Physical Organic Chemistry of Transition Metal Carbene Complexes. 14.1 Thermodynamic Acidity Measurements of Fischer Carbene Complexes in Acetonitrile
详细信息 查看全文
- 作者：Claude F. Bernasconi ; Aquiles E. Leyes ; Mark L. Ragains ; Yan Shi ; Huan Wang ; and William D. Wulff
- 刊名：Journal of the American Chemical Society
- 出版年：1998
- 出版时间：September 2, 1998
- 年：1998
- 卷：120
- 期：34
- 页码：8632 - 8639
- 全文大小：177K
- 年卷期：v.120,no.34(September 2, 1998)
- ISSN：1520-5126
文摘
The pKa values of five Fischer carbene complexes of the general structure (CO)5Cr=C(OR)CHR'R'',of two (CO)4(PR3)Cr=C(OCH3)CH3 type complexes and of one aminocarbene complex, (CO)5Cr=C(NCH(CH3) CH2)CH3, were determined in acetonitrile by a spectrophotometric method. These pKa values span arange from 22.2 for (CO)5Cr=C(OCH3)CH3 to 27.6 for (CO)5Cr=C(NCH(CH3)C H2)CH3. Deprotonation ofthe carbene complexes was achieved with strong amine bases such as TMG, DBU, and BEMP. Attempts atmeasuring the pKa of some other carbene complexes failed either because of instability of the respective anions(e.g., (CO)5Cr=C(OCH3)CH(CH3)2) or because the pKa was too high for deprotonation to occur ((CO)5Cr=C(N(CH3)2)CH3). Similarities and differences in the structural dependence of these acidities in acetonitrilecompared to other solvents such as 50% acetonitrile-50% water, DMSO, and THF are discussed.