Synthesis of Salicylaldiminato-Functionalized N-Heterocyclic Carbene Complex of Nickel(II) and Its Catalytic Activity for Styrene Polymerization

Abstract

A novel potentially tridentate N-heterocyclic carbene (NHC) precursor, anionic salicylaldimine-functionalized imidazolium bromide, [3,5-t Bu 2 -2-(HO)C 6 H 2 CHdNCH 2 CH 2 (CH-{NCHCHN i Pr})Br] (HL‚HBr, 2), was designed. The reaction of in situ-generated monoanionic tridentate salicylaldiminato-functionalized NHC LNa with Ni(PPh 3 ) 2 Br 2 affords a novel monoligand Ni(II) bromide, [3,5-t Bu 2 -2-(O)C 6 H 2 CHdNCH 2 CH 2 (C{NCHCHN i Pr})]NiBr (LNiBr , 3), in good yield. Complex 3 can also be synthesized by the direct reaction of nickelocene (Cp) 2 Ni or bis-indenyl Ni(II) complex (Ind) 2 Ni with 2 in high yield via the cyclopentadiene or indene elimination reaction, respectively. Complex 3 has been fully characterized including X-ray structural determination. Preliminary study indicated that 3 shows good catalytic activity for the polymerization of styrene in the presence of NaBPh 4 at 80 °C.

Formation of Homoleptic Tetracarbene versus cis‐Chelating Dicarbene Complexes of Nickel(II) and Applications in Kumada–Corriu Couplings

“…In particular, Pd-NHC complexes have been widely used in the making of C-C bonds often by employing the Mizoroki-Heck and Suzuki-Miyaura coupling reactions. Similarly, some Ni-NHC complexes have shown to be catalytically active for a wide range of reactions such as SuzukiMiyaura [21,22] and Kumada-Corriu [23][24][25][26][27][28] couplings, olefin dimerization [3] and polymerization, [29][30][31][32] C-C bond activation of biphenylene, [33] transfer hydrogenation of imines, [34] and amination [35] and dehalogenation [36] of aryl halides. Notably, most of these nickel complexes contain NHC ligands that are derived either from imidazole or imidazoline precursors, whereas the catalytic activity of Ni IIbenzimidazolin-2-ylidenes have rarely been studied.…”

Donor‐Functionalised N‐Heterocyclic Carbene Complexes of Group 9 and 10 Metals in Catalysis: Trends and Directions

“…[86,[113][114][115][116] These key studies demonstrate that chelating ligand systems can provide a degree of stability against the facile reductive elimination process previously noted for monodentate NHC complexes of Ni. [24] However, it appears that the reductive elimination from these hemilabile systems may still lead to catalyst deactivation.…”

“…In the same way that phosphane-based ligands have undergone important design stages, novel df-NHC ligands are now being designed and their performance investigated; in further polymerisation studies, the Ni II complex 73 (Figure 17) was treated with NaBPh 4 and tested as a catalyst for the polymerisation of styrene, at 80°C in toluene. [114] On the basis of the relatively high average molecular weight of the resultant polymer it was suggested that the catalysts with a tridentate salicylaldiminato-carbene demonstrate higher stability. The same group also studied the polymerisation of styrene using a Ni II complex containing an NHC functionalised with a C3-bridged indenyl group, 74.…”

Aluminium Complexes of a Phenoxyimine Ligand with a Pendant Imidazolium Moiety: Synthesis, Characterisation and Evidence for Hydrogen Bonding in Solution

“…[6,7] Well re-solved 1 H NMR spectra of these ligands are reported in the Supporting Information; the assignments of the protonic resonances were based on previously reported data, and in the case of phimid-H·Br were corroborated by long-range 1 H-1 H COSY experiments. Recrystallisation of phimidH·Br from hexane/diethyl ether afforded crystals suitable for X-ray analysis.…”

“…In particular we considered the salicylaldimine-functionalised imidazolium bromide ligand [3,5-tBu 2 -2-(OH)C 6 H 2 CH=NCH 2 CH 2 (CH{NCH-CHNiPr})]Br (phimid-H·Br), previously employed in the synthesis of N-heterocyclic carbene complexes of late transition and lanthanide metals. [6] Here we describe the synthesis, solution properties and reactivity of novel alkylaluminium complexes bearing the phimid-H·Br ligand. The distinctive behaviour of these complexes is compared with that of an analogous alkylaluminium complex bearing a salicylaldimine ligand lacking the pendant imidazolium moiety: 3,5-tBu 2 -2-(OH)C 6 H 2 CH= NiPr (phim-H).…”