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Stepwise assembly of heterobimetallic complexes: synthesis, structure, and physical properties.

ABSTRACT: Bimetallic active sites are ubiquitous in metalloenzymes and have sparked investigations of synthetic models to aid in the establishment of structure-function relationship. We previously reported a series of discrete bimetallic complexes with [FeIII-(μ-OH)-MII] cores in which the ligand framework provides distinct binding sites for two metal centers. The formation of these complexes relied on a stepwise synthetic approach in which an FeIII-OH complex containing a sulfonamido tripodal ligand served as a synthon that promoted assembly. We have utilized this approach in the present study to produce a new series of bimetallic complexes with [FeIII-(μ-OH)-MII] cores (M = Ni, Cu, Zn) by using an ancillary ligand to the FeIII center that contains phosphinic amido groups. Assembly began with formation of an FeIII-OH that was subsequently used to bind the MII fragment that contained a triazacyclononane ligand. The series of bimetallic complexes were charactered structurally by X-ray diffraction methods, spectroscopically by absorption, vibrational, electron paramagnetic resonance spectroscopies, and electrochemically by cyclic voltammetry. A notable finding is that these new [FeIII-(μ-OH)-MII] complexes displayed significantly lower reduction potentials than their sulfonamido counterparts, which paves way for future studies on high valent bimetallic complexes in this scaffold.

SUBMITTER: Lee JL

PROVIDER: S-EPMC8418555 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:A series of novel organogermanium(IV) catecholates 1-9 of the general formula R'2Ge(Cat), where R' = Ph, Et, have been synthesized. Compounds were characterized by 1H, 13C NMR, IR spectroscopy, and elemental analysis. The molecular structures of 1-3, 6, and 8 in crystal state were established using single-crystal X-ray analysis. The complexes are tetracoordinate germanium(IV) compounds containing a dioxolene ligand in a dianion (catecholato) form. Electrochemical transformations of target germanium(IV) complexes have been studied by cyclic voltammetry. The electro-oxidation mechanism of complexes 1-5, 7, and 10 (the related complex Ph2Ge(3,5-Cat) where 3,5-Cat is 3,5-di-tert-butylcatecholate) involves the consecutive formation of mono- and dicationic derivatives containing the oxidized forms of redox-active ligands. The stability of the generated monocations depends both on the hydrocarbon groups at the germanium atom and on the substituents in the catecholate ring. Compounds 6, 8, and 9 are oxidized irreversibly under the electrochemical conditions with the formation of unstable complexes. The radical scavenging activity and antioxidant properties of new complexes were estimated in the reaction with DPPH radical, ABTS radical cation, and CUPRACTEAC assay. It has been found that compounds 8 and 9 with benzothiazole or phenol fragments are more active in DPPH test. The presence of electron-rich moieties in the catecholate ligand makes complexes 5 and 7-9 more reactive to ABTS radical cation. The value of CUPRACTEAC for organogermanium(IV) catecholates varies from 0.23 to 1.45. The effect of compounds 1-9 in the process of lipid peroxidation of rat liver (Wistar) homogenate was determined in vitro. It was found that most compounds are characterized by pronounced antioxidant activity. A feature of complexes 1, 3, and 5-9 is the intensification of the antioxidant action with the incubation time. In the presence of additives of complexes 3, 5, 6, and 8, an induction period was observed during the process of lipid peroxidation.

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Stepwise assembly of heterobimetallic complexes: synthesis, structure, and physical properties.

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