The Reactivity of Hexa(<i>N</i>‐methylideneimine)Co<sup>III</sup> Complexes towards Nucleophiles: Structure and Mechanism

Kuppert, Dirk; Comba, Peter; Hegetschweiler, Kaspar

doi:10.1002/ejic.200501120

Cited by 6 publications

(14 citation statements)

References 50 publications

(53 reference statements)

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“…[9,[23][24][25] A corresponding hexaamine structure with L e acting as a chelating hexaamine ligand was also observed in the crystal structures of 2, 3, 4, and 5 c (Figure 4 and Figure S2 in the Supporting Information). It is noteworthy that 5 c is the only example with an ob orientation of the diaminoethane unit; the other hexaamine complexes adopted a lel orientation.…”

Section: Resultsmentioning

confidence: 52%

“…The low amount of strain for the bis-type(ii) structure M6 is remarkable, since this type of coordination is not particularly favorable for the parent MA C H T U N G T R E N N U N G (taci) unit. [9,17] It is also noteworthy that a low-strain bis-typeA Table S1 in the Supporting Information) does not exist according to these calculations.…”

Section: Resultsmentioning

confidence: 96%

“…[19] Metal-nitrogen bond lengths are as expected. [9,24,25,28] [Cu(L e )] 2 + exhibited the usual tetragonally elongated 4 + 2 Jahn-Teller geometry. [29] In solution, the hexaamine structure of these complexes was retained as indicated by the UV/Vis parameters for [Co H NMR spectra exhibited six and eight resonances, [30] respectively, with two separate signals for the CH 2 hydrogen atoms of the ethylene bridge, indicating a chiral C 2 symmetry for the solution structure.…”

Section: Resultsmentioning

confidence: 98%

“…This type of intra-molecular hydrogen bond formation is well established for the type(ii) coordination mode. [9,17] Some of the counter anions are also involved as hydrogen acceptors in the hydrogen bonding networks. A complete overview of the explicit hydrogen bond interactions in 1-6 is given as supporting information (Table S3).…”

Section: Resultsmentioning

confidence: 99%

“…Co III complexes with a bis-taci-ligand have been prepared recently in our laboratory by a template method. [9] However, in these complexes, the two taci subunits were interlinked by N=CH À NH À CH 2 À NH or NH À CH 2 À CA C H T U N G T R E N N U N G (NH 2 )=N bridges, which are sensitive to hydrolysis as soon as the metal center is removed. Herein, we report on the synthesis of a stable ethylene-bridged bis-taci derivative L e , and on its complex formation with Na I , Ni II …”

Section: Introductionmentioning

confidence: 99%

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Chelation versus Binucleation: Metal Complex Formation with the Hexadentate all‐cis‐N¹,N²‐Bis(2,4,6‐trihydroxy‐3,5‐diaminocyclohexyl)ethane‐1,2‐diamine

Bartholomä¹,

Gisbrecht²,

Stucky³

et al. 2010

Chemistry A European J

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The hexadentate ligand all-cis-N(1),N(2)-bis(2,4,6-trihydroxy-3,5-diaminocyclohexyl)ethane-1,2-diamine (L(e)) was synthesized in five steps with an overall yield of 39% by using [Ni(taci)(2)]SO(4).4H(2)O as starting material (taci=1,3,5-triamino-1,3,5-trideoxy-cis-inositol). Crystal structures of [Na(0.5)(H(6)L(e))](BiCl(6))(2)Cl(0.5).4H(2)O (1), [Ni(L(e))]Cl(2).5H(2)O (2), [Cu(L(e))](ClO(4))(2).H(2)O (3), [Zn(L(e))]CO(3).7H(2)O (4), [Co(L(e))](ClO(4))(3) (5c), and [Ga(H(-2)L(e))]NO(3).2H(2)O (6) are reported. The Na complex 1 exhibited a chain structure with the Na(+) cations bonded to three hydroxy groups of one taci subunit of the fully protonated H(6)(L(e))(6+) ligand. In 2, 3, 4, and 5c, a mononuclear hexaamine coordination was found. In the Ga complex 6, a mononuclear hexadentate coordination was also observed, but the metal binding occurred through four amino groups and two alkoxo groups of the doubly deprotonated H(-2)(L(e))(2-). The steric strain within the molecular framework of various M(L(e)) isomers was analyzed by means of molecular mechanics calculations. The formation of complexes of L(e) with Mn(II), Cu(II), Zn(II), and Cd(II) was investigated in aqueous solution by using potentiometric and spectrophotometric titration experiments. Extended equilibrium systems comprising a large number of species were observed, such as [M(L(e))](2+), protonated complexes [MH(z)(L(e))](2+z) and oligonuclear aggregates. The pK(a) values of H(6)(L(e))(6+) (25 degrees C, mu=0.10 M) were found to be 2.99, 5.63, 6.72, 7.38, 8.37, and 9.07, and the determined formation constants (log beta) of [M(L(e))](2+) were 6.13(3) (Mn(II)), 20.11(2) (Cu(II)), 13.60(2) (Zn(II)), and 10.43(2) (Cd(II)). The redox potentials (vs. NHE) of the [M(L(e))](3+/2+) couples were elucidated for Co (-0.38 V) and Ni (+0.90 V) by cyclic voltammetry.

