A Modular, Air-Stable Nickel Precatalyst

Abstract

The synthesis and catalytic activity of [(TMEDA)Ni(otolyl) Cl], an air-stable, crystalline solid, is described. This complex is an effective precatalyst in a variety of nickel-catalyzed transformations. The lability of TMEDA allows a wide variety of ligands to be used, including mono- and bidentate phosphines, diimines, and N-heterocyclic carbenes. Preliminary mechanistic studies are also reported, which suggest that [(TMEDA)Ni(o-tolyl)Cl] can activate by either a Ni–B or Ni–Ni transmetalation event, depending on the reaction conditions.

Well-defined nickel and palladium precatalysts for cross-coupling

“…141), whereas most Ni precatalysts have only been used with more traditional monophosphines such as PPh 3 or PCy 3 . Activation of precatalysts of the type [L n Ni(Ar)X] generally involves transmetallation of the halo ligand with the nucleophile in cross-coupling followed by reductive elimination 140,142,143 . So far, there has been limited examination of the rates of the activation process under different reaction conditions, and detailed studies exploring this topic would assist in the optimization of reactions 140 .…”

“…The nitrogen chelate complex [(TMEDA)Ni( o -tolyl)Cl] (TMEDA = N , N , N′ , N′ -tetramethylethylenediamine), which was simultaneously reported by the groups of Doyle 143 and Monfette 153 , is of particular significance to rapid ligand screening. When mixed with ligands such as phosphines or NHCs, it generates active precatalysts for the Suzuki–Miyaura, Heck and Buchwald–Hartwig coupling reactions, as well as for cyclization and α-arylation reactions.…”

“…This system is one of the first bench-stable Ni-based precatalysts suitable for ligand screening and compatible with a large range of ligands. However, one drawback is the potential for the free TMEDA to poison some catalytic reactions 143 .…”

A Unified and Practical Method for Carbon–Heteroatom Cross‐Coupling using Nickel/Photo Dual Catalysis

“…Surprisingly, for aryl chloride 2 b under the optimized conditions, no reactivity was observed when K 2 CO 3 was used; however, when Na 2 CO 3 was used instead a modest yield of 61 % was realized. Moreover, when Ni(COD) 2 was used as the nickel source a yield of 90 % was observed, while use of Doyle's precatalyst gave reduced yields. Finally, a photocatalyst screen was performed, including those with high oxidation potentials in the excited state, compared to Ir(ppy) 3 ( E 1/2 red Ir III */Ir II =+0.31 V), such as [Ir(dF(CF 3 )ppy) 3 (dtbpy)]PF 6 ( E 1/2 red Ir III */Ir II =+1.21 V) 3e and [Ru(bpy) 3 ]Cl 2 ( E 1/2 red Ru II */Ru I =+0.77 V), and it was observed that such catalysts yielded no product.…”

A Transmetalation Reaction Enables the Synthesis of [18F]5-Fluorouracil from [18F]Fluoride for Human PET Imaging

“…Nickel σ-aryl complexes are employed as precatalysts, 8 substrates for mechanistic investigation, 9 and precursors for late-stage 18 F-fluorination. 10 Nickel σ-aryl complexes react with [ 18 F]fluoride and oxidant in less than 1 min at 23 °C in the presence of water to afford [ 18 F]aryl fluorides.…”