Stereoselectivity in the reduction of tris(oxalato)cobaltate(3-) by tris(ethylenediamine)cobalt(2+) and its derivatives

An X-ray investigation of stereoselectivity in the interactions of [Co(en)3]3+with [Co(ox)3]3−(en is ethane-1,2-diamine and ox is oxalate)

“…The reaction between the oxidant [Co(ox) 3 ] 3À and reductant [Co(en) 3 ] 2+ is an outer-sphere electron-transfer reaction in which modest chirality is induced in the [Co(en) 3 ] 3+ product when the oxidant is optically active (Marusak et al, 1989;Tatehata & Mitani, 1989; en is ethane-1,2-diamine and ox is oxalate). Attempts to understand the structural and electronic features that underlie the selectivity have centered on the patterns of hydrogen bonding between the reactants (Mitani et al, 2002).…”

“…Attempts to understand the structural and electronic features that underlie the selectivity have centered on the patterns of hydrogen bonding between the reactants (Mitani et al, 2002). Related solution studies pinpoint the C 3 -carboxylate face of [Co(ox) 3 ] 3À as an important motif in the chiral recognition of [Co(en) 3 ] 3+ (Marusak et al, 1989;Tatehata et al, 1981). The chiral discriminations are believed to result from differing helicities projected by the ligand arrangements along the principal axes of the tris-bidentate chelate.…”

Outer‐Sphere Redox Reactions Leading to the Formation of Discrete CoIII/FeII Pyrazine‐Bridged Mixed‐Valence Compounds

“…[8,11] These systems are a clear example of the importance of nonelectrostatic interactions in outer-sphere complex formation; they appear even between species with high charges of the same sign [12] that are able to tune the reactivity of {Oxd 1 ;Red 2 } species. [13][14][15] We have been involved in the kinetic and mechanistic study of the outer-sphere redox processes between [Fe II -(CN) 6 ] 4-(Scheme 1, Red 2 ) and Co III or Cr III complexes of pentadentate macrocyclic (N) 5 ligands (Scheme 1, Oxd 1 ). [10,[16][17][18] In these studies the careful tuning of both the reactants and reaction conditions has been possible, and the characterization of a large family of molecular di-, triand tetranuclear discrete mixed-valence (electron donor-acceptor) cyano-bridged Co III /Fe II and Cr III /Fe II has been accomplished.…”

“…The shift observed for the redox potential is of the same magnitude as that obtained for the analogous cyanide-bridged compounds, thus supporting the formation of a mixed-valence dinuclear Co III /Fe II complex with a {LCo III } unit attached to the iron centre. [17] The final solution of the reaction of any of the macrocyclic Co III complexes with [Fe II -(CN) 5 band, which appears at 452 nm (5000  -1 cm -1 ) for the mononuclear iron complex [33] and shifts to higher energies once the dinuclear complex is formed {[(transL 14 (Figure 2) of the MLCT and MMCT bands and the spectrum shifts to a maximum of approximately 420 nm (1900  -1 cm -1 ). Electrochemical experiments were also carried out on these solutions (after the addition of solid NaClO 4 to achieve I = 1.0 ).…”

“…UV/Vis spectral changes upon addition of S 2 2+ building blocks with an excess amount of pz under the same conditions does not produce any changes in the 1 H NMR spectrum of the sample, thereby indicating that the substitution of chloride by pyrazine under these conditions is negligibly slow, in accordance with the well-established inertness of this family of Co III macrocyclic complexes. [7,9] In this respect, the addition of free pz to an aqueous solution of the known [(L 14 All attempts to produce a solid sample from these solutions led to the formation of green-blue compounds due to the enhanced photochemical lability of the Fe III centre produced upon MMCT or MLCT excitation by visible light. [23,25,33] These undesired photodecomposition reactions have also been observed in cyanide-bridged Cr III analogous compounds described elsewhere.…”