The Anionic Pathway in the Nickel‐Catalysed Cross‐Coupling of Aryl Ethers

Abstract

The Ni-catalysed cross-coupling of aryl ethers is ap owerfulm ethod to forge new C À Ca nd C À heteroatom bonds.However,the inert C(sp 2 )ÀObond means that acanonical mechanism that relies on the oxidative addition of the aryl ether to aN i 0 centre is thermodynamically and kinetically unfavourable,which suggests that alternative mechanisms may be involved. Here,w ep rovides pectroscopic and structural insights into the anionic pathway,whichrelies on the formation of electron-rich hetero-bimetallic nickelates by adding organometallic nucleophiles to aN i 0 centre.A ssessing the rich cocomplexation chemistry between Ni(COD) 2 and PhLi has led to the structures and solution-state chemistry of ad iverse family of catalytically competent lithium nickelates being unveiled. In addition, we demonstrate dramatic solvent and donor effects,w hich suggest that the cooperative activation of the aryl ether substrate by Ni 0 -ate complexes playsakey role in the catalytic cycle.

A Non Expected Alternative Ni(0) Species in the Ni‐Catalytic Aldehyde and Alcohol Arylation Reactions Facilitated by a 1,5‐Diaza‐3,7‐diphosphacyclooctane Ligand

“…However, as stated above, this is not affordable thermodynamically. From intermediate II a second reaction can take place when R 1 I is inserted on this intermediate leading to the formation of III.1 which is also a Ni(0) species, in agreement with past work of Borys and Hevia, [52] Newman and coworkers, [39,53] and previously with palladium by Amatore and Jutand [54] . Then, the metal center is oxidized back to Ni(II) with the formation of III.2 .…”

Towards Hexagonal Planar Nickel: A Dispersion‐Stabilised Tri‐Lithium Nickelate

“…The Ni−C [Ni1−C1 1.8683(18) Å; Ni1−C9 1.856(2) Å] and C≡C bond lengths [C1−C2 1.232(3) Å; C9−C10 1.233(4) Å] are comparable to reported low‐valent nickel acetylides, [24] whilst the Li−C contacts [2.228(4)–2.267(4) Å] are typical for metalates containing TMEDA‐solvated lithium acetylides [25, 26] . The Ni−Li distances range from 2.487(4) Å to 2.512(3) Å which is within the sum of the covalent radii (2.52 Å) [27] and comparable to other lithium organonickelates derived from PhLi that we have reported containing TMEDA [22] . A Hirshfeld surface analysis [28] of 2 a (Figure 2a), in which red regions depict where contact distances between closest atoms below and above the surface are smaller than the sum of their van der Waals radii, further illustrates the existence of close contacts between Ni−Li and Li−C.…”

Towards Hexagonal Planar Nickel: A Dispersion‐Stabilised Tri‐Lithium Nickelate

“…This could be extended to other lithium aryl‐acetylides to give 2 b (Ar= p ‐Tol) and 2 c (Ar=3‐thienyl) in 85 % and 28 % yield, respectively (see Supporting Information for details and solid‐state structures). Akin to other alkali‐metal nickelates that we have reported, the choice of solvent and donor is key to enabling their synthesis and isolation [16, 21, 22] . Et 2 O and THF solvates of 2 a could not be isolated or spectroscopically observed, and the addition of 12‐crown‐4 to 2 a leads to immediate decomposition, illustrating that TMEDA plays an important role beyond lithium cation solvation (see below).…”