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Oxorhenium Phosphinophenolato Complexes with Model Peptide Fragments:  Synthesis, Characterization, and Stability Considerations

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journal contribution
posted on 21.10.2000, 00:00 by Berthold Nock, Theodosia Maina, Francesco Tisato, Catherine P. Raptopoulou, Aris Terzis, Efstratios Chiotellis
The synthesis and characterization of a series of mixed-ligand oxorhenium(V) complexes containing the o-diphenylphosphinophenolato ligand (HL) and model peptide fragments acting as the tridentate coligand are reported. Thus, by reacting equimolar amounts of tiopronin, Gly-Gly, Gly-l-Phe, or glutathione (GSH) peptides on the [(n-C4H9)4N][ReOCl3(L)] precursor in refluxing MeCN/MeOH or aqueous MeCN/MeOH mixtures, the following complexes were obtained:  ReO{[SC(CH3)CONCH2COO][L]}[(n-C4H9)4N], 1, ReO{[H2NCH2CONCH2COO][L]}, 2, ReO{[H2NCH2CONCH(CH2C6H5)COO][L]}, 3, and ReO{[SCH2CH(NHCOCH2CH2CHNH2COOH)CONCH2COO][L]}Na, 4. The compounds are closed-shell 18-electron oxorhenium species adopting a distorted octahedral geometry, as demonstrated by classical spectroscopical methods including multinuclear NMR. X-ray diffraction analyses for 1 and 2 are also reported. By comparative stability studies of complexes 13 against excess GSH it was shown that complex 3 containing the bulky C6H5CH2 substituent adjacent to the coordinated carboxylate group of Phe is the most stable complex.