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Published February 11, 2004 | Supplemental Material
Journal Article Open

Mechanistic Studies of the Ethylene Trimerization Reaction with Chromium−Diphosphine Catalysts: Experimental Evidence for a Mechanism Involving Metallacyclic Intermediates


A system for catalytic trimerization of ethylene utilizing CrCl_3(THF)_3 and a diphosphine ligand PNP^(OMe) [= (o-MeO-C_6H_4)_2PN(Me)P(o-MeO-C_6H_4)_2] has been investigated. The coordination chemistry of chromium with PNP^(OMe) has been explored, and (PNP^(OMe))CrCl_3 and (PNP^(OMe))CrPh_3 (3) have been synthesized by ether displacement from chromium(III) precursors. Salt metathesis of (PNP^(OMe))CrCl_3 with o,o'-biphenyldiyl Grignard affords (PNP^(OMe))Cr(o,o'-biphenyldiyl)Br (4). Activation of 3 with H(Et_2O)_2B[C_6H_3(CF_3)_2]_4 or 4 with NaB[C_6H_3(CF_3)_2]_4 generates a catalytic system and trimerizes a 1:1 mixture of C_2D_4 and C_2H_4 to give isotopomers of 1-hexene without H/D scrambling (C_6D_(12), C_6D_8H_4, C_6D_4H_8, and C_6H_(12) in a 1:3:3:1 ratio). The lack of crossover supports a mechanism involving metallacyclic intermediates. The mechanism of the ethylene trimerization reaction has also been studied by the reaction of trans-, cis-, and gem-ethylene-d_2 with 4 upon activation with NaB[C_6H_3(CF_3)_2]_4.

Additional Information

© 2004 American Chemical Society. Received 9 October 2003. Published online 15 January 2004. Published in print 1 February 2004. We thank Drs. Steven A. Cohen, Glenn Sunley, and Duncan F. Wass (BP) for helpful discussions and Michael W. Day and Lawrence M. Henling (Caltech) for assistance with single-crystal X-ray crystallographic studies. We are grateful to BP Chemicals for financial support.

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Supplemental Material - ja038968trom20031014_064147.cif

Supplemental Material - ja038968tsi20031118_024350.pdf


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