Abstract
The chelate 1,2-bis(imine)nickel(butadiene) complex 4a (chelate ligand derived from condensation of biacetyl with 2,6-diisopropylaniline) adds the strong Lewis acid B(C 6F 5) 3 at the terminal carbon atom of the butadiene ligand to yield the dipolar substituted π-allyl-type betaine complex (lig)Ni[η 3-C 3H 4-CH 2B(C 6F 5) 3] ( Z- 6a). At 90 °C the kinetically formed product equilibrated with its E- 6a isomer. Similarly, 4a adds the boron Lewis acid (pyrrolyl)B(C 6F 5) 2 to yield the corresponding neutral dipolar π-allyl betaine complex Z- 7a, that slowly equilibrated with E- 7a over several hours at ambient temperature. Protonation of the butadiene ligand of complex 4a was achieved by treatment with the neutral Brønsted acid (2H-pyrrol)B(C 6F 5) 3 to yield the [(lig)Ni(η 3-crotyl) +][(pyrrolyl)B(C 6F 5) 3 −] salt 9a ( Z-/ E- 9a ratio=90:10 upon preparation). At 298 K this salt rearranged to a 5:95 mixture of Z- 9a/ E- 9a with a Gibbs activation energy of Δ G ‡ (298 K)=22.3±0.2 kcal mol −1. Complex 4a added [Ph 3C +] to the butadiene ligand to yield the salt [(lig)Ni(η 3-C 3H 4-CH 2CPh 3) +][B(C 6F 5) 4 −] ( Z- 12a), that proved isomerically stable under the applied reaction conditions. Similar reactions were carried out starting from the acenaphthylene 1,2-dione derived chelate bis(imine)Ni(butadiene) complex 4b. The systems 6, 7, 9 and 12 were found to be active ethene polymerization catalysts in the presence of Al( i-Bu) 3.
Published Version
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