Chiral Mn super(III)-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: Asymmetry; Catalysts; Catalytic activity; Derivatives; Infrared spectroscopy; Ligands; Single crystals; Synthesis (chemistry)
• 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(CH sub(3)COO) sub(2).4H sub(2)O followed by air oxidation to give (S,R)-Mn super(III)-salalen and -salan complexes in yields of 84-88%. The absolute configuration of (S,R)-Mn super(III)-salalen was determined by single-crystal X-ray diffraction and CD analysis of the ligands and complexes showed similiar Cotton effects. The Mn super(III)-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)p yrrolidin-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 degree C after 24 h. Chiral Mn super(III)-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.