文摘
The reaction of [CoIII(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 [CoIII(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 [CoIII(4,4鈥瞕msalen)(CH2py)(Cl)] occurs in a two-step process involving a metallacyclized intermediate, cis-尾-[CoIII(4,4鈥瞕msalenCH2)(py)(S)]+. A similar experiment carried out in the presence of different nitrogen bases having higher pKa values (4-Me-py or 4-t-Bu-py) allowed a better separation of the two consecutive reactions. The almost complete conversion of [CoIII(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.