Structural Diversity and Properties of Coordination Complexes Based on Chiral Amino Acid-Derived Ligands

FLORENCIA DI SALVO; FEDERICO MOVILLA; ANDREA PAOLA RIVAS MARQUINA; JUAN MANUEL REY; OLGA C. SÁNCHEZ M.

Cartagena

Simposio; 7º Simposio Latinoamericano de Química de Coordinación y Organometálica; 2019

Amino acids are among the most readily available sources of enantiomerically pure chiral compounds. Due to presence of N- and O-donor functional groups, amino acids are excellent ligands for transition-metal acceptors. Alternatively, the possibility of derivatization establishes amino acids an even more powerful moiety to explore the synthesis of chiral transition-metal complexes. Among others, one of the most popular applications of chiral transition-metal complexes is their use as enantioselective catalysts. On the other hand, the mentioned functional groups together with others provided by the amino acid bone, are able to establish strong intermolecular interactions such as H-bonds, and thus make them and their derivatives suitable building blocks for the construction of very stable crystalline solid materials.In our group we explore the synthesis of chiral molecules through the reaction of amino acids with a wide variety of aldehydes and subsequent reduction. As mentioned, due to the presence of caboxylic/carboxylate and secondary amine groups, they can be also considered as excellent candidates to act as ligands in the synthesis of coordination compounds. What is more, the relative position of both functionalities makes them suitable as quelates. In this presentation we will show the results achieved for a family of derivatives obtained using the aldehyde piperonal and the amino acids L-Ala, L-Phe and L-Tyr. Depending on the synthesis conditions, ligand identity and the metal ion, it was possible to obtain coordination compounds showing different molecularity and properties. All of them were characterized by different spectroscopies and their molecular and supramolecular structures were studied based on single crystal X-ray diffraction experiments. For instance, for the L-Ala derivatives only mononuclear compounds where obtained, but for the ligands containing the L-Phe or L-Tyr, different coordination systems where observed. For the aromatic amino acids members, the structural flexibility, the presence of π-rings and the higher solubility in organic media make them more versatile and also, these characteristics could be the key of the different structural features and properties of the resulting coordination systems. A clear example can be seen in Fig. 1, where a trinuclear Ni(II)-carbonate complex constructed by the self-assembly of L-Tyr based ligands incorporating ambient CO2 as a central μ3-CO32? bridging unit is shown. Surprisingly, when the L-Tyr ligand is replaced by its L-Phe analogue, the resulting crystalline material corresponds to a mononuclear Ni(II) complex which does not show the property of the CO2 uptake.