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Multicomponent One‐pot Reactions Towards the Synthesis of Stereoisomers of Dipicolylamine Complexes
Author(s) -
Raje Sakthi,
Gurusamy Sureshbabu,
Koner Abhishek,
Mehrotra Sonam,
Jennifer Samson Jegan,
Vasudev Prema G.,
Butcher Ray J.,
Angamuthu Raja
Publication year - 2016
Publication title -
chemistry – an asian journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.18
H-Index - 106
eISSN - 1861-471X
pISSN - 1861-4728
DOI - 10.1002/asia.201500889
Subject(s) - chemistry , hemiaminal , trigonal bipyramidal molecular geometry , thioether , ethylenediamine , moiety , medicinal chemistry , stereochemistry , stereocenter , pyridine , nuclear magnetic resonance spectroscopy , crystallography , organic chemistry , crystal structure , catalysis , enantioselective synthesis
Reported are multi‐component one‐pot syntheses of chiral complexes [M(L R OR′)Cl 2 ] or [M(L R SR′)Cl 2 ] from the mixture of an N ‐substituted ethylenediamine, pyridine‐2‐carboxaldehyde, a primary alcohol or thiol and MCl 2 utilizing in‐situ formed cyclized Schiff bases where a C−O bond, two stereocenters, and three C−N bonds are formed (M=Zn, Cu, Ni, Cd; R=Et, Ph; R′=Me, Et, n Pr, n Bu). Tridentate ligands L R OR′ and L R SR′ comprise two chiral centers and a hemiaminal ether or hemiaminal thioether moiety on the dipicolylamine skeleton. Syn ‐[Zn(L Ph OMe)Cl 2 ] precipitates out readily from the reaction mixture as a major product whereas anti ‐[Zn(L Ph OMe)Cl 2 ] stays in solution as minor product. Both syn ‐[Zn(L Ph OMe)Cl 2 ] and anti ‐[Zn(L Ph OMe)Cl 2 ] were characterized using NMR spectroscopy and mass spectrometry. Solid‐state structures revealed that syn ‐[Zn(L Ph OMe)Cl 2 ] adopted a square pyramidal geometry while anti ‐[Zn(L Ph OMe)Cl 2 ] possesses a trigonal bipyramidal geometry around the Zn centers. The scope of this method was shown to be wide by varying the components of the dynamic coordination assembly, and the structures of the complexes isolated were confirmed by NMR spectroscopy, mass spectrometry, and X‐ray crystallography. Syn complexes were isolated as major products with Zn II and Cu II , and anti complexes were found to be major products with Ni II and Cd II . Hemiaminals and hemiaminal ethers are known to be unstable and are seldom observed as part of cyclic organic compounds or as coordinated ligands assembled around metals. It is now shown, with the support of experimental results, that linear hemiaminal ethers or thioethers can be assembled without the assistance of Lewis acidic metals in the multi‐component assembly, and a possible pathway of the formation of hemiaminal ethers has been proposed.