Chemistry of Alkylnickel Complexes. Preparation and Properties of Alkylnickels with Tertiary Phosphine Ligands
Nickel complexes with metal-to-carbon bond are generally regarded as the active species in various nickel-catalyzed organic reactions such as polymerization, oligomerization, hydr9genation, isomerization and isotopic hydrogen exchange of olefins.1 Pertinent information regarding the mechanisms of these nickel-catalyzed reactions is expected to be gained by studying the behavior of the isolated alkylnickel complexes. Alkylnickel complexes without other ligand may be obtained in special cases,2 but the use of appropriate stabilizing ligands often gives more stable alkylnickel complexes which are suitable for studying the chemistry of these alkyls.3–5 Among various approaches for obtaining alkylnickel complexes the alkylation of nickel acetylacetonate with dialkylaluminum monoethoxide in the presence of ligands has been found to provide the most convenient route. Evidently the alkylation proceeds through stepwise exchange reactions of the acetylacetonato ligands with the alkyl group of the alkylaluminum compound with the formation of an intermediate having both alkyl and acetylacetonato ligands. In fact alkylnickel complexes of this type have been obtained by employment of a suitable stabilizing ligand and by carrying out the alkylation under mild conditions,6,7 and the formations of other alkyl(acetylacqtonato) and hydrido(acetylacetonato) complexes have been reported.8,9 The alkyl(acetylacetonato) intermediates may be further alkylated affording dialkylnickel complexes which are sometimes further reduced to zero valent nickel complexes by splitting of the alkyl-nickel bonds.
KeywordsNickel Complex Aluminum Component Tertiary Phosphine Alkyl Aluminum Triethyl Phosphine
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