Inversion and proton exchange at chiral nitrogen centers of [Co(acac)2(Ph-en)]+ (acac=2,4-pentanedionate ion; Ph-en=N-PHENYLETHYLENEDIAMINE (cas 1664-40-0)) and [Co(acac)2(Me-en)]+ Me-en=N-methylethylenediamine)

Add time:09/09/2019    Source:sciencedirect.com

The rates of the base-catalyzed proton exchange and inversion (epimerization) at chiral nitrogen centers of [Co(acac)2(Ph-en)]+ (acac=2,4-pentanedionate ion; Ph-en=N-phenylethylenediamine) and [Co(acac)2(Me-en)]+ (Me-en=N-methylethylenediamine) in aqueous solutions have been measured at 34.0 °C. The Ph-en complex, which has an electron-withdrawing phenyl group on the nitrogen atom undergoes proton exchange about 104 times faster than the Me-en complex which has an electron-repelling methyl group. The proton-exchange rates are ca. 102 and 105 times greater than the inversion rates for the Ph-en and Me-en complexes, respectively. The faster rate of inversion for the Ph-en complex was explained by the lower barrier of inversion; an increased stabilization of the intermediate was due to (p-p)π conjugation between the amide nitrogen atom and the phenyl group.

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