| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 1300104 | Coordination Chemistry Reviews | 2013 | 12 Pages |
A comprehensive understanding of the CH bond cleavage step in direct arylation is important in further development of cross-coupling reactions using transition metal catalysts. Analysis of Pd-catalyzed CH bond cleavage of a wide range of (hetero)arenes via the concerted metalation–deprotonation (CMD) pathway allows one to quantify various contributions to the activation barriers and to identify activation characteristics of different substituent groups. In general, the CMD activation barriers do not show correlation with CH bond acidities and metalaryl bond energies. Regioselectivity of arylation for many (hetero)arenes, especially electron-deficient arenes, can be predicted from the CH bond acidities. Regioselectivity of arylation for different (hetero)arenes can be understood from the distortion and electronic interaction contributions to the CMD activation barriers. The effects of remote substituents and metal coordination to heteroarenes on reactivity and regioselectivity are discussed. Electron-withdrawing substituents and metal coordination to heteroatoms increase acidities of (hetero)arene CH bonds, making those bond more reactive in the CMD process.
Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (167 K)Download as PowerPoint slideHighlights► Analysis of Pd-catalyzed CH bond cleavage in (hetero)arenes. ► The CMD activation barriers do not show correlation with heterolytic metalaryl bond energies. ► Regioselectivity of arylation for (hetero)arenes can be understood from distortion and electronic interaction contributions. ► Regioselectivity of electron-deficient arenes can be predicted from CH bond acidities. ► Electron-withdrawing substituents and metal coordination to heteroatoms increase acidities of (hetero)arene CH bonds.
