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Accession number;04A0258603
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| Title;Negative Temperature Dependence of Co-C Bond Cleavage Rates of a Vitamin B12 Model Complex. |
| Author;
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Journal Title;Abstracts. Symposium on Biofunctional Chemistry
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Journal Code:L0836A
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ISSN:
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VOL.18th;NO.;PAGE.40-41(2003)
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| Figure&Table&Reference;FIG.2 |
| Pub. Country;Japan |
| Language;Japanese |
| Abstract;Rates of cobalt(IV)-carbon bond cleavage of ([(DH)2CoIV(Me)(py)]+, DH=dimethylglyoxime, py=pyridine) produced by the one-electron oxidation of (DH)2CoIII(Me)(py) with Fe(bpy)33+ (bpy=2,2'-bipyridine) are significantly accelerated by the addition of pyridine derivatives in MeCN. The activation enthalpy (.DELTA.H.NEQ.obs) for the bimolecular bond cleavage reaction with pyridine derivatives decreases with increasing electron donor ability of pyridine derivatives to afford a negative .DELTA.H.NEQ.obs value (-40 kJ mol-1) in the case of 2,6-dimethoxypyridine. Such a negative temperature effect is a clear indication of the charge-transfer (CT) complex formed between [(DH)2CoIV(Me)(py)]+ and the pyridine derivatives acting as an actual intermediate for the cobalt(IV)-carbon bond cleavage. The formation of CT complexes was confirmed by observation of the CT bands during the cobalt(IV)-carbon bond cleavage of [(DH)2CoIV(Me)(py)]+ with pyridine derivatives. The stablization of the CT intermediate results in a significant decrease in the .DELTA.H.NEQ.obs value for the cobalt(IV)-carbon bond cleavage to afford a negative .DELTA.H.NEQ.obs value in the case of 2,6-dimethoxypyridine. (author abst.) |
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