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Section: Resultsmentioning

confidence: 52%

Section: Resultsmentioning

confidence: 96%

Section: Resultsmentioning

confidence: 98%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Chelation versus Binucleation: Metal Complex Formation with the Hexadentate all‐cis‐N¹,N²‐Bis(2,4,6‐trihydroxy‐3,5‐diaminocyclohexyl)ethane‐1,2‐diamine

Bartholomä¹,

Gisbrecht²,

Stucky³

et al. 2010

Chemistry A European J

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Facially Coordinating Triamine Ligands with a Cyclic Backbone: Some Structure−Stability Correlations

et al. 2010

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Metal complex formation of the two cyclic triamines 6-methyl-1,4-diazepan-6-amine (MeL(a)) and all-cis-2,4,6-trimethylcyclohexane-1,3,5-triamine (Me(3)tach) was studied. The structure of the free ligands (H(x)MeL(a))(x+) and H(x)Me(3)tach(x+) (0 ≤ x ≤ 3) was investigated by pH-dependent NMR spectroscopy and X-ray diffraction experiments. The crystal structure of (H(2)Me(3)tach)(p-O(3)S-C(6)H(4)-CH(3))(2) showed a chair conformation with axial nitrogen atoms for the doubly protonated species. In contrast to a previous report, Me(3)tach was found to be a stronger base than the parent cis-cyclohexane-1,3,5-triamine (tach); pK(a)-values of H(3)Me(3)tach(3+) (25 °C, 0.1 M KCl): 5.2, 7.4, 11.2. The crystal structures of (H(3)MeL(a))(BiCl(6))·2H(2)O and (H(3)MeL(a))(ClO(4))Cl(2) exhibited two distinct twisted chair conformations of the seven membered diazepane ring. [Co(MeL(a))(2)](3+) (cis: 1(3+), trans: 2(3+)), trans-[Fe(MeL(a))(2)](3+) (3(3+)), [(MeL(a))ClCd(μ(2)-Cl)](2) (4), trans-[Cu(MeL(a))(2)](2+) (5(2+)), and [Cu(HMeL(a))Br(3)] (6) were characterized by single crystal X-ray analysis of 1(ClO(4))(3)·H(2)O, 2Br(3)·H(2)O, 3(ClO(4))(3)·0.8MeCN·0.2MeOH, 4, 5Br(2)·0.5MeOH, and 6·H(2)O. Formation constants and redox potentials of MeL(a) complexes were determined by potentiometric, spectrophotometric, and cyclovoltammetric measurements. The stability of [M(II)(MeL(a))](2+)-complexes is low. In comparison to the parent 1,4-diazepan-6-amine (L(a)), it is only slightly enhanced. In analogy to L(a), MeL(a) exhibited a pronounced tendency for forming protonated species such as [M(II)(HMeL(a))](3+) or [M(II)(MeL(a))(HMeL(a))](3+) (see 6 as an example). In contrast to MeL(a), Me(3)tach forms [M(II)L](2+) complexes (M = Cu, Zn) of very high stability, and the coordination behavior corresponds mainly to an "all-or-nothing" process. Molecular mechanics calculations showed that the low stability of L(a) and MeL(a) complexes is mainly due to a large amount of torsional strain within the pure chair conformation of the diazepane ring, required for tridentate coordination. This behavior is quite contrary to Me(3)tach and tacn (tacn =1,4,7-triazacyclononane), where the main portion of strain is already preformed in the free ligand, and the amount, generated upon complex formation, is comparably low.

