Thermolysis of Cp*W(NO)(CH ₂CMe₃) ₂,CpW(NO)(CH ₂CMe₃)₂, Cp*W(NO)(CH₂SiMe₃)(η²-CPhCH₂), or Cp*W(NO)[CH(Ph)CH₂CH(nPr)CH₂]in cyclic olefins
results in the formation of ring-retaining oligomers having lengths up to dodecamers. The main
cyclohexene dimer is 3-cyclohexylcyclohexene. A small percentage of oligomers contain
neopentyl or CH=CHPh end groups. Turnover frequencies for the Cp*-tungsten precatalysts
range from 5.5 to 6.5 mol/h at 100 °C.
In room temperature solutions, Cp*Mo(NO)(CH₂CMe₃)₂ generates the alkylidene
intermediate [Cp*Mo(NO)(=CHCMe₃)], which couples with cyclic olefins to form cismetallacycles.
The isolable cyclopentene-derived cis-metallacycle, Cp*Mo(NO)[cis-η²
CH(CH₂)₃CHCHCMe₃], converts in the solid state to the allyl-hydride complex
Cp*Mo(NO)(H)(η³-CH(CH₂)3CCHCMe₃). With larger cyclic olefins (cyclohexene through
cyclooctene) the initial cis-metallacycles isomerize to trans-metallacycles of the form
Cp*Mo(NO)[trans-η²-CH(CH₂)nCHCHCMe₃] (n = 4, 5, 6), and these subsequently convert with
loss of dihydrogen to η⁴-diene complexes, Cp*Mo(NO)[η⁴-CHCH(CH₂)n-₁CCHCMe₃].
Thermolysis of the η⁴-diene complexes in cyclohexene results in decomposition of the
organometallic complex with small amounts of oligomer formation.
Thermolysis of Cp*W(NO)CH₂CMe₃)₂ in cyclic-olefm substrates generates the
alkylidene intermediate [Cp*W(N0)(=CHCMe₃)], which couples with cyclic olefins in a manner
analogous to the Cp*Mo-system. Tungsten trans-metallacycles are observed by ¹H NMR
spectroscopy, but the organometallic subsequently reacts further with loss of the coupled
neopentyl-cyclic olefin and coordination of two substrate molecules to form the putative
Cp*W(NO)(cyclic olefm)₂ complex. Two additional cyclooctene products are isolated, the 1,4-
diene Cp*W(N0)[η⁴-CHCH(CH₂)₅CHCCH(CH₂)₆] and the allyl hydride Cp*W(NO)(H)[η³-
CH(CH₂)₆CCCHCH(CH₂)₅], both containing two coupled cyclooctene molecules. A tungsten
cis-metallacycle forms with 2,5-dihydrofiiran, but a ring-opened alkoxy-allyl complex forms
with 3,4-dihydro-2H-pyran, and 1,2,3,6-tetrahydro-pyridine undergoes N -H bond activation to
afford an amido product. CpW(NO)(CH₂CMe₃)₂ produces some oligomers of cyclohexene, but
in all other reactions bimetallic decomposition pathways predominate.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:BVAU.2429/2844 |
| Date | 11 1900 |
| Creators | Buschhaus, Miriam Sarah Anne |
| Publisher | University of British Columbia |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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