Oxidative and hydrolytic decomposition of a polyanionic chelating ligand

Article abstract of DOI:10.1021/ic00254a036

Osmium(IV) complexes of the polyanionic chelating (PAC) ligand 1,2-bis(3,5-dichloro-2-hydroxybenzamido)ethane (H₄CHBA-Et), coordinated as a tetradentate tetraanion, cannot be reversibly electrooxidized at room temperature. Electrooxidation of trans-Os(η⁴-CHBA-Et)(py)₂ in the presence of alcohols results in a sequence of oxidation and hydrolysis reactions involving the ethylene unit of the ligand, [η⁴-CHBA-Et]^4-. The sequence involves 15 observable species. The crystal structures of the species derived by dehydrogenation of the ethylene unit and subsequent oxidation of the C=C double bond to the trans 1-(methyl ether)-2-ol species are presented. The C-C bonds of the metallocyclopentane rings of this trans 1-(methyl ether)-2-ol species and a related trans-1,2-bis(methyl ether) analogue are cleaved in further steps to give two diastereomeric complexes (trans and cis (α-derived)) with N-formyl substituents. The formyl groups are sequentially hydrolyzed to give primary N-amido ligand complexes. The crystal structure of the trans-bis(primary N-amido) complex trans-Os(η²-CHBA)₂(t-Bupy)₂ (H₂CHBA = 3,5-dichloro-2-hydroxybenzamide) is reported. Evidence is presented for the mono- and diprotonation of the primary amido complexes.