Stabilization of Nickel(0) by Hemilabile P,N-Ferrocene Ligands and Their Ethylene Oligomerization Activities

Ligand displacement reactions of Ni(COD)2 with a ferrocenediyl iminophosphine, viz., [C5H4CHN(C6F5)]Fe[η-C5H4PPh2] (1) or [C5H4CHNC(H)(CH3)(C6H5)]Fe[η-C5H4PCy2] (2), in the presence of
t-BuNC, CO, or PhC⋮CPh give the appropriate mixed-ligand Ni(0) complexes, viz., [C5H4CHN(C6F5)]Fe[η-C5H4PPh2]Ni0(CNt-Bu)3 (3), [C5H4CHN(C6F5)]Fe[η-C5H4PPh2]Ni0(CO)2 (4a), {[C5H4CHN(C6F5)]Fe[η-C5H4PPh2]}2Ni0(CO)2 (4b), and [C5H4CHNC(H)(CH3)(C6H5)]Fe[η-C5H4PCy2]Ni0(η2-PhC⋮CPh) (5). The X-ray crystal and molecular structures of 4b and 5 are described. The hemilability
of iminophosphine is illustrated by the formation of both P,N-chelating and imine-pendant functions. All
the complexes examined are catalytically active toward ethylene oligomerization at 30 °C, with 5 showing
the best activity, followed by 3 and 4.