[2-(Alkylideneamino)benzoato]nickel(II) Complexes: Active Catalysts for Ethylene Polymerization

The complexes [RR‘CNC6H4C(O)O-κ2N,O]Ni(η3-CH2CMeCH2) (R, R‘ = −(CH2)5−, 6; R =
Et, R‘ = Et, 7; R = tBu, R‘ = H, 8) are prepared by reaction of the corresponding potassium
salts with [(η3-CH2CMeCH2)NiCl]2 in CH3CN. Additions of 1 equiv of B(C6F5)3 afford the
zwitterionic complexes [RR‘CNC6H4C{OB(C6F5)3}O-κ2N,O]Ni(η3-CH2CMeCH2) (R, R‘ =
−(CH2)5−, 9; R = Et, R‘ = Et, 10; R = tBu, R‘ = H, 11), which give poly(ethylene) when
ethylene gas is added. This result is interesting in that the corresponding 2-(diphenylphosphino)benzoato and 2-(diphenylamino)benzoato complexes give mainly butene. Reactions of
the potassium salts with Ni(η3-CH2C6H5)Cl(PMe3) afford benzyl complexes, [RR‘CNC6H4C(O)O-κ2N,O]Ni(η1-CH2C6H5)(PMe3) (R, R‘ = −(CH2)5−, 12; R = Et, R‘ = Et, 13). Additions of
2 equiv of B(C6F5)3 to 12 and 13 afford the zwitterionic η3-benzyl complexes [RR‘CNC6H4C{OB(C6F5)3}O-κ2N,O]Ni(η3-CH2C6H5) (R, R‘ = −(CH2)5−, 14; R = Et, R‘ = Et, 15). Complex
14 is rather unstable, and a bis ligand complex, [(CH2)5CNC6H4C{OB(C6F5)3}O-κ2N,O]2Ni
(16), is formed during recrystallization. Complexes 14 and 15 are highly active to ethylene
polymerization, and activities reach 3000−4000 kg/((mol of Ni) h) at 75 psig pressure. Solid
structures of 6, 9, 11, 15, and 16 were determined by X-ray crystallography.