10474-32-5Relevant articles and documents
Diboron-Promoted Reduction of Ni(II) Salts: Precatalyst Activation Studies Relevant to Ni-Catalyzed Borylation Reactions
Joannou, Matthew V.,Sarjeant, Amy A.,Wisniewski, Steven R.
, p. 2691 - 2700 (2021/08/20)
The activation and reduction of nickel(II) salts under conditions relevant to Ni-catalyzed borylation reactions is reported. Methanolic solutions of NiCl2·6H2O reacted with >2 equiv of (iPr)2NEt were converted to polymeric Ni(OMe)2, which was characterized by IR spectroscopy, magnetic susceptibility measurements, and verified by independent synthesis from NaOMe. When diboron reagents such as bis(neopentylglycolato) diboron (B2(npg)2) were exposed to methanolic solutions of Ni(II) salts and (iPr)2NEt, nickel metal was deposited along with the evolution of hydrogen gas. A direct relationship between yield of nickel metal and equivalents of B2(npg)2 relative to [Ni] was also observed, reaching >99% yield at 8 equiv. Ni(0) coordination complexes were also isolated when a phosphine, phosphite, and/or diene ligand was present, all starting from NiCl2·6H2O, including the following: Ni[P(OPh)3]4 (74% yield), Ni[P(OiPr)3]4 (54% yield), Ni(PPh3)4 (75% yield), (dppp)2Ni + Ni(1,5-cod)2 (dppp = 1,3-bis(diphenylphosphine)propane) (91% yield), Ni(1,5-cod)2 (1,5-cod = 1,5-cyclooctadiene) (69% yield), and (dppf)Ni(1,5-cod) (dppf = 1,1′-bis(diphenylphosphino)ferrocene) (84% yield). The high yields observed indicated the efficient reduction of Ni(II) to Ni(0) and a likely route for precatalyst entry into the Ni-borylation catalytic cycle. These in situ reduction conditions were also successfully applied to a previously developed Ni-catalyzed alpha-arylation reaction where the requisite Ni(1,5-cod)2 precatalyst was substituted for NiCl2·6H2O and catalytic diboron. Comparable yields to the original report were observed under these conditions, further demonstrating that Ni(0) active species can be efficiently accessed with diboron reagents under protic conditions from Ni(II) salt hydrates.
Nickel-catalyzed enantioselective C-C bond formation through C sp 2 -O cleavage in aryl esters
Cornella, Josep,Jackson, Evan P.,Martin, Ruben
supporting information, p. 4075 - 4078 (2015/03/30)
We report the first enantioselective C-C bond formation through C-O bond cleavage using aryl ester counterparts. This method is characterized by its wide substrate scope and results in the formation of quaternary stereogenic centers with high yields and asymmetric induction.
Nickel-catalyzed asymmetric α-arylation and heteroarylation of ketones with chloroarenes: Effect of halide on selectivity, oxidation state, and room-temperature reactions
Ge, Shaozhong,Hartwig, John F.
supporting information; experimental part, p. 16330 - 16333 (2011/11/29)
We report the α-arylation of ketones with a range of aryl chlorides with enantioselectivities from 90 to 99% ee catalyzed by the combination of Ni(COD)2 and (R)-BINAP and the coupling of ketones with a range of heteroaryl chlorides with enantioselectivities up to 99% ee catalyzed by Ni(COD)2 and (R)-DIFLUORPHOS. The analogous reactions of bromoarenes occur with much lower enantioselectivities. Mechanistic studies showed that the difference in the rates of decomposition of the arylnickel(II) halide intermediates to {[(R)-BINAP]NiX}2 likely accounts for the difference in the enantioselectivities of the reactions of bromoarenes and chloroarenes. This catalyst decomposition can be overcome by conducting the reactions with [(R)-BINAP]Ni(η2-NC-Ph) (4), which undergoes oxidative addition to haloarenes at room temperature.