## 2 Results and Discussion
### Ir-Catalyzed Symmetric Silane Reduction of Ketone Using PS-L3
As mentioned earlier, PS-**L3** was synthesized using (\(S\))-leucinol as the starting material. The chiral NHC ligand precursor with the opposite configuration, PS-**L4**, was synthesized from (\(R\))-leucinol. The catalytic reduction of **3** with (EtO)\({}_{2}\)MeSiH, using [IrCl(cod)\({}_{2}\)] and PS-**L4**, resulted in (\(R\))-**4** at a yield of 52% and 75% ee (entry 6). Next, we investigated the use of [Ir(OMe)(cod)]\({}_{2}\) as an Ir complex precursor. Previously, we successfully developed the [Ir(OMe)(cod)]\({}_{2}\)/**L1** combined catalytic system under homogeneous conditions (Figure 2b) [45]. The OMe group in [Ir(OMe)(cod)]\({}_{2}\) acts as an internal base, facilitating deprotonation at the C\({}_{2}\) position of the azolium ring in **L1**, thereby forming a monodentate NHC-Ir complex [45]. However, unlike its reduction with [Ir(OMe)(cod)]\({}_{2}\) under homogeneous conditions, the reduction of **3** with (EtO)\({}_{2}\)MeSiH under heterogeneous conditions using the [Ir(OMe)(cod)]\({}_{2}\)/PS-**L3** catalytic system resulted in a lower product yield and stereoselectivity (Table 2, entry 7). The acetylacetonate (acac) moiety in Ir(acac)(cod) is also known to function as an internal base, facilitating the formation of NHC species through the deprotonation of the azolium ring [48; 49; 50]. However, the reduction of **3** with (EtO)\({}_{2}\)MeSiH using Ir(acac)(cod) as the Ir precursor resulted in the formation of (\(S\))-**4** with a poor yield (entry 8). Consequently, it can be concluded that the combination of [IrCl(cod)]\({}_{2}\) with PS-**L3** in the presence of an appropriate base, such as Ag\({}_{2}\)CO\({}_{3}\), is the most effective system for the asymmetric silane reduction of **3**. Table 3 summarizes the results of the enantioselective silane reduction of several ketones catalyzed by the [IrCl(cod)]\({}_{2}\)/PS-**L3** system. While optimization of the reaction conditions is still needed, these reactions provided corresponding optically active alcohols with moderate enantiomeric excess values (entries 1-8). Similarly to the asymmetric reduction of **3** with (EtO)\({}_{2}\)MeSiH, propiophenone (**5**) was reduced to (\(S\))-1-phenyl-1-propanol ((S)-**6**) at a 47% yield with 73% ee (entry 1). Relatively good results were observed in the reductions of butyrophenone (**7**) and 4\({}^{\prime}\)-chloropropophenone (**17**), which yielded (\(S\))-1-phenyl-1-butanol ((\(S\))-**8**) at a 68% yield with 66% ee and (\(S\))-1-(4-chlorophenyl)propan-1-ol ((\(S\))-**18**) at a 76% yield with 65% ee, respectively (entries 2 and 7). We previously demonstrated that ketones **7** and **17** could be reduced with satisfactory yields and stereoselectivities using the [Ir(OMe)(cod)]\({}_{2}\)/**L1** catalytic system under homogeneous conditions [45]. These results will be discussed further. Valerophenone (**7**), cyclohexyl phenyl ketone (**11**), 4\({}^{\prime}\)-butylacetophenone (**13**), and 2\({}^{\prime}\)-acetonaphthone (**19**) were reduced with lower product yields, likely due to steric factors (entries 3-5 and 8). The reduction of 3\({}^{\prime}\)-methoxyacetophenone (**15**) with (EtO)\({}_{2}\)MeSiH was efficiently promoted by the [IrCl(cod)]\({}_{2}\)/PS-**L3** catalytic system, yielding (\(S\))-1-(3-methoxyhenyl)ethanol ((\(S\))-**16**) with 65% ee (entry 6).