Highly reactive organolanthanides. A mechanistic study of catalytic olefin hydrogenation by bis(pentamethylcyclopentadienyl) and related 4f complexes

Gerald Jeske, Harald Lauke, Heiko Mauermann, Herbert Schumann, Tobin J Marks

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372 Citations (Scopus)

Abstract

The organolanthanides (Cp′2MH)2, Cp′ = η-(CH3)5C5, M = La, Nd, Sm, and Lu, and (Me2SiCp″2MH)2, Cp″ = η5-(CH3)4C5, M = Nd, Sm, and Lu are highly active catalysts for olefin hydrogenation. In the case of 1-hexene → n-hexane, activities decrease in the order Cp′2Lu > Cp′2Sm > Cp′2Nd > Me2SiCp″2Lu > Cp′2La > Me2SiCp″2Sm > Me2SiCp″2Nd, with Nt for the most active catalyst exceeding 120000 h-1 at 25°C and 1 atm of H2. Under the conditions employed, the rate law is v ∝ [olefin]0[Lanthanide] [H2] suggesting rapid, exothermic Lanthanide-H/olefin addition and rate-limiting M-C hydrogenolysis. When D2 uptake is not mass-transport-limited, the predominant product is hexane-1,2-d2. For all catalysts except (Cp′2LuH)2, cyclohexene hydrogenation (to yield predominantly cyclohexane-1,2-d2 under D2 in a non-mass-transport-limited regime) obeys the rate law v ∝ [olefin][Lanthanide]1/2[H2]0, suggesting rate-limiting Lanthanide-H/olefin addition. For Cp′2Lu, the rate law is v ∝ [olefin][lanthanide][H2]0, suggesting rate-limiting (Lu-H)2/olefin addition or that the hydride dimer is largely dissociated under these conditions. The relative activities are less than for 1-hexene and follow the order (Me2SiCp″2NdH)2 > (Me2SiCp″2SmH)2 > (Cp′2LaH)2 ≥ (Cp′2NdH)2 > (Me2SiCp″2LuH)2 ≥ (Cp′2SmH)2. Addition of THF significantly decreases the rate both of 1-hexene hydrogenation and (more so) cyclohexene hydrogenation. For all catalysts examined, 3-hexyne hydrogenation follows a two-stage rate law v ∝ [alkyne]0[Lanthanide][H2] (3-hexyne → cis-3-hexene) and v ∝ [olefin][Lanthanide]1/2[H2]0 (cis-3-hexane → n-hexane) except for (Cp′2LuH)2 where v ∝ [olefin] [Lanthanide] [H2]0. The rate laws and relative activity trends for trans-2-hexene and trans-3-hexene hydrogenation parallel those for 1-hexene, while cis-2-hexene behaves like cis-3-hexene. While the present olefin and acetylene hydrogenation catalysis can be understood largely on the basis of established or reasonably extrapolated organo-f-element reactivity and bond enthalpy patterns, the steps in the catalytic cycles must proceed with remarkably low activation energies and must be coupled with high efficiency.

Original languageEnglish
Pages (from-to)8111-8118
Number of pages8
JournalJournal of the American Chemical Society
Volume107
Issue number26
Publication statusPublished - 1985

ASJC Scopus subject areas

  • Chemistry(all)

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