Influence of type and positioning of N-aryl substituents on vinyl polymerization of norbornene by Ni(II) α-diimine complexes

Abstract

Effects of structural variations of the diimine ligand on catalyst activities for vinyl polymerization of norbornene (NB) have been investigated by a series of Ni(II) α-diimine catalysts of the general formula: [{ArN=C(Ac)-C(Ac)=NAr}]NiBr 2 (Ac=acenaphthyl) (Cat(H), Ar=C 6 H 5 ; 6 H 2 Me 3 ). In situ reactions with methylaluminoxane generated the active catalysts, and they showed good activity towards NB polymerizations. As indicated by relatively higher activities of Cat(H) and Cat(3,5-Me), it can be generalized that catalysts having 2,6-substituents are less active due to steric interaction between monomer and substituents. In addition, electron donating methyl groups at 2-, 4-or 6-position on the N-aryl have a con effect and that at 3,5-position has a pro effect.

Highly active and stereospecific polymerizations of 1,3-butadiene by using bis(benzimidazolyl)amine ligands derived Co(II) complexes in combination with ethylaluminum sesquichloride

“…In case of 3b/EASC system, methyl substitution on N-atom of benzimidazolyl group with its electron donating inductive effect may direct the electrons towards the active metal center making it less electropositive, as indicated by its comparatively lower activity. Similar trend of activity increase with a net increase in electropositivity of metal center was observed in our previous report involving the polymerization of norbornene by Ni(II) diimine catalysts [22]. BD polymerization conducted with CoCl 2 /EASC system under identical reaction conditions produced PBDs with a significantly lower conversion, elucidating the importance of ligand influence to the active center (Entry 4 in Table 1).…”

Nickel(II) Complexes with Three-Dimensional Geometry α-Diimine Ligands: Synthesis and Catalytic Activity toward Copolymerization of Norbornene

“…Especially, it was far higher than the activities of conventional Ni diimines (10 5 g of polymer/((mol of Ni) h)). 56,57 Large steric substituents on the aryl rings can effectively shield the axial plane of the central metal and suppress the side reaction of chain growth. Furthermore, with an increasing number of electron-donating substituents on the aryl rings, C3 demonstrated higher activity in comparison to C1, while complex C4 with an electron-withdrawing para substituent on the aryl ring exhibited the lowest catalytic activity.…”

Synthesis and X-ray crystallographic characterization of substituted aryl imines

“…Specifically, transition metal catalysts containing coordinated a-diimine 3 have been used for the synthesis of epoxides [18], N-arylpyrroles [19], hetero-Diels-Alder adducts [19], aniline from the reduction of nitrobenzene [20], and allylic amines [19,21]. Coordination of a-diimine 2 to nickel(II) gives a catalyst that can polymerize norbornene [22]. Additionally, complexes containing a-iminoketones have been shown to polymerize olefins [23] and phenylacetylene [24].…”