Copper(II) Complexes of Sulfonated Salan Ligands: Thermodynamic and Spectroscopic Features and Applications for Catalysis of the Henry Reaction

Szilvia Bunda; Nóra V May; Dóra Bonczidai-Kelemen; Antal Udvardy; H Y Vincent Ching; Kevin Nys; Mohammad Samanipour; Sabine Van Doorslaer; Ferenc Joó; Norbert Lihi

doi:10.1021/acs.inorgchem.1c01264

Copper(II) Complexes of Sulfonated Salan Ligands: Thermodynamic and Spectroscopic Features and Applications for Catalysis of the Henry Reaction

Inorg Chem. 2021 Aug 2;60(15):11259-11272. doi: 10.1021/acs.inorgchem.1c01264. Epub 2021 Jul 12.

Authors

Szilvia Bunda^{1

2}, Nóra V May³, Dóra Bonczidai-Kelemen^{2

4}, Antal Udvardy¹, H Y Vincent Ching⁵, Kevin Nys⁵, Mohammad Samanipour⁵, Sabine Van Doorslaer⁵, Ferenc Joó^{1

6}, Norbert Lihi^{4

6}

Affiliations

¹ Department of Physical Chemistry, University of Debrecen, Debrecen H-4032, Hungary.
² Doctoral School of Chemistry, University of Debrecen, Debrecen H-4032, Hungary.
³ Centre for Structural Science, Research Centre for Natural Sciences, Budapest H-1519, Hungary.
⁴ Department of Inorganic and Analytical Chemistry, University of Debrecen, Debrecen H-4032, Hungary.
⁵ Department of Chemistry, University of Antwerp, Universiteitsplein 1, Antwerpen B-2610, Belgium.
⁶ MTA-DE Redox and Homogeneous Reaction Mechanisms Research Group, University of Debrecen, Debrecen H-4032, Hungary.

PMID: 34251196
DOI: 10.1021/acs.inorgchem.1c01264

Abstract

Copper(II) complexes formed with sulfonated salan ligands (HSS) have been synthesized, and their coordination chemistry has been characterized using pH-potentiometry and spectroscopic methods [UV-vis, electron paramagnetic resonance (EPR), and electron-electron double resonance (ELDOR)-detected NMR (EDNMR)] in aqueous solution. Several bridging moieties between the two salicylamine functions were introduced, e.g., ethyl (HSS), propyl (PrHSS), butyl (BuHSS), cyclohexyl (cis-CyHSS, trans-CyHSS), and diphenyl (dPhHSS). All of the investigated ligands feature excellent copper(II) binding ability via the formation of a (O^-,N,N,O^-) chelate system. The results indicated that the cyclohexyl moiety significantly enhances the stability of the copper(II) complexes. EPR studies revealed that the arrangement of the coordinated donor atoms is more symmetrical around the copper(II) center and similar for HSS, BuHSS, CyHSS, and dPhHSS, respectively, and a higher rhombicity of the g tensor was detected for PrHSS. The copper(II) complexes of the sulfosalan ligands were isolated in solid form also and showed moderate catalytic activity in the Henry (nitroaldol) reaction of aldehydes and nitromethane. The best yield for nitroaldol production was obtained for copper(II) complexes of PrHSS and BuHSS, although their metal binding ability is moderate compared to that of the cyclohexyl counterparts. However, these complexes possess larger spin density on the nitrogen nuclei than that for the other cases, which alters their catalytic activity.