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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380 Scopus citations

Abstract

The organolanthanides (Cp'2MH)2Cp’ = η5-(CH35C5, M = La, Nd, Sm, and Lu, and (Me2SiCp“2MH)2Cp” η5-(CH34C5, 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 > Me2SiCp2Lu > Cp'2La > Me2SiCp2Sm > Me2SiCp”2Nd, with N1for the most active catalyst exceeding 120 000 h-1at 25 °C and 1 atm of H2. Under the conditions employed, the rate law is v ∝ [olefin]°[Lanthanide] [H2] suggesting rapid, exothermic Lanthanide-H/olefin addition and rate-limiting M-C hydrogenolysis. When D2uptake 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-d2under D2in a non-mass-transport-limited regime) obeys the rate law v [olefin] [Lanthanide]1/2[H2]°, suggesting rate-limiting Lanthanide-H/olefin addition. For Cp’2Lu, the rate law is v ∝ [olefin] [lanthanide] [H2]°, 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]°[Lanthanide][H2] (3-hexyne → cis-3-hexene) and v ∝ [olefin] [Lanthanide] 1/2[H2]° (m-3-hexane ∝ n-hexane) except for (Cp'2LuH)2where v ∝ [olefin] [Lanthanide] [H2]°. 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 (US)
Pages (from-to)8111-8118
Number of pages8
JournalJournal of the American Chemical Society
Volume107
Issue number26
DOIs
StatePublished - Dec 1985

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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