Moisture-stable Nickel Research Articles

Predominant intermolecular decarbonylative thioetherification of carboxylic acids using nickel precatalysts

We report a general method for direct decarbonylative thioetherification of carboxylic acids using air- and moisture-stable nickel precatalysts. In this approach, ubiquitous carboxylic acids are directly used as aryl electrophiles and common thiols serve as sulfide donors.

Decarbonylative thioetherification by nickel catalysis using air- and moisture-stable nickel precatalysts.

A general, highly selective method for decarbonylative thioetherification of aryl thioesters by C-S cleavage is reported. These reactions are promoted by a commercially-available, user-friendly, inexpensive, air- and moisture-stable nickel precatalyst. The process occurs with broad functional group tolerance, including free anilines, cyanides, ketones, halides and aryl esters, to efficiently generate thioethers using ubiquitous carboxylic acids as ultimate cross-coupling precursors (cf. conventional aryl halides or pseudohalides). Selectivity studies and site-selective orthogonal cross-coupling/thioetherification are described. This thioester activation/coupling has been highlighted in the expedient synthesis of biorelevant drug analogue. In light of the synthetic utility of thioethers and Ni(ii) precatalysts, we anticipate that this user-friendly method will be of broad interest.

Synthesis and catalytic activity of nickel(II) complexes of CNC pincer-type N-heterocyclic carbene ligands

Air- and moisture-stable nickel(II) complexes 2a–c of CNC pincer-type N-heterocyclic carbene ligands have been prepared from the corresponding imidazolium salts by carbene–transfer reaction of a silver-NHC complex with Ni(DME)Cl2 (DME = dimethoxylethane). Pincer complexes 2a–c are characterized by mass and NMR spectroscopy. The structure of 2a is also identified by X-ray diffraction analysis. Pincer complex 2a has been shown to be active catalyst for the Suzuki coupling reactions.

Enhanced Activity of [Ni(NHC)CpCl] Complexes in Arylamination Catalysis

Seven new air- and moisture-stable nickel complexes bearing flexible bulky NHC (N-heterocyclic carbene) ancillary ligands (NHC = IPr*, IPr*Tol, IPr*OMe, IPent) are reported. Using experimentally determined crystal structures, the steric environments of [Ni(NHC)CpCl] complexes were analyzed. A survey of their catalytic activity in Buchwald–Hartwig arylamination has been performed. In comparison to less sterically demanding analogues (NHC = IMes, SIMes, IPr, SIPr), an increase in the ligand bulkiness was found to correlate to a dramatic enhancement of the C–N bond formation efficiency. Finally, the catalytic activity of the most active precatalyst, [Ni(IPr*OMe)CpCl], was further explored and the scope and limitations of this complex were examined.

Chiral Nickel(II) and Palladium(II) NCN-Pincer Complexes Based on Substituted Benzene: Synthesis, Structure, and Lewis Acidity

Air- and moisture-stable nickel(II) and palladium(II) complexes from phebox pincer ligands 1−5 have been synthesized, and their Lewis activity was investigated. 2,6-Bis(oxazolinyl)phenylnickel halide complexes [NiX(phebox)] and 2,6-bis(oxazolinyl)phenylpalladium halide complexes [PdX(phebox)] were synthesized via oxidative addition with [Ni(COD)2] or Pd2dba3, respectively, followed by halide abstraction using silver(I) salts to form complexes such as [Ni(phebox)][ClO4] (41). Herein, X-ray crystal structures are reported for several pincer complexes having the expected square-planar geometries with the terdentate NCN pincer system. Complexes with general structure [M(phebox)]X where X is a halogen showed no relative Lewis acidity. On the other hand, complexes where X was exchanged for a less coordinating counterion showed increased Lewis acidity. The relative Lewis acidity varies depending on the substituents on the benzene core of the pincer ligands, due to the electronic effects of the ligand on the metal center.

Synthesis and Catalytic Activity of a Pincer-Type Bis(imidazolin-2-ylidene) Nickel(II) Complex

An air- and moisture-stable nickel(II) complex of bis-carbene pincer complex 2 has been synthesized, and its catalytic activity for the Heck reaction and the Suzuki coupling reaction was investigated.