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.
Synthesis and characterization of cobalt(III) complexes containing α-diamine and carbinolamine derived from α-aminomalonate and ethylenediamine
Kojima, Takahiko,Usui, Takeshi,Tanase, Tomoaki,Yashiro, Morio,Yoshikawa, Sadao,Kuroda, Reiko,Yano, Shigenobu,Hidai, Masanobu
, p. 446 - 450 (2008/10/08)
The α-aminomalonate anion (AM2-) undergoes a C-N bond formation reaction with trans-[CoCl2(en)2]+ (en = ethylenediamine) in the presence of triethylamine (Et3N) to produce α-diamine and carbinolamine complexes. The reaction in water under air gives the carbinolamine complex 3 predominantly whereas the reaction under N2 yields the α-diamine complex 2 preferentially. These complexes were characterized by absorption and 1H and 13C NMR spectroscopy and elemental analysis. The X-ray crystal structure of the α-diamine complex 2b ([Co(N-(2-aminoethyl)-α,α-diaminomalonato)(en)]Cl·0.5H 2O) has been determined: formula C7H17N5O4CoCl·0-5H 2O, space group P1 (triclinic); a = 13.196 (4) A?, b = 13.212 (5) A?, c = 7.259 (3) A?, α = 93.78 (3)°, β = 89.00 (3)°, γ = 92.80 (3)°, Z = 4, R = 0.056. The free OH group of the carbinolamine complex 3 ([Co(N-(2-amino-ethyl)-α-amino-α-hydroxymalonato)(en)]ClO 4·H2O) was confirmed by 1H NMR in DMSO-d6 with the addition of D2O. Of great interest is that the C-N bond formation reaction occurs on the sp3 carbon of the AM2- ion.
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 the reduction of [Co(ox)3]3- by [Co(en)3]2+ and its derivatives
Marusak, Rosemary A.,Osvath, Peter,Kemper, Margaret,Lappin, A. Graham
, p. 1542 - 1548 (2008/10/08)
The oxidation of cobalt(II) by [Co(ox)3]3- in 1,2-diaminoethane solutions proceeds by both inner-sphere and outer-sphere pathways leading to formation of [Co(en)2(ox)]+ and [Co(en)3]3+ with rate constants 3300 and 390 M-1 s-1, respectively, at 25.0°C and 0.10 M ionic strength. When optically active [Co(ox)3]3- is used, both pathways show stereoselectivity. In the inner-sphere pathway, stereoselectivity is small, 1.5% ΔΔ, a consequence of the separation of the reacting centers by the oxalate bridge. In the outer-sphere pathway, stereoselectivity is 9% ΔΔ. The effect on the stereoselectivity of varying the structure of the reductant for the series [Co(sep)]2+, [Co(sen)]2+, [Co(en)3]2+, [Co((±)-bn)3]2+, and [Co((±)-chxn)3]2+ has been investigated for this pathway. Outersphere stereoseiectivity has also been examined in the reactions of [Co(mal)3]3- with [Co(en)3]2+ and [Co((±)-chxn)3]2+. The stereoselectivity data are consistent with a mechanism in which the carboxylate faces of [Co(ox)3]3- or [Co(mal)3]3- are presented to various orientations of the reductants in strong precursor ion pairs and are dependent on the relative importance of hydrogen-bonding and electrostatic interactions between the complexes.
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.
Oxygen Exchange and Cleavage of the Glycinate Chelate 2+ in Strongly Alkaline Solution
Buckingham, David A.,Clark, Charles R.
, p. 133 - 138 (2007/10/02)
Cleavage of the carboxylate chelate 2+ has been studied in 0.75 mol dm-3 NaOH. 18O-tracer results are interpreted as 16percent C-O and 84percent Co-O bond fission, the products ultimately being +, Co(II), and glyO-.The major Co-O cleavage path is interpreted as an SN1 (CB) process leading to both recapture of carboxylate oxygen(50percent, kex=4.8 * 10-6 s-1) and capture of solvent leading to + (50percent).
