Facile Suzuki-Miyaura coupling of activated aryl halides using new CpNiBr(NHC) complexes

Abstract

Highlights • Synthesis of nine new Ni(II)-NHC complexes, [CpNiBr(NHC)].• Symmetric and asymmetric alkyl/-benzyl/phenylethyl substituted NHC complexes of Ni.• Suzuki-Miyaura coupling of activated aryl halides with phenylboronic acid. Graphical abstract AbstractNine new Ni(II)-NHC complexes, [CpNiBr(NHC)], were synthesised from nickelocene and the corresponding symmetric or asymmetric alkyl/-benzyl/phenylethyl imidazolium bromide ligands in relatively high yield. Access to each of the synthesised symmetric or asymmetric alkyl/benzyl/phenylethyl imidazolium bromide salts was obtained through deprotonation of imidazole, followed by treatment with an alkyl-or aryl halide, which is subsequently followed with reaction of a secondary alkyl-, benzyl-, or phenylethyl halide. The series of [CpNiBr(NHC)] exhibited catalytic activity in the Suzuki-Miyaura coupling of activated aryl halides with phenylboronic acid to give the respective biphenyl and biphenyl-containing products. In general, the more electron-donating NHC-bearing Ni complexes showed higher

Nickel(II) Phosphane‐ and N‐heterocyclic Carbene Complexes with Tridentate, Dianionic [S,N,O]2– Ligands

“…Thus, more electron‐withdrawing NHCs result in a higher chemical shift of the carbenic carbon atom. A similar trend has been observed by Landman in a series of cyclopentadienyl nickel(II) carbenes of the type [CpNiBr(NHC)] . The molecular structures of three representative complexes ( 3 , 4 and 6 ) were determined by single‐crystal X‐ray diffraction (Figure , Figure , and Figure ).…”

Electrochemistry of a series of symmetric and asymmetric CpNiBr(NHC) complexes: Probing the electrochemical environment due to push-pull effects

“…The neutral series of [CpNi(II)Br(NHC)] two-legged piano stool complexes were modelled as low spin diamagnetic (singlet multiplicity) d 8 complexes since the singlet calculations resulted in lower energies (0.09-0.12 eV) compared to triplet multiplicity calculations, for all complexes. complexes 1-9 containing flexible symmetric-and asymmetric NHC ligands, has been described in the literature [30,31]. The general synthesis involves the reflux of an anhydrous THF slurry containing imidazolium bromide [HIm]Br and one equivalent of nickelocene (NiCp2) for 3-16 hours (depending on the NHC salt), see Figure 2.…”

“…The general synthesis involves the reflux of an anhydrous THF slurry containing imidazolium bromide [HIm]Br and one equivalent of nickelocene (NiCp2) for 3-16 hours (depending on the NHC salt), see Figure 2. The reaction mixture is then concentrated in vacuo, subjected to column chromatography (DCM/hexane), after which the collected red fraction was concentrated in vacuo to obtain red to red-brown powders [30].…”

“…Column chromatography was carried out under inert argon atmospheres using silica gel (particle size 0.063-0.200 mm) as the stationary phase. The synthesis, purification, and characterisation of complexes [CpNiBr(NHC)] (1-9) ( Figure 1) were performed as previously reported by our group [30]. All other chemicals were purchased from Sigma-Aldrich and used without further purification.…”

“…We have recently extended the existing limited range [21, 27 -29 ] of [CpNiBr (NHC)] complexes to include bulky, flexible symmetric and asymmetric NHC ligands, which were found to be catalytically active for Suzuki-Miyaura coupling [30] and anaerobic secondary alcohol oxidation reactions [ 31 ]. Despite their versatile application possibilities, electrochemical studies on the redox properties of this class of [CpNiX(NHC)] (X = Cl, Br, I)…”