Stoichiometric and Catalytic Aryl−Cl Activation and Borylation using NHC‐stabilized Nickel(0) Complexes

Abstract

NHC-nickel( NHC = N-heterocyclic carbene) complexes are efficient catalysts for the CÀCl bond borylation of aryl chlorides using NaOAc as ab ase and B 2 pin 2 (pin = pinacolato) as the boron source.T he catalysts [Ni 2 (ICy) 4 (m-(h 2 :h 2 )-COD)] (1,I Cy = 1,3-dicyclohexylimidazolin-2-ylidene;C OD = 1,5-cyclooctadiene), [Ni(ICy) 2 (h 2 -C 2 H 4 )] (2), and [Ni(ICy) 2 (h 2 -COE)] (3,C OE = cyclooctene) comparew ell with other nickel catalysts reported previously for aryl-chloride borylation with the advantage that no further ligandsh ad to be added to the reaction. Borylation also proceeded with B 2 neop 2 (neop = neopentylglycolato)a st he boron source. Stoichiometrico xidative addition of different aryl chlorides to complex 1 was highly selectivea ffording trans-[Ni(ICy) 2 (Cl)(Ar)]

NHC‐Stabilized Nickel Olefin, Dialkyl, and Dicyanido Complexes

“…The Ni–C distances to the NHC ligand of 1.898(2) Å and 1.892(2) Å ( 5 ), 1.886(4) Å and 1.887(4) Å ( 7 ), and 1.897(2) Å and 1.901(2) ( 8 ) are in line with those observed for the related complexes [Ni( i Pr 2 Im) 2 (η 2 ‐C 2 H 4 )] (1.905(2) Å, 1.915(2) Å) and [{Ni( i Pr 2 Im) 2 } 2 ( µ ‐(η 2 :η 2 )‐COD)] (1.906(3) Å, 1.904(3) Å). [4a] The Ni–C distances to the olefin ligands of 1.950(2) Å and 1.948(2) Å ( 5 ), 1.957(4) and 1.951(3) Å ( 7 ), and 1.967(2) Å and Ni–C16 1.953(2) Å ( 8 ) are similar to bond lengths observed earlier for NHC‐stabilized nickel olefin complexes ([Ni(Cy 2 Im) 2 (η 2 ‐COE)]: 1.984(6) Å, 1.953(6) Å; [{Ni( i Pr 2 Im) 2 } 2 ( µ ‐(η 2 :η 2 )‐COD)]: 1.995(3) Å, 1.989(3) Å,[4a] and [Ni(PPh 3 ) 2 (η 2 ‐ C 2 H 4 )]: 1.959(6) Å, 1.978(5) Å[4a]). The excellent charge transfer from the nickel atom to the ethylene and cyclooctene ligand and thus an indication for the high metal basicity of nickel is demonstrated by the enlargement of the C=C bonds to ca.…”

“…We reported earlier the synthesis of olefin complexes of the type [Ni(NHC) 2 (η 2 ‐olefin)] from the metallic reduction of trans ‐[Ni(NHC) 2 Br 2 ]. [4e], These complexes are suitable entries for NHC nickel(0) chemistry. With the dihalide complexes of the small NHCs Me 2 Im and Me 2 Im Me in hand we wanted to examine whether these protocols are also suitable for the synthesis of olefin complexes for the smallest of the NHC ligand family.…”

Ni‐Catalyzed Borylation of Aryl Sulfoxides

“…Subsequently, by applying a readily prepared NHC-stabilized nickel(0) catalyst precursor [Ni 2 (ICy) 4 {μ-(η 2 :η 2 )-COD}] (ICy = 1,3-dicyclohexylimidazolin-2-ylidene) and the base NaOAc, we demonstrated the catalytic CÀ Cl borylation of aryl chlorides. [23] Very recently, we reported an efficient [Ni(IMes) 2 ]catalyzed directed C3-selective CÀ H borylation of indoles. [24] In 2006, Hosoya [25a] and Yorimitsu [25b] independently demonstrated the borylation of aryl sulfides employing rhodium and palladium-NHC catalysts, respectively.…”

“…halides, [22,23] we envisioned transforming aryl sulfoxides to arylboronate esters using an NHC nickel catalyst. Inexpensive Ni and ligand were used in place of expensive Rh and Pd metals which were employed previously.…”

Copper‐Catalyzed Oxidative Cross‐Coupling of Electron‐Deficient Polyfluorophenylboronate Esters with Terminal Alkynes

“…Very recently, we reported optimized conditions for the Suzuki–Miyaura cross‐coupling of Ar F Bpin with aryl iodides and bromides using a combination of CuI and phenanthroline as a catalyst precursor to generate cross‐coupled products in moderate to excellent yields [20c] . We have recently reported the palladium‐catalyzed homocoupling of fluorinated arylboronates, [20d] and the borylation of aryl chlorides, using NHC‐stabilized nickel(0) complexes [20e] or a readily prepared NHC‐stabilized Cu catalyst [20f] . Inspired by these results, we attempted to develop a Cu‐catalyst system for the oxidative cross‐coupling of Ar F Bpin compounds with terminal alkynes.…”