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Facile cobalt(III) template synthesis of novel branched hexadentate polyamine monocarboxylates

Lookup NU author(s): Professor Bernard Golding

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Abstract

New hexadentate polyamine monocarboxylate ligands, 11-amino-9-(2- aminoethyl)-3,6,9-triazaundecanoate (tren-engly-), 12-amino-10-(2-aminoethyl)-3,7,10-triazadodecanoate (tren-tngly-) and 13-amino-11 (2-aminoethyl)-3,8,11-triazatridecanoate (tren-bngly-), were synthesized by intramolecular coupling of tetradentate tris(2-aminoethyl) amine (tren) and didentate N-(ω-formylalkyl)glycinates, OCH(CH 2)n,NHCH2CO2-, in easily and stereoselectively assembled cobalt(III) templates, p-[Co(tren){(RO) 2CH(CH2)nNHCH2CO2}] (O3SCF3)2, n= 1-3 (R = Me or Et). The reaction sequences comprised assembly of the template from [Co(tren)(O 3SCF3)2]O3SCF3 (1) and (RO)2CH(CH2)nNHCH2CO2Et, deprotection of the pendant acetal in acid, intramolecular condensation of the resulting aldehyde with a coordinated primary amine at intermediate pH to form the inline and reduction of this by NaBH4. For n = 1, imine formation occurred exclusively at the primary amine trans to the carboxylate producing the hexadentate 11-amino-9-(2-aminoethyl)-3,6,9-triazaundeca-5-enoato (tren-enimgly-) complex, i-[Co(trenenimgly)]Cl2̇3. 5H2O. In all instances, subsequent imine reduction gave the s isomer complex, exclusively. Complexes p-[Co(tren){(MeO)2CHCH 2gly}](O3SCF3)2 (3), i-[Co(tren-enimgly)]ZnCl4̇H2O (5), s-[Co(tren-engly)]ZnCl4 (s-6), s-[Co(tren-tngly)]ZnCl 4̇H2O (s-7) and s-[Co(tren-bngly)ZnCl 3]2ZnCl4 (s-8) were structurally characterized by X-ray crystallography. Charcoal-catalyzed equilibration of s-[Co(tren-engly)]Cl2̇2H2O dissolved in water produced the s- (s-6), p- (p-6) and t-[Co(tren-engly)]2+ (t-6) isomers in comparable amounts, p-6 and t-6 were also structurally characterized as their tetrachlorozincate and chloride salts, respectively. In base-catalyzed reactions, s-6 and t-6 each also formed p-6. Reduction of s-[Co(tren-engly)] Cl2̇2H2O with (NH4)2S and acidification liberated the pentaamino carboxylic acid ligand which was isolated as the hydrochloride salt.


Publication metadata

Author(s): Barfod R, Eriksen J, Golding BT, Hammershoi A, Jacobsen TA, Langkilde A, Larsen S, Monsted O, Sargeson AM, Sorensen HO

Publication type: Article

Publication status: Published

Journal: Dalton Transactions

Year: 2005

Issue: 3

Pages: 491-500

ISSN (print): 1477-9226

ISSN (electronic): 1477-9234

Publisher: Royal Society of Chemistry

URL: http://dx.doi.org/10.1039/b416994h

DOI: 10.1039/b416994h

PubMed id: 15672193


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