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Exploring Regioselective Bond Cleavage and Cross-Coupling Reactions using a Low-Valent Nickel Complex

TitleExploring Regioselective Bond Cleavage and Cross-Coupling Reactions using a Low-Valent Nickel Complex
Publication TypeJournal Article
Year of Publication2016
AuthorsDesnoyer, AN, Friese, FW, Chiu, W, Drover, MW, Patrick, BO, Love, JA
JournalChemistry – A European Journal
Volume22
Pagination4070–4077
ISSN1521-3765
KeywordsCROSS-COUPLING, ELIMINATION, NICKEL, P ligands, SULFUR
Abstract

Recently, esters have received much attention as transmetalation partners for cross-coupling reactions. Herein, we report a systematic study of the reactivity of a series of esters and thioesters with [{(dtbpe)Ni}2(μ-η2:η2-C6H6)] (dtbpe=1,2-bis(di-tert-butyl)phosphinoethane), which is a source of (dtbpe)nickel(0). Trifluoromethylthioesters were found to form η2-carbonyl complexes. In contrast, acetylthioesters underwent rapid Cacyl−S bond cleavage followed by decarbonylation to generate methylnickel complexes. This decarbonylation could be pushed backwards by the addition of CO, allowing for regeneration of the thioester. Most of the thioester complexes were found to undergo stoichiometric cross-coupling with phenylboronic acid to yield sulfides. While ethyl trifluoroacetate was also found to form an η2-carbonyl complex, phenyl esters were found to predominantly undergo Caryl−O bond cleavage to yield arylnickel complexes. These could also undergo transmetalation to yield biaryls. Attempts to render the reactions catalytic were hindered by ligand scrambling to yield nickel bis(acetate) complexes, the formation of which was supported by independent syntheses. Finally, 2-naphthyl acetate was also found to undergo clean Caryl−O bond cleavage, and although stoichiometric cross-coupling with phenylboronic acid proceeded with good yield, catalytic turnover has so far proven elusive.

URLhttp://dx.doi.org/10.1002/chem.201504959
DOI10.1002/chem.201504959