Synthesis, Characterization, and Reactivity Studies of (Cyclohexenyl)nickel(II) Complexes

The synthesis and characterization of the complexes [(cyclohexenyl)Ni(NCMe)2][B(ArF)4] (1) and [(cyclohexenyl)Ni(mesitylene)][B(ArF)4] (2) are reported. Abstraction
of the nitrile ligands in 1 with B(C6F5)3 yields a “ligand-free” [(cyclohexenyl)NiII]+ species which coordinates 1,3-dienes, including
butadiene (BD), isoprene (IP), 1,3-cyclohexadiene (1,3-CHD), 1,4-cyclohexadiene
(1,4-CHD), and 2,3-dimethyl-1,3-butadiene (DMBD) at low temperatures.
Diene insertion is observed at temperatures above ca. −20 °C.
An s-trans diene complex is formed upon coordination
of DMBD. Hydrogen transfer is observed when complex 2 is exposed to 1-hexene or cyclopentadiene to generate new allyl
nickel complexes and 1 equiv of cyclohexene. Polymerization of 1,3-CHD
and DMBD with 2 is described, and a coupling product
formed between DMBD and 2 is observed and characterized.