Stereochemistry of Complexes of Multidentate Ligands. I. Isomers of the Dichloro-2,9-diamino-4,7-diazadecanecobalt(III) Ion

Abstract

The preparation of the ligand 2,9-diamino-4,7-diazadecane (to be referred to as /,/-«,a'-dimethyltriethylenetetramine) is reported. The cobalt(III) complex ion dichloro-Z,Z-a,a'-dimethyltriethylenetetraminecobalt(III) can exist in three possible geometric isomers. All three were prepared. The configurations of these isomers were assigned on the basis of n.m.r. data.

Molybdenum-Based Polyoxometalates as Highly Active and Selective Catalysts for the Epimerization of Aldoses

“…In 1970s, Bilik discovered that molybdates under acidic conditions can epimerize aldoses to a thermodynamic equilibrium of the two epimers within 3 h at 90 °C without the formation of the complementary 2-ketose. − However, in order for molybdate to catalyze aldose epimerization, suitable pH ranges are required for the formation of the active site, which is composed of dinuclear complexes of the molybdate . Ni 2+ complexes coordinated with ethylenediamine can also epimerize aldoses into their corresponding epimers (glucose to mannose) at a molar ratio of 45:55 in methanol, as reported by Yoshikawa and co-workers. − One of the challenges with this approach is that the catalytic system is fairly complex, involving interplay among many parameters such as the structure of the nickel complex, the diamine ligand, the configuration of the sugars, and the chirality of the diamine ligand. − Recent reports have shown that heterogeneous catalysts, such as zeolites with Lewis acid centers, can also be used as catalysts for the epimerization of aldoses in methanol and water. Bermejo-Deval et al showed that Sn-Beta is highly active toward the epimerization of glucose in methanol, but this system is significantly limited by the low solubility of sugars in methanol.…”

Kinetics and stereochemistry of the spontaneous and mercury(II)-catalyzed acid hydrolysis for the symmetrical cis isomer of the dichloro(1,8-diamino-3,6-dithiaoctane)cobalt(III) cation

“…x-c/'x-Dichloro( 1,8-diamino-3,6-dithiaoctane)cobalt(III) chloride was prepared by the method of Worrell and Busch. 3 The chloride salt was dissolved in water and NaClOa was added. The purple-blue [Co(eee)Ch]C104 which precipitated was collected by filtration, washed with cold water, acetone, and ether, and air-dried.…”

Correlations of Nuclear Magnetic Resonance and Optical Rotatory Dispersion Spectra for Establishing the Absolute Configurational Assignment of Cobalt(III)-Chelated Optically Active Triethylenetetramine Homolog-α-Amino Acid Adducts

“…It was only recently that a tetradentate molecule was shown to be stereoselective in its coordination. 6 The ligand, 2,9-diamino-4,7-diazadecane [called , -, '-dimethyltrien, to illustrate its analogy to triethylenetetramine (abbreviated trien)], has been shown to prefer the absolute configuration, D-ris-a.6•7 However, it also forms the L-cis-ß and trans isomers in small amounts.6•7 None of the isomers O-cis-ß or L-cis-a was observed. Discussions of the theoretical reasons behind this ligand's stereoselective coordination are to be found in ref 6 and 7. In this communication a correlation between the nuclear magnetic resonance (nmr) and optical rotatory dispersion (ORD) spectra of several amino acid adducts of d-cis-aand L-ri5-/3-[Co(L,L-a,a'-dimethyltrien)Cl2]+ ions is reported.…”