title: A well-defined model system for the chromium-catalyzed selective oligomerization of ethylene.
abstract: The chromium(I) dinitrogen complex [(i-Pr2Ph)2nacnacCr]2(μ-η(2):η(2)-N2) catalyzes the selective trimerization of ethylene to 1-hexene at ambient pressure and temperature, and in the absence of any cocatalyst. After the conversion of the substrate, the catalyst cleanly converts to another chromium(I) species, namely [(i-Pr2Ph)2nacnacCr]2(μ-η(2):η(2)-C2H4), which is not catalytically active. Binuclear metallacycles containing Cr(II) have been prepared as candidates for catalytically active intermediates; however they are not kinetically competent to explain the catalysis. Turning thus to mononuclear metallacycles featuring Cr(III), a chromacyclopentane, chromacyclopentene and chromacyclopentadiene have been prepared as models of catalytic intermediates. Of these, the latter also catalyzes the trimerization of ethylene. These results support the proposal that selective ethylene oligomerization catalysis involves an interplay between Cr(I) ethylene complexes and mononuclear Cr(III) metallacycles.
authors.affiliation: Department of Chemistry and Biochemistry, Center for Catalytic Science and Technology, University of Delaware, Newark, Delaware 19716, USA.
authors.forename: Wesley H
authors.initials: WH
authors.lastname: Monillas
authors.forename: John F
authors.initials: JF
authors.lastname: Young
authors.forename: Glenn P A
authors.initials: GP
authors.lastname: Yap
authors.forename: Klaus H
authors.initials: KH
authors.lastname: Theopold
mesh_terms: D002857:Chromium / Q000737:chemistry*; D005030:Ethylenes / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D058105:Polymerization
chemical_list: D005030:Ethylenes; D009942:Organometallic Compounds; D002857:Chromium; C036216:ethylene