Paramagnetic solid-state NMR assignment and novel chemical conversion of the aldehyde group to dihydrogen ortho ester and hemiacetal moieties in copper(ii)- and cobalt(ii)-pyridinecarboxaldehyde complexes
Open Access
- 9 June 2021
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in RSC Advances
- Vol. 11 (33), 20216-20231
- https://doi.org/10.1039/d1ra02512k
Abstract
The complex chemical functionalization of aldehyde moieties in Cu(II)- and Co(II)-pyridinecarboxaldehyde complexes was studied. X-ray studies demonstrated that the aldehyde group (RCHO) of the four pyridine molecules is converted to dihydrogen ortho ester (RC(OCH3)(OH)2) and hemiacetal (RCH(OH)(OCH3)) moieties in both 4-pyridinecarboxaldehyde copper and cobalt complexes. In contrast, the aldehyde group is retained when the 3-pyridinecarboxaldehyde ligand is complexed with cobalt. In the different copper complexes, similar paramagnetic 1H resonance lines were obtained in the solid state; however, the connectivity with the carbon structure and the 1H vicinities were done with 2D 1H–13C HETCOR, 1H–1H SQ/DQ and proton spin diffusion (PSD) experiments. The strong paramagnetic effect exerted by the cobalt center prevented the observation of 13C NMR signals and chemical information could only be obtained from X-ray experiments. 2D PSD experiments in the solid state were useful for the proton assignments in both Cu(II) complexes. The combination of X-ray crystallography experiments with DFT calculations together with the experimental results obtained from EPR and solid-state NMR allowed the assignment of NMR signals in pyridinecarboxaldehyde ligands coordinated with copper ions. In cases where the crystallographic information was not available, as in the case of the 3-pyridinecarboxaldehyde Cu(II) complex, the combination of these techniques allowed not only the assignment of NMR signals but also the study of the functionalization of the substituent group.Funding Information
- Fondo para la Investigación Científica y Tecnológica (PICT 2016-1723, PICT 2019-845)
- Universidad de Buenos Aires (UBACyT 2018-2020/125BA, UBACyT 2020-2022/11BA)
- Consejo Nacional de Investigaciones Científicas y Técnicas (PIP 2014-2016/130)
- Secretaria de Ciencia y Tecnología - Universidad Nacional de Córdoba
- Ministerio de Ciencia, Innovación y Universidades (RTI2018-099668-BC22)
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