Synthesis and Investigations of Chiral NNO Type Copper(II) Coordination Polymers

Herein, we report the synthesis and characterizations of chiral copper(II) coordination polymers (CPs) based on Schiff base of (S)-2-aminomethylpyrrolidine and salicylaldehyde derivatives. Single crystal X-ray analysis showed that copper(II) complex is 1D CP, with the repeating units LCu-OAc (L=ligand) organized in a perpendicular manner, where the copper(II) atoms are six-coordinated and have a distorted octahedral geometry. Also complex with chlorine counter ion having unusual dimeric structure was synthesized and characterized. It was demonstrated that CPs catalyze the enantioselective Henry reaction with up to 78% ee. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinhei

Synthesis and Investigations of Chiral NNO Type Copper(II) Coordination Polymers

Herein, we report the synthesis and characterizations of chiral copper(II) coordination polymers (CPs) based on Schiff base of (S)-2-aminomethylpyrrolidine and salicylaldehyde derivatives. Single crystal X-ray analysis showed that copper(II) complex is 1D CP, with the repeating units LCu-OAc (L=ligand) organized in a perpendicular manner, where the copper(II) atoms are six-coordinated and have a distorted octahedral geometry. Also complex with chlorine counter ion having unusual dimeric structure was synthesized and characterized. It was demonstrated that CPs catalyze the enantioselective Henry reaction with up to 78% ee. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinhei

Henry Reaction Revisited. Crucial Role of Water in an Asymmetric Henry Reaction Catalyzed by Chiral NNO-Type Copper(II) Complexes

Chiral copper(II) and cobalt(III) complexes (1-5 and 6, respectively) derived from Schiff bases of (S)-2-(aminomethyl)pyrrolidine and salicylaldehyde derivatives were employed in a mechanistic study of the Henry reaction-type condensation of nitromethane and o-nitrobenzaldehyde in CH2Cl2 (CD2Cl2), containing different amounts of water. The reaction kinetics was monitored by 1H and 13C NMR. The addition of water had a different influence on the activity of the two types of complexes, ranging from a crucial positive effect in the case of the copper(II) complex 2 to insignificant in the case of the stereochemically inert cobalt(III) complex 6. No experimental support was found by 1H NMR studies for the classical Lewis acid complexation of the carbonyl group of the aldehyde by the central copper(II) ion, and, moreover, density functional theory (DFT) calculations support the absence of such coordination. On the other hand, a very significant complexation was found for water, and it was supported by DFT calculations. In fact, we suggest that it is the Brønsted acidity of the water molecule coordinated to the metal ion that triggers the aldehyde activation. The rate-limiting step of the reaction was the removal of an α-proton from the nitromethane molecule, as supported by the observed kinetic isotope effect equaling 6.3 in the case of the copper complex 2. It was found by high-resolution mass spectrometry with electrospray ionization that the copper(II) complex 2 existed in CH2Cl2 in a dimeric form. The reaction had a second-order dependence on the catalyst concentration, which implicated two dimeric forms of the copper(II) complex 2 in the rate-limiting step. Furthermore, DFT calculations help to generate a plausible structure of the stereodetermining transition step of the condensation. © 2019 American Chemical Society