Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 21, Issue 20, Pages 7480-7488Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201500110
Keywords
alkyl halides; borylation; cross-coupling; density functional calculations; reaction mechanisms
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Funding
- Research Grants Council of Hong Kong [HKUST603313, CUHK7/CRF/12G]
- DFG [GZ: MA 4471/1-1, AOBJ: 609090]
- Hong Kong PhD Fellowship Scheme [PF11-08816]
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The nickel-catalyzed alkyl-alkyl cross-coupling (C-C bond formation) and borylation (C-B bond formation) of unactivated alkyl halides reported in the literature show completely opposite reactivity orders in the reactions of primary, secondary, and tertiary alkyl bromides. The proposed Ni-I/Ni-III catalytic cycles for these two types of bond-formation reactions were studied computationally by means of DFT calculations at the B3LYP level. These calculations indicate that the rate-determining step for alkyl-alkyl cross-coupling is the reductive elimination step, whereas for borylation the rate is determined mainly by the atom-transfer step. In borylation reactions, the boryl ligand involved has an empty p orbital, which strongly facilitates the reductive elimination step. The inability of unactivated tertiary alkyl halides to undergo alkyl-alkyl cross-coupling is mainly due to the moderately high reductive elimination barrier.
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