Well‐Defined Cationic Methallyl α‐Keto‐β‐Diimine Complexes of Nickel

Abstract

Complex considerations: The synthesis and characterization of a discrete cationic nickel–methallyl complex (see structure: Ni green, N blue, O red) provided insight into the propagating sites generated by using α‐keto‐β‐diimine–nickel olefin‐polymerization catalysts. The addition of Al(C6F5)3 led to carbonyl coordination to aluminum, further depletion of the electron density at the nickel center, and a substantial increase in reactivity towards ethylene.

Synthesis and structural characterization of a nickel(II) precatalyst bearing a β‐triketimine ligand and study of its ethylene polymerization performance using response surface methods

“…Thus, chain transfer is predominantly to aluminum, and not to monomer. No attempt was made to remove residual Me 3 Al from the MAO used, and it is known that chain transfer to Al is favored in the presence of Me 3 Al 21, 22. Yet.…”

“…Only most recently, through the incorporation of further functional groups which confer the ability to remotely modify the electronic properties of the metal center without significantly altering the steric environment, have activities competitive with α‐diimine complexes such as 4 been achieved. In the case of 6 , usage of an α‐keto‐β‐diketimine ligand framework makes it susceptible to O ‐coordination by Lewis acids, which can be used to activate the metal center through remote locations 21, 22. This generated catalysts with much‐improved activities of several hundred kg [(mol Ni) −1 h −1 bar −1 ],21 associated with much greater catalyst stability, including claims of living character at high temperatures 22.…”

“…In the case of 6 , usage of an α‐keto‐β‐diketimine ligand framework makes it susceptible to O ‐coordination by Lewis acids, which can be used to activate the metal center through remote locations 21, 22. This generated catalysts with much‐improved activities of several hundred kg [(mol Ni) −1 h −1 bar −1 ],21 associated with much greater catalyst stability, including claims of living character at high temperatures 22. In a similar vein, nickel precatalysts bearing ( N ‐imidoylamidine) ligands have recently been reported 23.…”

On the non-innocence of “Nacnacs”: ligand-based reactivity in β-diketiminate supported coordination compounds

“…The reaction of (BDI Ar,Me )PtMe 3 (Ar = 4-t Bu2,5-MeC 6 H 2 ) with O 2 affords a bicyclic peroxo species in which dioxygen is bound both to the metal centre and to the γ-carbon of the ligand backbone (Scheme 36top). 169,170 Compared to the analogous Ni β-diimine complexes, the presence of the carbonyl moiety leads to substantial increase in the catalytic activity; this is attributed to the attachment of Lewis acids to the carbonyl functionality in the cationic active species (Scheme 38). 131 A γ-Me substituted BDI derivative was synthesized in order to stabilize and isolate the peroxo reaction intermediate shown on Fig.…”

Pd and Ni complexes of a novel vinylidene β‐diketimine ligand: Their application as catalysts in Heck coupling and alkyne trimerization

“…Among these, Ni catalysts have advantages of being cheaper and having readily available reagents for complexation with a wide range of ligands. It has also been reported that β‐diketimine‐based Ni complexes can be used in polymerization reactions . Hence we became interested in synthesizing Pd and Ni complexes of modified β‐diketimine ligands.…”