- Chelate ring sequence effects on thermodynamic, kinetic and electron-transfer properties of copper(II/I) systems involving macrocyclic lisands with S4 and NS3 donor sets
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The kinetic behavior of electron-transfer reactions involving several copper(II/I) complexes has previously been attributed to a dual-pathway "square scheme" mechanism in which changes in the coordination geometry occur sequentially, rather than concertedly, with the electron-transfer step. In the case of 14-membered macrocyclic quadridentate ligand complexes studied to date, the major geometric change appears to be the inversion of two coordinated donor atoms during the overall electron-transfer process. However, the relative importance of these two inversions has been a matter of speculation. In the current investigation, a comparison is made of Cu(II/I) systems involving two pairs of ligands with S4 and NS3 donor sets: 1,4,8,11-tetrathiacyclotctradecane ([14]aneS4-a); 1,4,7,11-tetrathiacyclotetradecane ([14]aneS4-b); 1,4,8-trithia-11-azacyclotetradecane ([14]aneNS3-fl); and 1,7,11-trithia-4-azacyclotetradecane ([14]aneNS3-b). In each pair of ligands, isomer a has the common chelate ring size sequence 5,6,5,6 while isomer b has the sequence 5,5,6,6. A crystal structure for [CuII([14] aneNS3-&)(H2O)](ClO4)2 demonstrates that, when coordinated to Cu(II), the b isomers stabilize the relatively rare ligand conformation designated as conformer II in which one donor atom is oriented opposite to the other three relative to the plane of the macrocycle. This eliminates one of the donor atom inversion steps which normally occurs during Cu(II/I) electron transfer. The copper complexes formed with these a and b isomers are examined in terms of (i) their CuIIL and CuIL stability constants, (ii) their CuIIL formation and dissociation rate constants, (iii) their CuII/IL redox potentials and (iv) their apparent electron self-exchange rate constants. Of the two donor atom inversions which occur in the case of the a-isomer complexes, the specific donor atom inversion which is common to the b-isomer complexes is judged to exhibit the larger energy barrier. Thus, it is presumed to represent the rate-limiting process responsible for the onset of "gated" electron transfer in previous studies on a-isomer complexes. The Royal Society of Chemistry 2003.
- Galijasevic, Semira,Krylova, Ksenia,Koenigbauer, Michael J.,Jaeger, Gregory S.,Bushendorf, Jeffery D.,Heeg, Mary Jane,Ochrymowycz, Leo A.,Taschner, Michael J.,Rorabacher, David B.
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p. 1577 - 1586
(2007/10/03)
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- ipso-Substitution of a Sulphinyl or Sulphonyl Group Attached to Pyridine Rings and its Application for the Synthesis of Macrocycles
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A sulphinyl or sulphonyl group directly bound to the 2- or 4-position of a pyridine ring was readily displaced by several nucleophiles such as RO-, RS-, and CN- to afford the corresponding ipso-substitution products.Similarly, 2-halogeno-6-methylsulphinyl- or -methylsulphonyl-pyridines also react with nuclephiles to afford 2-halogeno-6-substituted pyridine derivatives.Thus, the leaving abilities of the leaving groups fall in the order RSO2 > RSO > Br ca.Cl >> RS (R = alkyl or benzyl).The ipso-substitution can be applied to the synthesis of 2,6-disubstituted pyridino macrocycles containing both carbon-oxygen and carbon-sulphur bridges, resulting in several new macrocycles in moderate yields.
- Furukawa, Naomichi,Ogawa, Satoshi,Kawai, Tsutomu,Oae, Shigeru
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p. 1839 - 1845
(2007/10/02)
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- THE SYNTHESIS AND PROPERTIES OF ANTIMONY-SULPHUR AND ANTIMONY-OXYGEN LIGANDS
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The synthesis and properties of a series of potentially bi-, tri- and tetra-dentate ligands containing various combinations of antimony and sulphur and antimony and oxygen donors, is described.Included are SbPhn(o-C6H4OMe)3-n (n = 0, 1, 2); SbMe2(o-C6H4OMe); SbPhn(o-C6H4SMe3)3-n (n = 0, 1, 2); SbMe2(o-C6H4SMe); MeS(CH2)3SbR2 (R = Me, Ph) and S(CH2CH2CH2SbPh2)2.Attempts to prepare ligands with dimethylene backbones including (R2SbCH2CH2)2S (R = Me, Ph) failed.The ligands were characterised by analysis, 1H NMR and mass spectra, and by the preparation of quaternary derivatives.
- Levason, William,Sheikh, Baharuddin
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