Role of the sulfonamide moiety of Ru(II) half-sandwich complexes in the asymmetric transfer hydrogenation of 3,4-dihydroisoquinolines
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The role of the sulfonamide moiety of Noyori-Ikariya [Ru(II)Cl(η 6-p-cymene)(S,S)-(N-arylsulfonyl-DPEN)] (where DPEN = 1,2-diphenylethylene-1,2-diamine) half-sandwich complexes in the asymmetric transfer hydrogenation (ATH) of imines (1-methyl-3,4-dihydroisoquinoline and 6,7-dimethoxy-1-methyl-3,4-dihydroisoquinoline) was investigated. Nine complexes were synthesized and characterized, most of which have not been previously reported and a majority of the corresponding ligands (N-arylsulfonyl-DPEN) have not been described in imine ATH. The study demonstrates that the structure of the sulfonamide fragment strongly affects the catalytic activity. By monitoring the reaction kinetics, it was found that the reactivity of certain complexes was moderately enhanced and the enantioselectivity was affected as well, albeit to a lesser extent. No simple structure–activity pattern was found, suggesting that extensive screening experiments are necessary in order to obtain the optimal catalyst for a particular substrate. The study complements other previously reported works on structure–activity relationships concerning Ru(II)-catalyzed ATH by adding a new dimension of investigation.
KeywordsRuthenium Asymmetric transfer hydrogenation Dihydroisoquinolines Sulfonamide
This work was financially supported by the Czech Science Foundation (P106/12/1276 and 15-08992S), grant for long-term conceptual development of the Institute of Microbiology of the Czech Academy of Sciences (RVO: 61388971) and the National Program of Sustainability (NPU I LO1215 and NPU I LO1509). The research was conducted within the infrastructure built up from the support of the Operational Program Prague—Competitiveness (projects CZ.2.16/3.1.00/22197, CZ.2.16/3.1.00/24501 and CZ.2.16/3.1.00/24023).