Stability and kinetics of acid- and anion-assisted dissociation reactions of hexaamine macrobicyclic mercury(II) complexes

The H+- and Cl--assisted dissociation kinetics and the stabilities of the complexes [Hg(sar)](2+) and [Hg((NH2)(2)-sar)](2+) (sar = 3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane and (NH2)(2)-sar = 1,8-diamino-sar) were determined. The Hg2+ dissociation rates depend on both the proton and the chloride ion concentrations. H+ competes with the metal ion for dissociated amine groups, and Cl- competes with the amine for vacant coordination sites. The rate laws are complicated. For the [Hg(sar)](2+) system (0.1 less than or equal to [H+] less than or equal to 1.0 M, 0.01 less than or equal to [Cl-] less than or equal to 1.0 M, I = 2.0 M (NaO3SCF3), 25.0 degrees C) the observed rate law is upsilon(-Hg2+) = (a + b[Cl-])[H+][Hg(sar)(2+)]/(1 + c[Cl-]), with a = 35(3) M-1 s(-1), b = 2.9(4) x 10(3) M-2 s(-1), and c = 33(5) M-1. For the [Hg((NH3)(2)-sar)](4+) system (0.001 less than or equal to [H+] less than or equal to 1.0 M, 0.01 less than or equal to [Cl-] less than or equal to 1.0 M, I = 1.0 M (LiClO4), 25.0 degrees C) the observed rate law is upsilon(-Hg2+) = (a + b[H+] + c[H+](2))[Cl-][Hg((NH3)(2)-sar)(4+)])/((1 + d[Cl-])(1 + e[H+])), with a = 0.056(6) M-1 s(-1), b = 8(3) M-2 s(-1), c = 5(3) M-3 s(-1), d = 1.3(4) M-1, and e = 1.1(5) x 10(2) M-1. Intimate mechanisms for the dissociation reactions are proposed. Using iodide ion or sar ligand as competing ligands and the reported values for the stabilities of HeI3- and HgI42- the stability constants at 25.0 degrees C were determined for [Hg(sar)](2+) (10(28.1(1)) M-1), [Hg(sar)I](+) (10(29.1(1)) M-2), [Hg((NH2)(2)-sar)I](+) (10(28.5(1)) M-2), and [Hg(cyclam)I](+) (10(30.8(1)) M-2) (cyclam = 1,4,8,11-tetraazacyclotetradecane) with [OH-] = 0.1 M, I = 0.5 M (NaClO4) and for [Hg((NH2)(2)-sar)](2+) (10(26.4(3)) M-1) with [OD-] = 0.1 M, I = 0.1 M (NaOD)

THIONYL CHLORIDE OXIDATION OF CHELATED GLYCINATE IN BIS(1,2-ETHANEDIAMINE)GLYCINATOCOBALT(III) - SYNTHESES OF N,O-BOUND N-FORMYL OXAMATE AND THIOOXAMATE

Addition of Lambda (+)(589)-bis(1,2-ethanediamine)glycinatocobalt(III) bis(trifluoromethanesulfonate)trifluoromethanesulfonic acid, Lambda(+)(589)-[(en)(2)Co(GlyO)](O3SCF3)(2) . HO3SCF3, to a solution of SOCl2 in N,N-dimethylformamide (DMF) followed by hydrolysis resulted in oxidation and formylation of the glycinate ligand affording the derivative N-formyloxamato complex and elemental sulfur. The crystal structure and absolute configuration of the N-formyloxamato complex, Lambda(+)(578)-[(en)(2)Co(OOCCONCHO)]ClO4, was established by X-ray diffraction [orthorhombic, space group P2(1)2(1)2(1); a=7.871(2), b=8.311(2), c=21.307(4) Angstrom; V=1394 Angstrom(3) and Z=4]. Addition of SOCl2 to a solution of [(en)(2)Co(GlyO)](O3SCF3)(2) . HO3SCF3 in DMF followed by hydrolysis afforded the thiooxamato complex, [(en)(2)Co(OOCCSNH)]Cl and sulfate. Hydrolysis of the N-formyloxamato complex at ca. pH 11.5 gave the oxamato complex, [(en)(2)Co(OOCCONH)](+). This complex and the thiooxamato complex each generated the N-formyloxamato complex when added to a SOCl2/DMF solution. Proposals for the mechanisms of formation of the isolated products are discussed

OXIDATION OF THE BIS(1,2-ETHANEDIAMINE)(SARCOSINATO)COBALT(III) ION WITH THIONYL CHLORIDE

The oxidation of bis(1,2-ethanediamine)(sarcosinato)cobalt(III) ion with SOCl2 in dimethylformamide gave the N-methylthiooxamato complex as the final product. The results, along with others, implicate the acid chloride chelate, a sulfine, and the methyl thiooxamato chelate as intermediates en route. The thiooxamato sulfur atom retains a nucleophilic capability and adds readily to cyclohexene in the thionyl chloride-dmf reaction medium to give an unusual imido hydroxycyclohexane thioester complex. Various results, including those in this paper, indicate that the chelated acid chloride readily loses an alpha-carbon proton and the resulting carbanion captures SOCl+. Elimination of HCl yields the sulfine and further addition of SOCl+, eliminations, and rearrangement yield chelated thiooxamate, which reacts even further under the pseudo-Vilsmeier conditions to the N-methyloxamato chelate complex

Synthesis of 2-(nitromethyl)ornithine from ornithine mediated by cobalt(III).

Rac.-p-(tris(2-aminoethyl)amine-2-(nitromethyl)ornithine)cobalt(III) trichloride (2d) was obtained by a simple three-step procedure from ornithine using cobalt template chemistry. p-(Tris(2-aminoethyl)amine-ornithine)cobalt(III) trichloride (2a) was obtained from tris(2-aminoethyl)amine (tren) and (S)-ornithine in the presence of cobalt(II), which was oxidised to cobalt(III) during the reaction. Complex 2a was selectively oxidised with thionyl chloride-dimethyl formamide to p-(tris(2-aminoethyl)amine-dehydro-ornithine)cobalt(III) trichloride 2b. Complex 2c, in which reaction of thionyl chloride-dimethyl formamide has also occurred at the δ-amine of ornithine, was obtained at longer reaction times. Complex 2b reacted with nitromethane anion to give rac.-p-(tris(2-aminoethyl)amino-2-(nitromethyl)ornithine)cobalt(III) trichloride (2d). The amino acid rac.-2-(nitromethyl)ornithine (1b) was released by reducing complex 2d with aqueous ammonium sulfide. Complex 2d was expected to release 2-(nitromethyl)ornithine (1b) in hypoxic cells, where the amino acid could act as an inhibitor of ornithine decarboxylase. Preliminary data indicated that complex 2d was weakly cytotoxic in one cell type studied

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-(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