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Notes: Base hydrolysis of optically pure mer-exo(H)- and mer-endo(H)-[CoCl(dien)(dapo)]2+ (A and B (X = Cl)), resp.; dien = N-(2-aminoethyl)ethane-1,2-damine; dapo = 1,3-diaminopopan-2-ol, kOH = (1.13 ±0.09)·105 M-1s-1 (A (X = Cl), kOH = (1.18 ± 0.11)·105M-1s-1 (B (X = Cl)); I = 1.0M (NaClO4 or NaN3)1, T = 298 K) is accompanied by retention of the mer-geometry and full racemization (99 ± 1%). It is shown this is not due to racemization of either reactants or products. This result, together with the fact that both A and B yield the same mer-exo(H)-product distribution, indicates the intermediacy of a pentacoordinate species II which is symmetrical (at least in the time average), viz. trigonal bipyramidal with a deprotonated (‘flat’) secondaryamine moiety. The H-exchange rates of the coordinated amine groups are consistent with this interpretation and indicate that loss of Cl- is the rate-determining step, in agreement with an SN1CB mechanism. The reactivity of the unsym-fac-exo(OH)- and unsy,-fac-endo(OH)-isomers C and D, respectively, is in sharp contrast: base hydrolysis is 3 orders of magnitue slower, and the reaction is accompanied by some change of coordination geometry (C, 23%; D, 10%, some inversion of configuration (C, 15%; D, 19%)); much lower acceleration of hydrolysis in base (106 vs. 1010). Azide competition during base hydrolysis of the mer-isomer A and B is quite large (R = [CoN3]∞/[CoOH]∞[N-3] = 1.4 ±0.2M-1, I= 1.0M, T = 298 K) and indicates that the coordinatively unsaturated intermediate II is highly selective. The ratios of exo(H)- and endo(H)-azide competition products A and B (X = N3), respectively, immediately after the substitution reaction (kinetic control) are independent of the engaged epierm A or B: 31.7 ± 0.9% of B (X = N3) and 68.3 ± 0.9% of A (X = N3, determined after ca. 10.t½ of the base hydrolysis). This is agreement with the effective site of deprotonation at the secondayr(central)-amine group of dien, cis to the leaving group X, and with a common set of intermediates. Epimerization of A and B (X = Cl, N3) is shown to proceed solely via the pentacoordinate (base hydrolysis) intermediate II, viz. the direct route involving a six-coordinate deprotonated intermediate is immeasurably slow. For the hydroxo products A and B (X = OH), the direct rotue may compete with the H2O-substitution(exchange) path which can occur by an internal conjugate-base process. The kinetically controlled distribution of complexes A/B (X = N3) is different from the quasi-thermodynamic one (19.1 ± 0.8% of B (X = N3) and 80.9 ± 0.8% of A (X = N3)). This is consistent with the differences in the base-hydrolysis rates of the reactants (kOh (A (X = N3))= (1.59 ± 0.04)·102M-1s-1; kOH (B (X = N3)) = (2.89 ± 0.22).102M-1s-1). Various aspects of the investigated reactions are discussed on the basis of the widely studied reaction of base hydrolysis of pentaaminecobalt(III) complexes. Also, the structure and reactivity of the pentacoordinate intermediate II are discussed in relation to various current models.

Notes: The two isomers of [Co(trap)2]3+ (meso-[Co(trap)2]3+ and rac-[Co(trap)2]3+; trap = 1,2,3-propanetriamine) have been studied by strain-energy minimization. The two isomers have been separated preparatively by fractional crystallization, and fully characterized by 13C-NMR and electronic spectroscopy, and microanalyses. The calculated isomer distribution (rac/meso = 60%: 40%) is in good agreement with HPLC analysis of thermodynamic equilibrium mixtures at 298 K and 353 K (rac/meso = 55% : 45%). These results are discussed in relation to the approach of calculating isomer distributions of hexaaminecobalt(III) systems by strain-energy minimization neglecting the differences in environmental effects.

Notes: Oxygentation of aqueous solutions of CoIII in presence of stoichiometric amounts of N-(2-aminoethyl)ethane-1,2-diamine (dien) and 1,3-diaminopropan-2-ol (dapo) produces μ-peroxocobalt(III) dimers. Acid cleavage (HCI) yields mer-exo(H)-, mer-endo (H)-, unsym-fac-exo(OH)-, and unsym-fac-endo(OH)-[CoCl(dien)(dapo)]2+ (A-D)(X = Cl), resp. and unsym-fac-[Co-(dien)(dapo-N,N′,O)]3+ (G). Isomer seperation was achieved by fractional crystallization as ZnCl42- and ClO4- salts and by ion-exchange chromatography. The corresponding bromo, azido, nitrito-O, nitro-N, thiocyanato, hydroxo, and aqua complexes were also synthesized. Optically resolved samples were prepared for chiral compounds, and the complexes were structurally characterized by X-ray analyses (\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\it \Lambda} \limits^ \to $\end{document}(-)436(CD)-A (X = N3)), (\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\it \Delta} \limits^ \to $\end{document}(-)436(CD)-B). (X = N3), \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\it \Delta} \limits^ \to $\end{document} (+)436(CD)-B by their chiroptical properties, and by 13C-NMR spectroscopy supported by 1H-NMR, IR, CD, and UV/VIS spectroscopy. \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\it \Lambda} \limits^ \to $\end{document}(-)436(CD)-mer-exo(H)-[Co(N3)(dien)(dapo)](hydrogen di-O-benzoyl-L-tartrate)2.4 H2O crystallizes in the orthorhombic space group P212121, a = 7.676(1) Å, b = 19.457(1) Å, c = 34.702(2) Å. \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\it \Lambda} \limits^ \to $\end{document}(-)436(CD)-mer-endo(H)-[Co(N3)(dien)(dapo)] (hydrogen di-O-benzoyl-L-tartrate)2.2.75 H2O crystallizes in the triclinic space group P1, a = 8.062(3) Å b = 10.296(1) Å, c = 15.056(2) Å, alpha = 80.55(1)°, β = 85.18(2)°, γ = 89.10(2)°. \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\it \Delta} \limits^ \to $\end{document}(+)436(CD)-mer-endo(H)-[Co(N3)(dien)(dapo)](hydrogen di-O-benzoyl-L-tartrate)2. 5.75 H2O crystallizes in the triclinic space group P1, a = 7.742(1) Å, b = 10.014(1) Å, c = 18.045(2) Å, α = 99.57(1)°, β = 92.87(1)°, γ = 102.56(1)°. The absolute configurations of the three cations were determined unambiguously. Interconversions of the various isomers and derivatives and structural, configurational, and spectroscopic aspects are discussed in detail.

