Stable Five‐ and Six‐Coordinate Cobalt(III) Complexes with a Pentadentate Bispidine Ligand

Comba, Peter; Kerscher, Martin; Lawrance, Geoffrey A.; Martin, Bodo; Wadepohl, Hubert; Wunderlich, Steffen

doi:10.1002/anie.200800515

Cited by 26 publications

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“…The Zn(II) ion is hexacoordinated by ligand 1 5 and one chloride counterion (Figure ). As for other transition-metal complexes with pentadentate bispidone ligands − the coordination sphere can be described as an octahedral geometry with tetragonal distortion. As expected, the geometry of the rigid diazabicyclononane skeleton is only faintly modified upon coordination of Zn(II), and in particular the N1–N2 distance remains almost unchanged (Table ).…”

Section: Resultsmentioning

confidence: 99%

Kinetically Inert Bispidol-Based Cu(II) Chelate for Potential Application to ^64/67Cu Nuclear Medicine and Diagnosis

et al. 2015

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A family of 2,4-pyridyl-disubstituted bispidol derivatives bearing methylene carboxylic acid ethyl esters (L1-L3), methylene carboxylic acids (L4 and L5), or methylenethiophene (L6) groups were synthesized. In water, all ligands form rigid 1:1 complexes in the presence of Zn(II) in which the bicycle adopts a chair-chair conformation (cis isomer), as observed by (1)H NMR and, in the case of ligand L1, by an X-ray diffraction crystal structure. Interestingly, addition of Zn(II) ions on ligand L1 induces a metal-mediated selective hydrolysis of the ethyl esters. This selective hydrolysis was not observed upon addition of other cations such as Na(+), Mg(+), and Ca(2+). Reduction of the central ketone was achieved to prevent ring opening via retro Diels-Alder reactions and to afford highly stable and water-soluble ligands (L4, L5, L6). The complexation properties of L4 and L6 were studied in solution, with a particular interest for ligand L4. Fast complexation occurs in strongly acidic media (pH = 1), with a high affinity toward Cu(II) (log KCuL4 = 19.2(3), pCu = 17.0 at pH 7.4, pCu = -log[Cufree], [Cu] = 1 × 10(-6) M, [L] = 1 × 10(-5) M) and high selectivity versus Co(II), Ni(II), and Zn(II), as shown by the values of the binding constants obtained from potentiometric and spectrophotometric titrations. Reversible redox potential with E1/2 = -430 mV (vs normal hydrogen electrode) was measured. The complex was found to be fairly inert from acid-assisted dissociation experiments in 5 M HClO4 (t1/2 = 110 d at 25 °C).

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Section: Resultsmentioning

confidence: 99%

Kinetically Inert Bispidol-Based Cu(II) Chelate for Potential Application to ^64/67Cu Nuclear Medicine and Diagnosis

et al. 2015

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“…It appears that an elongation of chelate rings involving the dipyridylamine group might lead to the desired enforcement of pentagonal (bi)pyramidal structures, even for smaller metal ions, and this also emerges from similar effects observed with 6-vs. 5-membered chelate rings involving the N7-appended pyridine donor in L 1 -based pentadentate bispidine ligands. 46,47 Moreover, an expansion of the linker between N7 and the pyridine donors py3 and py4 would also lead to less distortion in the equatorial plane, even with relatively large metal-donor distances.…”

Section: Discussionmentioning

confidence: 99%

Synthesis and transition metal coordination chemistry of a novel hexadentate bispidine ligand

2015

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Reported is the new bispidine-derived hexadentate ligand (L = 3-(2-methylpyridyl)-7-(bis-2-methylpyridyl)-3,7-diazabicyclo[3.3.1]nonane) with two tertiary amine and four pyridine donor groups. This ligand can form heterodinuclear and mononuclear complexes and, in the mononuclear compounds discussed here, the ligand may coordinate as a pentadentate ligand, with one of the bispyridinemethane-based pyridine groups un- or semi-coordinated, or as a hexadentate ligand, leading to a pentagonal pyramidal coordination geometry or, with an additional monodentate ligand, to a heptacoordinate pentagonal bipyramidal structure. The solution and solid state data presented here indicate that, with the relatively small Cu(II) and high-spin Fe(II) ions the fourth pyridine group is only semi-coordinated for steric reasons and, with the larger high-spin Mn(II) ion genuine heptacoordination is observed but with a relatively large distortion in the pentagonal equatorial plane.

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“…In addition, octahedral Co(III) complexes are almost always LS. Co III complexes with nitrogen ligands are far from the spin-crossover point 61 (CoF 6 3À , 62 and a more recent nitrogen coordinated Co complex 63 are some of the rare notable HS Co III complexes). This indicates that the HS Co(III) state is not likely to be accessible as an intermediate.…”

Section: Reaction Mechanism Part 2: the Role Of The Spin-state Changementioning

confidence: 99%

Spin-forbidden hydrogen atom transfer reactions in a cobalt biimidazoline system

et al. 2012

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Stable Five‐ and Six‐Coordinate Cobalt(III) Complexes with a Pentadentate Bispidine Ligand

Cited by 26 publications

References 30 publications

Kinetically Inert Bispidol-Based Cu(II) Chelate for Potential Application to ^64/67Cu Nuclear Medicine and Diagnosis

Kinetically Inert Bispidol-Based Cu(II) Chelate for Potential Application to ^64/67Cu Nuclear Medicine and Diagnosis

Synthesis and transition metal coordination chemistry of a novel hexadentate bispidine ligand

Spin-forbidden hydrogen atom transfer reactions in a cobalt biimidazoline system

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Stable Five‐ and Six‐Coordinate Cobalt(III) Complexes with a Pentadentate Bispidine Ligand

Cited by 26 publications

References 30 publications

Kinetically Inert Bispidol-Based Cu(II) Chelate for Potential Application to 64/67Cu Nuclear Medicine and Diagnosis

Kinetically Inert Bispidol-Based Cu(II) Chelate for Potential Application to 64/67Cu Nuclear Medicine and Diagnosis

Synthesis and transition metal coordination chemistry of a novel hexadentate bispidine ligand

Spin-forbidden hydrogen atom transfer reactions in a cobalt biimidazoline system

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Product

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Kinetically Inert Bispidol-Based Cu(II) Chelate for Potential Application to ^64/67Cu Nuclear Medicine and Diagnosis

Kinetically Inert Bispidol-Based Cu(II) Chelate for Potential Application to ^64/67Cu Nuclear Medicine and Diagnosis