title: Mechanistic Study of an Improved Ni Precatalyst for Suzuki-Miyaura Reactions of Aryl Sulfamates: Understanding the Role of Ni(I) Species.
abstract: Nickel precatalysts are potentially a more sustainable alternative to traditional palladium precatalysts for the Suzuki-Miyaura coupling reaction. Currently, there is significant interest in Suzuki-Miyaura coupling reactions involving readily accessible phenolic derivatives such as aryl sulfamates, as the sulfamate moiety can act as a directing group for the prefunctionalization of the aromatic backbone of the electrophile prior to cross-coupling. By evaluating complexes in the Ni(0), (I), and (II) oxidation states we report a precatalyst, (dppf)Ni(o-tolyl)(Cl) (dppf = 1,1'-bis(diphenylphosphino)ferrocene), for Suzuki-Miyaura coupling reactions involving aryl sulfamates and boronic acids, which operates at a significantly lower catalyst loading and at milder reaction conditions than other reported systems. In some cases it can even function at room temperature. Mechanistic studies on precatalyst activation and the speciation of nickel during catalysis reveal that Ni(I) species are formed in the catalytic reaction via two different pathways: (i) the precatalyst (dppf)Ni(o-tolyl)(Cl) undergoes comproportionation with the active Ni(0) species; and (ii) the catalytic intermediate (dppf)Ni(Ar)(sulfamate) (Ar = aryl) undergoes comproportionation with the active Ni(0) species. In both cases the formation of Ni(I) is detrimental to catalysis, which is proposed to proceed via a Ni(0)/Ni(II) cycle. DFT calculations are used to support experimental observations and provide insight about the elementary steps involved in reactions directly on the catalytic cycle, as well as off-cycle processes. Our mechanistic investigation provides guidelines for designing even more active nickel catalysts.
authors.affiliation: The Department of Chemistry, Yale University , P.O. Box 208107, New Haven, Connecticut 06520, United States.
authors.forename: Megan
authors.initials: M
authors.lastname: Mohadjer Beromi
authors.affiliation: Centre for Theoretical and Computational Chemistry (CTCC), Department of Chemistry, University of Oslo , P.O. Box 1033, Blindern, 0315, Oslo, Norway.
authors.forename: Ainara
authors.initials: A
authors.lastname: Nova
authors.affiliation: Centre for Theoretical and Computational Chemistry (CTCC), Department of Chemistry, University of Oslo , P.O. Box 1033, Blindern, 0315, Oslo, Norway.
authors.forename: David
authors.initials: D
authors.lastname: Balcells
authors.affiliation: The Department of Chemistry, Yale University , P.O. Box 208107, New Haven, Connecticut 06520, United States.
authors.forename: Ann M
authors.initials: AM
authors.lastname: Brasacchio
authors.affiliation: The Department of Chemistry, Yale University , P.O. Box 208107, New Haven, Connecticut 06520, United States.
authors.forename: Gary W
authors.identifier: 0000-0002-7040-1892
authors.initials: GW
authors.lastname: Brudvig
authors.affiliation: The Department of Chemistry, Yale University , P.O. Box 208107, New Haven, Connecticut 06520, United States.
authors.forename: Louise M
authors.initials: LM
authors.lastname: Guard
authors.affiliation: The Department of Chemistry, Yale University , P.O. Box 208107, New Haven, Connecticut 06520, United States.
authors.forename: Nilay
authors.identifier: 0000-0001-8337-198X
authors.initials: N
authors.lastname: Hazari
authors.affiliation: The Department of Chemistry, Yale University , P.O. Box 208107, New Haven, Connecticut 06520, United States.
authors.forename: David J
authors.initials: DJ
authors.lastname: Vinyard
mesh_terms: D002384:Catalysis; D015394:Molecular Structure; D009532:Nickel / Q000737:chemistry*; D013451:Sulfonic Acids / Q000737:chemistry*
chemical_list: D013451:Sulfonic Acids; D009532:Nickel; C005741:sulfamic acid