Intramolecular carbinolamine and imine formation with cobalt(III)-amine complexes. Synthesis, structure, and reactivity

“…250fold faster exchange at the methylene than at the methyl group. 18 In [Co(NH 3 ) 4 {NH 2 CH 2 C(=NH)CH 3 }](ClO 4 ) 3 , the imine is the most acidic group and in basic solution the overall charge of the complex ion would be 2+ due solely to the anticipated quantitative deprotonation at the imine N atom (pK a < 10). 19 to be larger due to the higher overall charge of this ion.…”

Section: Synthesis and Characterizationmentioning

confidence: 99%

First aminoacetone chelate: [Co(tren){NH2CH2C(O)CH3}]3+—a substrate binding and activation model for zinc(ii)-dependent 5-aminolaevulinic acid dehydratase

et al. 2007

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The complex p-[Co(tren){NH(2)CH(2)C(O)CH(3)}](ClO(4))(3).H(2)O was produced stereoselectively from [Co(tren)(O(3)SCF(3))(2)]O(3)SCF(3) () and 2-(aminomethyl)-2-methyl-1,3-dioxolane. The structure of was determined by X-ray crystallography. The complex is the first aminoacetone chelate to be reported and the first structurally characterized example of a non-conjugated ketone moiety coordinated to cobalt(iii). The robust complex was stable to aquation in strong acid and behaved as an acid with pK(a) = 4.99(1) indicative of a strong activation of the aminoacetone ligand towards deprotonation. The complex constitutes a structural model for a proposed substrate binding mode relevant for substrate activation of the zinc(ii)-dependent enzyme 5-aminolaevulinic acid dehydratase.

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“…15 Torr) in a Büchi rotary evaporator using a water aspirator and water bath (ca. (14), 118 (18), 116 (16), 86 (86) and 75 (100).…”

Section: Experimental Generalmentioning

confidence: 99%

“…Specifically, base-catalyzed intramolecular addition reactions of cobalt(III)-bound primary and secondary amines to carbonyl groups have been explored. 12,15- 23 For coordinated primary amines the initially formed aminal 18 may react further by eliminating water to form a N-bound imine provided this is stereochemically feasible so that the imine moiety can achieve near planarity. 16,22 Regio-and stereoselectivity may be invoked by appropriate choice of transoid ligands.…”

Section: Introductionmentioning

confidence: 99%

“…16,22 Regio-and stereoselectivity may be invoked by appropriate choice of transoid ligands. 18 Thus, intramolecular condensation of an amine and the pendant aldehyde in the [Co(tren)Cl(NH 2 CH 2 CHO)]2 + complex to form the imine complex [Co(tren-enim)Cl] 2+ (tren-enim = 1,8-diamino-6-(2aminoethyl)-3,6-diazaocta-2-ene) occurs regioselectively with the primary amine trans to the chloride ligand. 15 Proton exchange of an amine site trans to Cl is typically ≈100-fold faster than if trans to another amine ligand, and a carboxylato ligand provides a similar trans activation.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2005

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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.

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Intramolecular carbinolamine and imine formation with cobalt(III)-amine complexes. Synthesis, structure, and reactivity

Cited by 24 publications

References 2 publications

Intramolecular Reversible Addition Reactions to the C=O Group

Intramolecular Reversible Addition Reactions to the C=O Group

First aminoacetone chelate: [Co(tren){NH2CH2C(O)CH3}]3+—a substrate binding and activation model for zinc(ii)-dependent 5-aminolaevulinic acid dehydratase

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

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