Facile cobalt(III) template synthesis of novel branched hexadentate polyamine monocarboxylates.
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-([small omega]-formylalkyl)glycinates, OCH(CH2)nNHCH2CO2-, 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)(O3SCF3)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 imine 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(tren-enimgly)]Cl2.3.5H2O. In all instances, subsequent imine reduction gave the s isomer complex, exclusively. Complexes p-[Co(tren){(MeO)2CHCH2gly}](O3SCF3)2 (3), i-[Co(tren-enimgly)]ZnCl4.H2O (5), s-[Co(tren-engly)]ZnCl(4)(s-6), s-[Co(tren-tngly)]ZnCl4.H2O (s-7) and s-[Co(tren-bngly)ZnCl3]2ZnCl4 (s-8) were structurally characterized by X-ray crystallography. Charcoal-catalyzed equilibration of s-[Co(tren-engly)]Cl(2).2H(2)O 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)]Cl2.2H2O with (NH4)2S and acidification liberated the pentaamino carboxylic acid ligand which was isolated as the hydrochloride salt.
Barfod
Rasmus
R
Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen O, Denmark.
Eriksen
Jette
J
Golding
Bernard T
BT
Hammershøi
Anders
A
Jacobsen
Thomas Amos
TA
Langkilde
Annette
A
Larsen
Sine
S
Mønsted
Ole
O
Sargeson
Alan M
AM
Sørensen
Henning Osholm
HO
D000596:Amino Acids / Q000737:chemistry; D002264:Carboxylic Acids / Q000138:chemical synthesis* / Q000737:chemistry; D003035:Cobalt / Q000737:chemistry; D018360:Crystallography, X-Ray; D007700:Kinetics; D008968:Molecular Conformation; D011073:Polyamines / Q000138:chemical synthesis* / Q000737:chemistry; D013237:Stereoisomerism
D000596:Amino Acids; D002264:Carboxylic Acids; D011073:Polyamines; D003035:Cobalt