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

Crespi, Ayelén F.; Sánchez, Verónica M.; Vega, Daniel; Pérez, Ana L.; Brondino, Carlos D.; Linck, Yamila Garro; Hodgkinson, Paul; Rodríguez-Castellón, Enrique; Lázaro-Martínez, Juan M.

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.

Citation

Crespi, A. F., Sánchez, V. M., Vega, D., Pérez, A. L., Brondino, C. D., Linck, Y. G., Hodgkinson, P., Rodríguez-Castellón, E., & Lázaro-Martínez, J. M. (2021). 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. RSC Advances, 11(33), 20216-20231. https://doi.org/10.1039/d1ra02512k

• Journal Article Type: Article
• Acceptance Date: Jun 1, 2021
• Online Publication Date: Jun 9, 2021
• Publication Date: 2021
• Deposit Date: Sep 7, 2021
• Publicly Available Date: Sep 7, 2021
• Journal: RSC Advances
• Publisher: Royal Society of Chemistry
• Peer Reviewed: Peer Reviewed
• Volume: 11
• Issue: 33
• Pages: 20216-20231
• DOI: https://doi.org/10.1039/d1ra02512k
• Public URL: https://durham-repository.worktribe.com/output/1265259