Design and synthesis of quasi-diastereomeric molecules with unchanging central, regenerating axial and switchable helical chirality via cleavage and formation of Ni(II)–O and Ni(II)–N coordination bonds
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Beilstein Journal of Organic Chemistry 8 : 1920-1928 (2012)
We describe herein the design and synthesis of asymmetric, pentadentate ligands, which are able to coordinate to Ni(II) cations leading to quasi-diastereomeric complexes displaying two new elements of chirality: stereogenic axis and helix along with configurational stabilization of the stereogenic center on the nitrogen. Due to the stereocongested structural characteristics of the corresponding Ni(II) complexes, the formation of quasi-diastereomeric products is highly stereoselective providing formation of only two, (R-a*,M-h*,R-c*) and (R-a*,P-h*,R-c*), out of the four possible stereochemical combinations. The reversible quasi-diastereomeric transformation between the products (R-a*,M-h*,R-c*) and (R-a*,P-h*,R-c*) occurs by intramolecular trans-coordination of Ni-NH and Ni-O bonds providing a basis for a chiral switch model.