16569-46-3Relevant articles and documents
Observation of radical intermediates for unusual C-N bond formation of α-aminomalonate to give an α-diamine linkage. ESR studies on electron transfer reactions in cobalt(III)-polyamine complexes
Kojima, Takahiko,Tsuchiya, Jun-Ichi,Nakashima, Satoru,Ohya-Nishiguchi, Hiroaki,Yano, Shigenobu,Hidai, Masanobu
, p. 2333 - 2340 (2008/10/08)
The reactions of α-aminomalonate anion (AM2-) with complexes trans-[CoIIICl2(N4)]+ (N4 = (en)2, 2,3,2-tet, 3,2,3-tet; en = ethylenediamine, 2,3,2-tet = 3,7-diaza-1,9-diaminononane, 3,2,3-tet = 4,7-diaza-1,10-diaminodecane) were investigated by spin trapping and low-temperature electron spin resonance (ESR) spectroscopy. In the thermal C-N bond formation between the α-carbon of AM2- and a coordinated amino group of polyamine ligands, pathways for oxidation of AM2- to an iminomalonato intermediate depend on polyamine systems. Spin-trap ESR spectroscopy showed that the oxidation of AM2- proceeds via the radical formation at the α-carbon in the en and 2,3,2-tet systems. In both systems, MeOH plays an indispensable role in the α-diamine formation. Especially in the en system, the radicalization of MeOH took place upon heating prior to that of AM2- accompanying electron transfer (ET) to give a d7 high-spin (S = 3/2) Co(II) species from a d6 low-spin Co(III) ion. This change of the spin state at the cobalt center is required when a Co(III) complex acts as an oxidant for AM2-. In contrast, in the 2,3,2-tet system, the Co(III) center was reduced upon heating toward a low spin (S = 1/2) Co(II) species which readily reacted with dioxygen in the air to give a CoIII-O2- complex. EHMO calculation suggested that the superoxo ligand can perform intramolecular deprotonation of the α-proton of AM2- ligand and ET can occur from the α-carbon of the AM2- ligand to the Co(III) center. In the 3,2,3-tet system, formation of a high-spin Co(II) species was observed like the en system under conditions where the α-diamine formation occurs via ET from AM2- to a Co(III) ion. For the oxidation of substrates by Co(III) complexes via ET, the change of the spin state at the cobalt center is important and it is controlled by the polyamine ligands.
Oxidation of chelated amino acids to imine derivatives with thionyl chloride
Hammersh?i, Anders,Hartshorn, Richard M.,Sargeson, Alan M.
, p. 4525 - 4530 (2008/10/08)
Various (α-amino acidato)cobalt(III) complexes have been treated with SOCl2 in DMF. Provided the amino acid side chain does not contain functionalities that react with SOCl2, the complex undergoes a facile oxidation to give the related α-imino acidato complex. A mechanism is proposed for these reactions.
Stereoselectivity in Electron-Transfer Reactions of Tris(ethylenediamine)cobalt(II) with Several Anionic Cobalt(III) Complexes
Tatehata, Akira,Mitani, Tsuyoshi
, p. 1167 - 1170 (2007/10/02)
The stereoselectivities in the electron-transfer reactions of 2+ with eight Δ anionic Co(III) complexes in aqueous solution have been determined by observing the enantiomeric excesses of the 3+ product.The results are compared with the ion-pairing stereoselectivity between 3+ and the anionic complexes.Even the Δ anionic complexes which form favorable pairs with Δ-3+ yielded the excesses of Λ-3+ product.