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Formation and Base Hydrolysis of Oxidimethaneamine Bridges in Co^III–Amine Complexes

et al. 2013

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cis-[CoL2](3+) (1a(3+)), trans-[CoL2](3+) (2a(3+)), cis-[Co(MeL)2](3+) (1b(3+)), and trans-[Co(MeL)2](3+) (2b(3+)), L = 1,4-diazepan-6-amine (daza) and MeL = 6-methyl-1,4-diazepan-6-amine (Medaza), were allowed to react as templates in acetonitrile with paraformaldehyde and triethylamine. Several Co(III) complexes, where two adjacent amino groups of two ligand moieties are interlinked by an oxidimethaneamine bridge, were obtained. Connection of a primary with a secondary amino group (prim-sec bridging) was found to be predominant. The singly and doubly bridged daza- and Medaza-derivatives 7a(3+), 9a(3+) and 7b(3+), 9b(3+) were characterized by crystal-structure analysis. The bridging process resulted in a slight lengthening of the mean Co-N distance, a red shift of the A1g-T1g transition, and an increase of the Co(III)/Co(II) reduction potential. Several minor components, which could be only partially separated by chromatographic methods, were also formed. The daza-derivatives 6a(3+) (prim-prim bridged) and 10a(3+) (bidentate coordination of one daza frame) formed in small quantities. The Medaza derivatives 3b(3+) and 4b(3+) (trans configuration of the Medaza frames, with additional pending carbinolamino groups), and 8b(3+) (with a methylideneimino group) represent intermediates of the condensation process. Their structure was again corroborated by X-ray diffraction. All bridged species (6a(3+), 7a(3+), 7b(3+), 8b(3+), 9a(3+), 9b(3+), and 10a(3+)) exhibited exclusively a cis orientation of the two diazepane frames, even if the trans configured 2a(3+) or 2b(3+) were used as starting materials. Molecular mechanics calculations indicate that in the bridged species with a trans configuration steric strain is substantially more pronounced. In alkaline aqueous media, 9a(3+) and 9b(3+) revealed a complete degradation of the bridges whereby the original 1a(3+) and 1b(3+) reformed. The pseudo-first-order rate constant k(obs) of the degradation reaction was found to depend linearly on OH(-) concentration. The degradation of the first bridge is about 100 times faster than the degradation of the second. The mechanism of formation and degradation of such oxidimethaneamine bridges is discussed.

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The Reactivity of Hexa(N‐methylideneimine)Co^III Complexes towards Nucleophiles: Structure and Mechanism

Cited by 6 publications

References 50 publications

Chelation versus Binucleation: Metal Complex Formation with the Hexadentate all‐cis‐N¹,N²‐Bis(2,4,6‐trihydroxy‐3,5‐diaminocyclohexyl)ethane‐1,2‐diamine

Chelation versus Binucleation: Metal Complex Formation with the Hexadentate all‐cis‐N¹,N²‐Bis(2,4,6‐trihydroxy‐3,5‐diaminocyclohexyl)ethane‐1,2‐diamine

Facially Coordinating Triamine Ligands with a Cyclic Backbone: Some Structure−Stability Correlations

Formation and Base Hydrolysis of Oxidimethaneamine Bridges in Co^III–Amine Complexes

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The Reactivity of Hexa(N‐methylideneimine)CoIII Complexes towards Nucleophiles: Structure and Mechanism

Cited by 6 publications

References 50 publications

Chelation versus Binucleation: Metal Complex Formation with the Hexadentate all‐cis‐N1,N2‐Bis(2,4,6‐trihydroxy‐3,5‐diaminocyclohexyl)ethane‐1,2‐diamine

Chelation versus Binucleation: Metal Complex Formation with the Hexadentate all‐cis‐N1,N2‐Bis(2,4,6‐trihydroxy‐3,5‐diaminocyclohexyl)ethane‐1,2‐diamine

Facially Coordinating Triamine Ligands with a Cyclic Backbone: Some Structure−Stability Correlations

Formation and Base Hydrolysis of Oxidimethaneamine Bridges in CoIII–Amine Complexes

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The Reactivity of Hexa(N‐methylideneimine)Co^III Complexes towards Nucleophiles: Structure and Mechanism

Chelation versus Binucleation: Metal Complex Formation with the Hexadentate all‐cis‐N¹,N²‐Bis(2,4,6‐trihydroxy‐3,5‐diaminocyclohexyl)ethane‐1,2‐diamine

Chelation versus Binucleation: Metal Complex Formation with the Hexadentate all‐cis‐N¹,N²‐Bis(2,4,6‐trihydroxy‐3,5‐diaminocyclohexyl)ethane‐1,2‐diamine

Formation and Base Hydrolysis of Oxidimethaneamine Bridges in Co^III–Amine Complexes