Notes: Azide anation and racemization of optically pure mer-exo(H)- and mer-endo(H)-[Co(OH)(dien)(dapo)]2+ (A and B (X = OH), resp.; dien = N-(2-aminoethyl)ethane-1,2-diamine; dapo = 1,3-diaminopropan-2-ol) involve the same symmetrical pentacoordinate intermediate as the base hydrolyses of the corresponding mer-exo(H)- and mer-endo(H)-[CoX(dien)(dapo)]2+ species A and B, respectively, where X = Cl, Br, or N3. The kinetic parameters of the anation process are fully compatible with the independently measured competition ratio. The rate data reveal that substitution of OH- is unexpectedly fast, viz. it is not consistent with the usual sequence Br- 〉 Cl- 〉 H2O 〉 N3- 〉 OH-. This behavior is interpreted on the basis of an internal conjugate base mechanism which involves an amino-hydroxo/aminato-aqua tautomerism, viz. the reaction is actually an OH- -catalyzed substitution of [CoH2O(dien)(dapo)]3+ where deprotonation occurs effectively at the secondary-amine site NH of dien.

Notes: The template reaction of {bis[(S)-2-(aminomethyl)pyrrolidine]}copper(II) with formaldehyde, nitroethane, and base in MeOH yields optically pure {1,7-bis[(S)-pyrrolidin-2-yl]-4-methyl-4-nitro-2,6-diazaheptane}- copper(II) ([Cu((S,S)-mnppm)]2+) in high yield. The same reaction with rac-2-(aminomethyl)pyrrolidine is also described. Preparative details and spectroscopic and electrochemical properties of the CuII complexes and of the free ligands are reported and compared with structural, spectroscopic and electrochemical data of the CuII complex of the unsubstituted parent ligand 1,7-bis[(S)-pyrrolidin-2-yl]-2,6-diazaheptane (ppm). The crystal structure of [Cu(ppm)]Cl ClO4 has been determined by X-ray diffraction methods.

Notes: Butane- 1,2,4-triamine (trab) is the smallest tridentate aliphatic unsubstituted chiral triamine. With optically pure trab, there are three, with racemic trab five isomers of [Co(trab)2]3+, One of the five isomers is centrosymmetrical, the others are chiral. For one of the isomers, there are four possible conformations (all combinations of chair and skew boat conformations for the chelate six ring of each ligand), for the others there exist only three independent conformers. All sixteen independent structures have been calculated by strain-energy minimization. The calculated isomer distribution, based on total strain energies corrected with statistical entropy contributions (21%:16%:16%:4%:43%, and 40%:30%:30%, for racemic and optically pure trab, respectively) are in excellent agreement with the experimental data based on HPLC and 13C-NMR analyses of equilibrium solutions of the hexaamine-Co(III) compounds prepared by oxygenation of aqueous solutions in presence of activated charcoal. The results are also briefly discussed in relation to possible stereoselectivity upon complexation of optically pure trab and a racemic chiral ligand to a transition-metal center.

Notes: Chiral ligands coordinated to metal ions exert a selectivity towards the additional coordination of racemic substrates. Experimentally determined equilibria distributions of [Co(L3)2]3+ and [Co(L3)(L2)(X)]n+ are compared with calculated data based on strain-energy minimization (L3: trap = propane-1,2,3-triamine; 1,2,4-trab = butane-1,2,4-triamine; 1,2,3-trab = butane-1,2,3-triamine; 1,3,4-trpe = pentane-1,3,4-triamine; 1,3,4-tmeb = 2-methylbutane-1,3,4-triamine; 1,2,4-trpe = pentane-1,2,4-triamine; L2: en = ethane-1,2-diamine; pn = propane-1,2-diamine; X: NH3, OH2, OH-). Equilibration of Co(III) complexes was achieved by oxygenation of aqueous solutions of Co(II) salts in presence of the ligands. Quantitative isomer distribution was investigated with HPLC, and quantitative analysis of the enantiomeric excess (ee) of the racemic substrate (present in a two-fold excess) was studied, after chromatographical recovery, by 1H-NMR analysis of its Mosher-acid derivative. There is good agreement between calculated and experimental data. Systems with L = 1,2,4-trab are, as expected, relatively poorly discriminating (ee([Co(1,2,4-trab)2]3+) ∼ 5%; ee([Co(1,2,4-trab)(pn)(X)]n+) ∼ 10%). Calculations indicate that Me substitution of the ligand backbone of 1,2,4-trab (and trap) leads to an increased enantioselectivity (with practically constant isomer selectivity), and at the optimum site for substitution ∼ 90% ee is predicted.