| 15252604 |
Lam WH, Lam KC, Lin Z, Shimada S, Perutz RN, Marder TB: Theoretical study of reaction pathways for the rhodium phosphine-catalysed borylation of C-H bonds with pinacolborane. Dalton Trans. 2004 May 21;(10):1556-62. Epub 2004 Apr 19.
The reaction mechanism of the rhodium-phosphine catalysed borylation of methyl-substituted arenes using pinacolborane (HBpin) has been investigated theoretically using DFT calculations at the B3PW91 level. Factors affecting selectivity for benzylic vs. aromatic C-H bond activation have been examined. It was found that [Rh (PR3) 2 (H)] is the active species which oxidatively adds the C-H bond leading to an eta3-benzyl complex which is the key to determining the unusual benzylic regioselectivity observed experimentally for this catalyst system. Subsequent reaction with HBpin leads to a [Rh (PR3) 2 (eta3-benzyl)(H)(Bpin)] complex from which B-C reductive elimination provides product and regenerates the catalyst. The electrophilic nature of the boryl ligand assists in the reductive elimination process. In contrast to Ir (L) 2 (boryl) 3-based catalysts, for which Ir (III)-Ir (V) cycles have been proposed, the Rh (I)-Rh (III) cycle is operating with the system addressed herein. |
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