Formation and Structure of a Cobalt(III) Complex Containing a Nonstabilized Pyridinium Ylide Ligand

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• 作者：Patrizia Siega ; Renata Dreos ; Giovanna Brancatelli ; Nicola Demitri ; Silvano Geremia
• 刊名：Organometallics
• 出版年：2014
• 出版时间：November 10, 2014
• 年：2014
• 卷：33
• 期：21
• 页码：6076-6080
• 全文大小：316K
• ISSN：1520-6041

文摘

The reaction of [Co^III(4,4鈥瞕msalen)(CH₂Cl)(S)], where 4,4鈥瞕msalen = 4,4鈥?dimethylsalen and S = solvent, with pyridine led to the formation of [Co^III(4,4鈥瞕msalen)(CH₂py)(Cl)], containing a nonstabilized pyridinium ylide as axial ligand. The complex has been unambiguously characterized by single-crystal X-ray diffraction analysis. Time-resolved ¹H NMR spectra showed that the formation of [Co^III(4,4鈥瞕msalen)(CH₂py)(Cl)] occurs in a two-step process involving a metallacyclized intermediate, cis-尾-[Co^III(4,4鈥瞕msalenCH₂)(py)(S)]⁺. A similar experiment carried out in the presence of different nitrogen bases having higher pK_a values (4-Me-py or 4-t-Bu-py) allowed a better separation of the two consecutive reactions. The almost complete conversion of [Co^III(4,4鈥瞕msalen)(CH₂Cl)(S)] in the cyclized intermediate before the formation of the ylide indicates that the ylide complex forms exclusively through the nucleophilic attack of the nitrogen base at the 鈭扖H₂O鈥?carbon of the cyclized species, whereas a parallel direct conversion through the displacement of Cl^{鈥?/sup> from the axial CH₂Cl group of [CoIII(4,4鈥瞕msalen)(CH₂Cl)(S)] may be ruled out.}