Tosylated diamine ligands, chiral

Rhodium diphosphine catalysts can be easily prepared from [Rh(nbd)Cl]2 and a chiral diphosphine, and are suitable for the hydrogenation of imines and N-acyl hydrazones. However, with most imine substrates they exhibit lower activities than the analogous Ir catalysts. The most selective diphosphine ligand is bdppsuif, which is not easily available. Rh-duphos is very selective for the hydrogenation of N-acyl hydrazones and with TOFs up to 1000 h-1 would be active enough for a technical application. Rh-josiphos complexes are the catalysts of choice for the hydrogenation of phosphinyl imines. Recently developed (penta-methylcyclopentyl) Rh-tosylated diamine or amino alcohol complexes are active for the transfer hydrogenation for a variety of C = N functions, and can be an attractive alternative for specific applications. 

Chiral Nitrogen Donor Ligands (Amines and Oxazolines). 1,2-Diphenyl-ethylenediamine (DPEN (56)) and its alkylated and tosylated derivatives, as well as 1,2-cyclohexane-diamine (CHDA (57)) based ligands proved to be applicable in a range of asymmetric reactions (Fig. 7), especially in enantioselective transfer hydrogenations providing ees more than 90% for acetophenone as substrate. Crucial steps of this reaction are the irreversible deprotonation of the ligand... 

Asymmetric transfer hydrogenation of ketones in the presence of soluble transition metal catalysts has been developed [8-10], enantioselectivities up to 99% ee being obtained using a ruthenium catalyst bearing mono-N-tosylated diphenyl-ethylenediamine as a ligand. Iridium complexes associated with fluorous chiral diimines 3a-3c or diamines 4a—4b have also been shown to be effective catalysts in hydrogen-transfer reduction of ketones [11,12]. 

Simple chiral N-tosylated 1,3-diamines 42-45 were used in Ru(ll)-catalysed TH of acetophenone and other aryl ketones [65]. The highest ee obtained was 56 % with the ligand 42 bearing one chiral centre, while two chiral-centre ligands 44 and 45 were even less effective. A lower optical induction of 1,3-diamines when compared to 1,2-diamines could stem from better flexibility of the chelating ring of the Ru centre with 1,3-diamines, thus consequently enhancing the number of possible diastereomeric transition states with ketones. 

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