Mechanism for chiral recognition of a prochiral center and for asymmetric induction in asymmetric syntheses of .alpha.-amino acids using chiral cobalt(III) complexes. Crystal and molecular structures of (.alpha.-amino-.alpha.-methylmalonato)(4,6-dimethyl-1,9-diamino-3,7-diazanonane)cobalt perchlorate monohydrate and (.alpha.-amino-.alpha.-methylmalonato)(6,8-dimethyl-2,5,9,12-tetraazatridecane)cobalt bromide trihydrate

1986 ◽  
Vol 25 (10) ◽  
pp. 1709-1715 ◽  
Author(s):  
Morio Yashiro ◽  
Masanobu Ajioka ◽  
Shigenobu Yano ◽  
Koshiro Toriumi ◽  
Tasuku Ito ◽  
...  
Keyword(s):  
Amino Acids ◽  
Chiral Recognition ◽  
Molecular Structures ◽  
Asymmetric Induction ◽  
Asymmetric Syntheses ◽  
Crystal And Molecular Structures

A Solvent-Dependent and Electrochemically Controlled Self-Assembling/Disassembling System

2003 ◽  
Vol 68 (9) ◽  
pp. 1647-1662 ◽  
Author(s):  
Valeria Amendola ◽  
Massimo Boiocchi ◽  
Yuri Diaz Fernandez ◽  
Carlo Mangano ◽  
Piersandro Pallavicini
Keyword(s):  
Equilibrium Mixture ◽  
Bidentate Ligand ◽  
Molecular Structures ◽  
The Self ◽  
Molar Ratio ◽  
Crystal And Molecular Structures ◽  
Self Assembling ◽  
Irreversible Oxidation ◽  
Irreversible Reduction ◽  
Metal Ligand

The bis-bidentate ligand R,S-1,2-diphenyl-N,N'-bis(2-quinolinemethylidene)ethane-1,2-diamine (ligand 4), containing two (iminomethyl)quinoline moieties separated by a cis-1,2-diphenylethylene spacer, forms stable complexes with both CuI and CuII. With CuII, the monomeric 1:1 complex [CuII(4)]2+ is obtained both in CH3CN and CH2Cl2. With CuI and overall 1:1 metal/ligand molar ratio, an equilibrium mixture is obtained in CH3CN, consisting of [CuI(4)2]+, [CuI2(4)2]2+ and [CuI2(4)(CH3CN)4]2+. The preponderant species is the two-metal one-ligand "open" complex [CuI2(4)(CH3CN)4]2+, in which each Cu+ cation is coordinated in a tetrahedral fashion by one (iminomethyl)quinoline unit and by two CH3CN molecules. Precipitation from the equilibrium mixture yields only crystals of [CuI2(4)(CH3CN)4](ClO4)2·2CH3CN, whose crystal and molecular structures have been determined. On the other hand, in the poorly coordinating CH2Cl2 solvent, only the dimeric helical [CuI2(4)2]2+ complex is obtained, when the overall metal/ligand 1:1 molar ratio is chosen. Addition of large quantities of acetonitrile to solutions of [CuI2(4)2]2+ in dichlorometane results in the formation of [CuI2(4)(CH3CN)4]2+, i.e. in the solvent-driven disassembling of the CuI helicate. While electrochemistry in CH3CN is poorly defined due to the presence of more than one CuI species, cyclic voltammetry experiments carried out in CH2Cl2 revealed a well defined behavior, with irreversible oxidation of [CuI2(4)2]2+ and irreversible reduction of [CuII(4)]2+ taking place at separate potentials (∆E ≈ 700 mV). Irreversibility and separation of the redox events are due to the self-assembling and disassembling processes following the reduction and oxidation, respectively.

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