Synthesis and characterization of N-(2-pyridyl)benzamide-based nickel complexes and their activity for ethylene oligomerization

Abstract A series of N -(2-pyridyl)benzamides ( 1 )–( 11 ) and their nickel complexes, [ N -(2-pyridyl)benzamide]dinickel(II) di-μ-bromide dibromide ( 12 )–( 16 ) and (aryl)[ N -(2-pyridyl)benzamido](triphenylphosphine)nickel(II) ( 17 )–( 24 ), were synthesized and characterized. The single-crystal X-ray analysis revealed that 12 and 14 are binuclear nickel complexes bridged by bromine atoms and each nickel atom adopts a distorted trigonal bipyramidal geometry. The key feature of the complexes 17 , 19 and 23 is each has a six-membered nickel chelate ring including a deprotonated secondary nitrogen atom and an O-donor atom. The nickel complexes show moderate to high catalytic activity for ethylene oligomerization with methylaluminoxane (MAO) as cocatalyst. The activity of 12 – 16 /MAO systems is up to 3.3 × 10 4 g mol −1 h −1 whereas for 17 – 24 /MAO systems it is up to 4.94 × 10 5 g mol −1 atm −1 h −1 . The influence of Al/Ni molar ratio, reaction temperature, reaction period and PPh 3 /Ni molar ratio on catalytic activity was investigated.