title: Exploring Regioselective Bond Cleavage and Cross-Coupling Reactions using a Low-Valent Nickel Complex.
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-η(2):η(2)-C6H6)] (dtbpe=1,2-bis(di-tert-butyl)phosphinoethane), which is a source of (dtbpe)nickel(0). Trifluoromethylthioesters were found to form η(2)-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 η(2)-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.
authors.affiliation: Department of Chemistry, The University of British Columbia, 2036 Main Mall, Vancouver, V6T 1Z1, Canada.
authors.forename: Addison N
authors.initials: AN
authors.lastname: Desnoyer
authors.affiliation: Organisch-Chemisches Institut, Westfälische Wilhelms-Universität Münster, Corrensstraβe 40, 48149, Münster, Germany.
authors.forename: Florian W
authors.initials: FW
authors.lastname: Friese
authors.affiliation: Department of Chemistry, The University of British Columbia, 2036 Main Mall, Vancouver, V6T 1Z1, Canada.
authors.forename: Weiling
authors.initials: W
authors.lastname: Chiu
authors.affiliation: Department of Chemistry, The University of British Columbia, 2036 Main Mall, Vancouver, V6T 1Z1, Canada.
authors.forename: Marcus W
authors.initials: MW
authors.lastname: Drover
authors.affiliation: Department of Chemistry, The University of British Columbia, 2036 Main Mall, Vancouver, V6T 1Z1, Canada.
authors.forename: Brian O
authors.initials: BO
authors.lastname: Patrick
authors.affiliation: Department of Chemistry, The University of British Columbia, 2036 Main Mall, Vancouver, V6T 1Z1, Canada. jenlove@chem.ubc.ca.
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Love
keywords: P ligands; cross-coupling; elimination; nickel; sulfur