating [IrCl(cod)\({}_{2}\)] with PS-**L3** in the presence of Ag\({}_{2}\)CO\({}_{3}\), yielding (\(S\))-**4** at a 58% yield with 68% ee (entry 5).