Stereoselective electron-transfer reactions of (ethylenediaminetetraacetato)cobaltate(III), (propylenediaminetetraacetato)cobaltate(III), and (1,2-cyclohexanediaminetetraacetato)cobaltate(III) with tris(ethylenediamine)cobalt(II)
Geselowitz, Daniel A.,Hammersh?i, Anders,Taube, Henry
, p. 1842 - 1845 (2008/10/08)
The stereoselectivities of the electron-transfer reactions of [Co(edta)]-, [Co(pdta)]- (pdta = propylenediaminetetraacetate), and [Co(cdta)]- (cdta = 1,2-cyclohexanediaminetetraacetate) with [Co(en)3]2+ in aqueous solution and Me2SO ([en] = 0.3 M, [Co(III)] = [Co(II)] = 0.01 M) have been determined by studying the optical purity of the [Co(en)3]3+ product. In aqueous solution, the ratio of the rate constants of the Δ-Λ and Δ-Δ reactions, kΔΛ/kΔΔ, is 1.2 for all three reactions, and in Me2SO, the ratios are 2.0, 2.1, and 2.1, respectively. The rate constants of the reactions in aqueous solution ([en] = 1.6 M, [enHCl] = 0.10 M, μ = 1.00 M, 25°C) were found to be 5.2, 5.2, and 5.0 M-1 s-1, respectively. For the [Co(edta)]-/[Co(en)3]2+ reaction, the degree of stereoselectivity is strongly solvent dependent, with kΔΛ/kΔΔ increasing for the solvent series water 2SO -/[Co(en)3]2+ reaction was studied. As the ethylenediamine concentration is raised from 0.085 to 0.985 M, the second-order rate constant rises from 4.66 to 5.79 M-1 s-1. To account for the similarity in reactivity of the three oxidants with [Co(en)3]2+, a model is proposed for the orientation of the reactants in the activated complex in which the carboxylate groups of the oxidant face the reductant.
211. Ligand Substitution Reaction of Bis(ethylenediamine)glycinatocobalt(III) Complex with Ethylenediamine Catalyzed by the Photo-excited Tris(2,2'-bipyridine)ruthenium(II) Complex
Ishikawa, Masahiko,Okamoto, Ken-ichi,Hidaka, Jinsai,Einaga, Hisahiko
, p. 2015 - 2021 (2007/10/02)
Substitution reaction with ethylenediamine of coordinated glycinate ligand in bis(ethylenediamine)glycinatocobalt(III) complex has been studied in the presence of photo-excited tris(2,2'-bipyridine)ruthenium(II) complex in alkaline aqueous solution (buffe
Photochemical and thermal decomposition of (ΔΔ,ΛΛ)-(μ-hydroxo)(μ-peroxo) bis[bis(ethylenediamine)cobalt(III)] ions in basic aqueous solution
Kikkawa, Masahiro,Sasaki, Yoichi,Kawata, Satoshi,Hatakeyama, Yoshihiro,Ueno, Fumio B.,Saito, Kazuo
, p. 4096 - 4100 (2008/10/08)
The title ion in aqueous basic solution does not undergo deoxygenation in the dark, but it does on irradiation with ultraviolet light to give the photoinduced equilibration (Equation Presented) The quantum yield determined in the presence of excess EDTA is ca. 2.2 × 10-3 on irradiation at 366 nm at 5°C and is virtually independent of pH (8.1-10.4). The yield on irradiation at 515 nm at ca. 25°C is -6. The ligand(O2)-to-metal charge-transfer excited state is relevant to the deoxygenation reaction. Continuous irradiation leads to subsequent irreversible decomposition to give cobalt(III) species including [CoIII(en)2(H2O)2]3+. Such an irreversible decomposition is much slower in the dark (ca. 5 × 10-7 s-1 at 5°C, pH 8.9, and I = 0.1 M (NaClO4); 1 M = 1 mol dm-3).
