Inorg. Chem. 1987, 26, 2073-2078
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It appears that the extra ionic charge of 2C02imH- is an advantage in its role of x-donation for the parent imidazole series, but loses importance relative to a full anion charge localized on the fivemembered ring. Therefore its position in the T-donor series shifts below im- and above 2CH,imH; the other neutral R substituents remain in their logical electron-releasing order: CH(OH)2 3 CH, > H. Once the imidazolato form is created by deprotonation of the neutral parent ring structure, less assistance is provided by the 2-substituent in lowering the dx ( T ' ) transition ~ energy. The additional shifts on the x,-based transition are calculated to be 3364 cm-I, R = -CH(OH),; 4737 cm-', R = -CH,-; 5376 cm-I, R = -CH3; and 5347 cm-I, R = H. Therefore -CH3 is actually the better releasing group toward the anionic ring, compared to R = -CH(OH),.
545,376 >376 >376 >376 >376 370 367 363 338 300
