Aryl Grignard cross-coupling of aryl chlorides catalysed by new, highly active phosphine/imidazolium nickel(II) complexes

Abstract

Two new zwitterionic Nickel(II) complexes, bearing phosphine/imidazolium ligands, have been prepared. Their catalytic activity, and the activity of an analogous Ni(II) complex, previously described by us, has been evaluated with a range of aryl chlorides, an aryl bromide and arylmagnesium halides. The catalytic activity is related to the length of the tether between the carbene and phosphine moieties. Thus the catalysts possessing a 6-membered metallacycle are more active than that having a 7-membered metallacycle. Changing from a mesityl (Mes) to a 2,6-diisopropylphenyl (DIP) on the imidazole ring does not strongly influence the activity. The three complexes show moderate to very good activities with most substrates, and enhanced selectivities compared to previously published Ni(II)/N-heterocyclic carbene systems. The low activity observed with 4-chlorobenzotrifluoride seems to be related to the presence of a phosphine on the ligands.

Di‐ and Trinuclear Gold Complexes of Diphenylphosphinoethyl‐Functionalised Imidazolium Salts and their N‐Heterocyclic Carbenes: Synthesis and Photophysical Properties

“…[47] The ligand motif was further used-with different anions or N-substituents (Mes, Ph, iPr, Et, Me, H)-as monodentate or pincer-type ligand for several complexes with palladium, nickel, iridium, and ruthenium, in which the carbene was either prepared first or generated by deprotonation in the presence of a metal precursor. [38,[48][49][50][51][52][53][54][55][56][57][58][59][60][61][62] In 2006, Hahn and Lee et al successfully used silver complexes of phosphine-functionalised benzimidazolin-2-ylidenes as transmetallating agents for the preparation of palladium and platinum compounds. [37,63,64] According to X-ray crystallographic data [64] it seems reasonable that the reaction of phosphine-fuctionalised imidazolium salts with silver oxide leads to different silver species, including those with silver ions coordinating to phosphines.…”

Nickel-Catalyzed Cross-Couplings Involving Carbon−Oxygen Bonds

“…Ni-NHCs were investigated as active catalysts for Kumada cross-coupling (Scheme 73). The active catalyst was either obtained in-situ270,271,272 or was synthesized beforehand and used subsequently in the cross-coupling 273,274,268,237,275,276. Aryl triflates and halides including fluorides were successfully coupled with aryl Grignard in medium to excellent yields.…”

Hydrosilylation reactions catalyzed by rhodium complexes with phosphine ligands functionalized with imidazolium salts

“…The second method, described by Tsoureas et al [17], involved a phosphine oxide intermediate that had to be reduced under harsh conditions. A synthetic method reported by Poli et al [18] was based on quaternization of N-mesitylimidazole with 1-bromoethanol to give 1-hydroxyethylene-3-mesitylimidazolium bromide (Scheme 4). Our synthetic method is based on the quaternization of N-alkylimidazoles with Br(CH 2 ) n Cl (n ¼ 2 or 3) to give 1-(n-chloroalkyl)-3-alkyl- Wave numbers(cm -1 ) 1584 Fig.…”