Intramolecular Condensation Reactions of S-Methylmethionine Coordinated to Cobalt(III)

Abstract

The sulfonium salt [(en)₂CoO₂CCH(NH₂)(CH₂)₂S(CH₃)₂]₃+ (en = ethane-1,2-diamine), prepared by methylation of the thioether group of N,O-coordinated methionine , undergoes a set of complex, intramolecular condensations, oxidations, and rearrangements in aqueous base to give a novel pentadentate cobalt(III) complex (c. 20%) of the 1,9-diamino-4-hydroxy-3,7-diazanonane-4-carboxylate ion ( dhnc ). Its structure has been determined by X-ray crystallographic analysis as trans(O,O)-[Co( dhnc )(OH₂)](ClO₄)₂.2H₂O. The crystals were monoclinic, space group P 2₁/c with a 9.053(2), b 29.437(7), c 7.661(1) Ǻ, β 106.63(1)°, and Z 4; 2383 data with I ≥ 3σ(I) were refined to conventional R factors of 0.046 and 0.060. Investigations concerning the mechanism for the formation of this complex are described.