Oxorhenium phosphinophenolato complexes with model peptide fragments: Synthesis, characterization, and stability considerations

The synthesis and characterization of a series of mixed-ligand oxorhenium(V ) complexes containing the o-diphenylphosphinophenolato ligand (HL) and mod el peptide fragments acting as the tridentate coligand are reported. Thus, by reacting equimolar amounts of tiopronin, Gly-Gly, Gly-L-Phe, or glutathi one (GSH) peptides on the [(n-C4H9)(4)N] [ReOCl3(L)] precursor in refluxing MeCN/MeOH or aqueous:MeCN/MeOH mixtures, the following complexes were obta ined: ReO{[SC(CH3)CONCH2COO][L]}[(n-C4H9)(4)N], 1, ReO{[H2NCH2CONCH2-COO] [ L]}, 2, ReO{[H2NCH2CONCH(CH2C6H5) COO][L]}, 3, and ReO{[SCH2CH(NHCOCH2CH2CH NH2-COOH)CONCH2COO] [L]}Na, 4. The compounds are closed-shell 18-electron o xorhenium species adopting a distorted octahedral geometry, as demonstrated by classical spectroscopical methods including multinuclear NMR, X-ray dif fraction analyses for 1 and 2 are also reported. By comparative stability s tudies of complexes 1-3 against excess GSH it was shown that complex 3 cont aining the bulky C6H5CH2 substituent adjacent to the coordinated carboxylat e group of Phe is the most stable complex.