## 3 Results and Discussion  
In recent years, one of our main research lines has focused on the asymmetric synthesis of chiral amines by enantioselective addition of dialkylzinc reagents to _N_-(diphenylphosphinyl)imines using \(\beta\)-amino alcohols as ligands [47; 48; 49]. Since those ligands have shown to give excellent results in the ruthenium-catalyzed asymmetric transfer hydrogenation of ketones [12; 13; 14; 15; 16; 17; 18; 19] and _N_-sulfinylimines [38; 39; 40; 41] in isopropyl alcohol, we decided to investigate if they could also be applied to the reduction of _N_-phosphinyl legitimines by the same methodology. One of the most noteworthy chiral \(\beta\)-amino alcohols in the ATH of both ketones and _N_-sulfinyl imines is _cis_-1-amino-2-indanol [50]. Due to this, we chose (1\(S\),2_R_)-1-amino-2-indanol **L1** as a test ligand for the ruthenium-catalyzed transfer hydrogenation of the _N_-phosphinyl imine derived from acetophenone **1a** (Table 1). The ruthenium catalyst was prepared by refluxing a mixture of the ruthenium dimer [RuCl\({}_{2}\)(_p_-cymene)]\({}_{2}\) and **L1** in isopropyl alcohol. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Entry**} & \multirow{2}{*}{\begin{tabular}{c} **Ru-dimer** \\ **(mol\%)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **L1** \\ **(mol\%)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Base** \\ **Base** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **T (\({}^{\circ}\)C)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **t (h)** \\ \end{tabular} } & \multicolumn{2}{c}{**Product 2a**} \\ \cline{5-8}  & & & & **T (\({}^{\circ}\)C)** \\ \hline
1 & 5 & 20 & KOH & 50 & 25 & 5 & 56 & 66 \\
2 & 5 & 10 & KOH & 50 & 25 & 3 & 76 & 72 \\
3 & 5 & 5 & KOH & 50 & 25 & 6 & 55 & 64 \\
4 & 5 & 10 & KOH & 75 & 25 & 3 & 84 & 66 \\
5 & 5 & 10 & KOH & 25 & 25 & 6 & 78 & 66 \\
6 & 5 & 10 & LiOH & 50 & 25 & 5 & 63 & 70 \\
7 & 5 & 10 & NaOH & 50 & 25 & 3 & 55 & 68 \\
8 & 3 & 6 & KOH & 30 & 25 & 18 & 53 & 74 \\
9 & 5 & 10 & KOH & 50 & 50 & 2 & 74 & 60 \\
10 & 5 & 10 & KOH & 50 & 0 & 29 & 48 & 78 \\
11 \({}^{d}\) & 5 & 10 & KOH & 50 & 0 to 25 & 19 & 70 & 78 \\
12 \({}^{d}\) & 5 & 10 & KOH & 50 & \(-\)20 to 25 & 22 & 80 & 80 \\
13 \({}^{d}\) & 5 & 10 & _t_-BuOK & 50 & \(-\)20 to 25 & 20 & 87 & 82 \\
14 \({}^{d}\) & 5 & 10 & _t_-BuOK & 50 & \(-\)40 to 25 & 20 & 85 & 78 \\ \hline \hline \end{tabular}  
* The solution of the imine **1a** (0.5 mmol) in _i_-PrOH (9 mL) was added to a solution of the ruthenium catalyst [prepared by refluxing a mixture of [RuCl\({}_{2}\)(_p_-cymene)]\({}_{2}\) and amino alcohol **L1** in _i_-PrOH (2 mL)] at the temperature indicated. Then, the base (as a 0.1 M solution in _i_-PrOH) was added and the reaction mixture was stirred for the time indicated. \({}^{b}\) Isolated yield after purification by column chromatography (silica gel, hexane/acetone: 9/1) based on the starting imine **1a**. \({}^{c}\) Determined by HPLC using a ChiralCel OD-H column. The _R_-enantiomer was the major one in all cases. \({}^{d}\) The reaction mixture was stirred at the initial temperature for 1 h and then it was allowed to gradually reach room temperature.  
\end{table} 
Table 1: Ruthenium-catalyzed asymmetric transfer hydrogenation of _N_-(diphenylphosphinyl)---ketimine **1a** in isopropyl alcohol. Optimization of the reaction conditions \({}^{a}\). Since a proportion Ru-dimer:aminoalcohol:base = 1:4:10 is common for the ATH of ketones, we chose that proportion as the starting point of our study, using 5 mol% of the Ru-dimer. Under those conditions, the Ru complex bearing **L1** was able to reduce the imine **1a** in isopropyl alcohol in the presence of potassium hydroxide, affording product **2a** in a moderate yield and with 66% ee after stirring for 5 h at room temperature (Table 1, entry 1). This promising result encouraged us to try to optimize the reaction conditions.