Isomerization Mechanisms of a Labile Co(II) Octahedral Complex

Riblet, Fabrice; Novitchi, Ghénadie; Helm, Lothar; Gulea, Aurélian; Merbach, André E.

doi:10.2533/000942906777674769

Cited by 3 publications

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“…For the cobalt(II) and cobalt(III) octahedral complexes V and X with coordination number 6, the thermodynamic stability is also important as well as in the case of copper(II) complexes XXI-XXIV. In solutions, the most labile cobalt (II) complex V (Co 2 þ has the electronic configuration 3d 7 with an inner coordination sphere lifetime of the ligand 10 24 to 10 25 s) is more active in comparison with the inert cobalt(III) complex X (Co 3 þ has the electronic configuration 3d 6 with a lifetime 10 4 -10 5 s) [38,39].…”

Section: Antileukemia Activitymentioning

confidence: 99%

In vitro antileukemia, antibacterial and antifungal activities of some 3d metal complexes: Chemical synthesis and structure – activity relationships

Gulea

Poirier

Roy

et al. 2008

Journal of Enzyme Inhibition and Medicinal Chemistry

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The present paper describes the synthesis, characterization and in vitro biological evaluation screening of different classes (ammoniacates, dioximates, carboxylates, semi-and thiosemicarbazidates) of Co(II), Co(III), Cu(II), Ni(II), Mn(II), Zn(II) and Fe(III) complexes. Schiff bases were obtained from the reaction of some salicyl aldehydes with, respectively, furoylhydrazine, benzoylhydrazine, semicarbazide, thiosemicarbazide and S-methylthiosemicarbazide to give tridentate ligands containing ONO, ONS or ONN as donor atoms. The synthetic metal complexes are of various geometrical and electronic structures, thermodynamic and thermal stabilities, and magnetic and conductance properties. All complexes, except those of Cu, are octahedral. Some Cu, Co and Mn compounds have a dimeric or a polymeric structure. The composition and structure of complexes were analysed by elemental analysis, IR and 1 H NMR and 13 C NMR spectroscopies, and magnetochemical, thermoanalytical and molar conductance measurements. All ligands and metal complexes were tested as inhibitors of human leukemia (HL-60) cells growth, and the most potent, the Cu(II) complexes, have been also tested for their in vitro antibacterial and antifungal activities. Structure-activity relationships were carried out.

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Section: Antileukemia Activitymentioning

confidence: 99%

In vitro antileukemia, antibacterial and antifungal activities of some 3d metal complexes: Chemical synthesis and structure – activity relationships

Gulea

Poirier

Roy

et al. 2008

Journal of Enzyme Inhibition and Medicinal Chemistry

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“…They demonstrate the capability to exist in solution as a large number of isomers in fast isomeric and enantiomeric equilibria detectable by NMR. In two preliminary reports we have shown the richness of their structural isomerism and the strength of the NMR line-broadening technique to assign the interconversion mechanism between the five labile isomers of [Co(TTFA) 2 (CH 3 py) 2 ]. In this paper we start with a simple [Co(A-A) 2 (C-C)] tris -chelate with mixed symmetrical bidentate ligands and increase progressively the complexity, for example, the number of isomers, and finish with bis asymmetrical bidentate ligand − bis monodentate ligand [Co(A-B) 2 c 2 ] complexes (Figure ).…”

Section: Introductionmentioning

confidence: 99%

Isomerization Mechanisms of Stereolabile tris- and bis-Bidentate Octahedral Cobalt(II) Complexes: X-ray Structure and Variable Temperature and Pressure NMR Kinetic Investigations

et al. 2010

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The isomerization dynamics of five labile octahedral Co(II) compounds have been investigated by variable temperature and pressure (1)H and (19)F NMR spectroscopy in dichloromethane solution. The X-ray crystal structure of the two tris-chelates, [Co(HFA)(2)bpic] (1) and [Co(TTFA)(2)bpy] (2), show a distorted octahedral arrangement of the 4 oxygen and 2 nitrogen donor atoms, with bidentate ligand bite angles smaller than 90 degrees. On the other hand, in the three bis-chelates, trans(N)-[Co(HFA)(2)(CH(3)py)(2)](3), cis(N)-cis(CF(3))-trans(S)-[Co(TTFA)(2)(CH(3)py)(2)](4), and trans(N)-trans(CF(3))-[Co(TTFA)(2)(CF(3)py)(2)](5), the replacement of the bidentate nitrogen donor ligands by two monodentate Rpy ligands leads to relaxed structures with almost regular octahedral arrangements of the donor atoms (HFA = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionato anion; TTFA = 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionato anion; bpy = 2,2'-bipyridine; bpic = 4,4'-dimethyl-2,2'-bipyridine). In solution the five complexes are stereolabile and all possible isomers are formed: from one for 1 up to five for 4 and 5. All cis-N isomers form pairs of enantiomers, whereas the trans-N isomers are achiral. A solid state structure/isomerization mechanism/rate correlation has been established for the isomerization dynamics of these Co(II) tris- and bis-chelates. The two tris-chelate complexes 1 and 2, with a distorted octahedral solid state structure, show one and three isomers in solution and isomerize/tautomerize very rapidly according to Bailar twist mechanisms. The three bis-chelate complexes 3, 4, and 5, with a close to octahedral symmetry in the solid state, show two, five, and five isomers, respectively. They isomerize/tautomerize 3 orders of magnitude slower as the tris-chelates, by an intramolecular dissociative mechanism involving a ring-opening of an arm of a bidentate ligand to form a TBP intermediate with a dangling bidentate ligand. The results of this first systematic investigation of the isomerization mechanisms of highly labile Co(II) complexes are supported by the NMR observed exchange paths (up to five for complexes for 4 and 5), the variable temperature (185 to 312 K) and pressure (up to 200 MPa) activation parameters, and a detailed analysis of the solid state structures.

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Catalysis From a to Z

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Isomerization Mechanisms of a Labile Co(II) Octahedral Complex

Cited by 3 publications

References 4 publications

In vitro antileukemia, antibacterial and antifungal activities of some 3d metal complexes: Chemical synthesis and structure – activity relationships

In vitro antileukemia, antibacterial and antifungal activities of some 3d metal complexes: Chemical synthesis and structure – activity relationships

Isomerization Mechanisms of Stereolabile tris- and bis-Bidentate Octahedral Cobalt(II) Complexes: X-ray Structure and Variable Temperature and Pressure NMR Kinetic Investigations

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