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

A novel potentially tridentate N-heterocyclic carbene (NHC) precursor, anionic salicylaldimine-functionalized imidazolium bromide, [3,5-tBu2-2-(HO)C6H2CHNCH2CH2(CH{NCHCHNiPr})Br] (HL·HBr, 2), was designed. The reaction of in situ-generated monoanionic
tridentate salicylaldiminato-functionalized NHC LNa with Ni(PPh3)2Br2 affords a novel mono-ligand Ni(II) bromide, [3,5-tBu2-2-(O)C6H2CHNCH2CH2(C{NCHCHNiPr})]NiBr (LNiBr, 3),
in good yield. Complex 3 can also be synthesized by the direct reaction of nickelocene (Cp)2Ni
or bis-indenyl Ni(II) complex (Ind)2Ni 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 NaBPh4 at 80 °C.