Chiral MnIII-salalen and -salan Complexes Derived from (S)-Pyrrolidin-2-ylmethanamine and Their Catalytic Activity in the Asymmetric Strecker Reaction

• Published in: European journal of inorganic chemistry 2014-10, Vol.2014 (29), p.5077-5083
• Main Authors: Kumar, Pramod, Saravanan, S., Khan, Noor-ul Hasan, Hussain, Firasat, Singh, Surendra
• Format: Article
• Language: English
• Subjects: Asymmetric synthesis; Manganese; N,O ligands; O ligands; Strecker reaction
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.201402548

The salalen and salan ligands have been synthesized by the reactions of (S)‐pyrrolidin‐2‐ylmethanamine and salicylaldehyde derivatives. These ligands were treated with Mn(CH3COO)2·4H2O followed by air oxidation to give (S,R)‐MnIII–salalen and –salan complexes in yields of 84–88 %. The absolute configuration of (S,R)‐MnIII–salalen was determined by single‐crystal X‐ray diffraction and CD analysis of the ligands and complexes showed similiar Cotton effects. The MnIII–salalen and –salan complexes were screened for their catalytic activity in the asymmetric Strecker reaction. (S,R)‐2,4‐Di‐tert‐butyl‐6‐({[1‐(3,5‐di‐tert‐butyl‐2‐hydroxybenzyl)pyrrolidin‐2‐yl]methylimino}methyl)phenolatomanganese(III) chloride (5 mol‐%) was found to be a suitable catalyst for the asymmetric Strecker reaction of N‐(4‐methoxybenzylidene)diphenylmethanamine with ethyl cyanoformate, which gave 89 % yield and 55 % ee of 2‐(benzhydrylamino)‐2‐(4‐methoxyphenyl)acetonitrile at –15 °C after 24 h. Chiral MnIII–salalen and –salan complexes have been synthesized and used as a catalyst for the asymmetric Strecker reaction. These complexes were characterized by elemental analysis, FTIR and UV/Vis spectroscopy, exact mass determination and single‐crystal XRD. The catalyst 9a catalysed the Strecker reactions of a range of substrates with moderate enantioselectivity of the corresponding products.