Methylene bridged binuclear bis(imino)pyridyl iron(II) complexes and their use as catalysts together with Al(i-Bu)3 for ethylene polymerization

Three novel methylene bridged binuclear iron(II) complexes: { [ 2 , 6 -R 2 -C 6 H 3 NC ( CH 3 ) C 5 H 3 N ( CH 3 ) CN ( 3 , 5 -R 2 ′ ) C 6 H 2 -CH 2 - ( 3 , 5 -R 2 ′ ) C 6 H 2 NC ( CH 3 ) C 5 H 3 N ( CH 3 ) CN ( 2 , 6 -R 2 ) C 6 H 3 ] [ FeCl 2 ] 2 (R,R′ = i-C3H7 (6); R = i-C3H7, R′ = CH3 (7); R,R′ = CH3 (8))} have been synthesized. Activated by Al(i-Bu)3, complex 6 shows very poor activity for the polymerization of ethylene at one bar ethylene pressure, whereas, 7 and 8 exhibit much higher activity than mononuclear iron catalysts {[ArNC(Me)C5H3N(Me)CNAr′]FeCl2 (Ar,Ar′ = 2,6-C6H3-i-Pr (9); Ar = 2,6-C6H3-i-Pr2, Ar′ = 2,6-C6H3–Me2 (10); Ar,Ar′ = 2,6-C6H3–Me2 (11))}. The molecular weight (Mw) of PE produced by 7 and 8 are in the range 13.2–46.0 × 104 and much higher than those produced by mononuclear iron catalysts 9 and 10. GPC results demonstrate that 7 and 8 yield PE with a broad/bimodal molecular weight distribution (MWD). In contrast, 9 and 10 yield PE with relatively narrow and unimodal MWD (4.26 and 3.55). Elevating the temperature and Al/Fe molar ratio will narrow the MWD of PE.