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UBC Theses and Dissertations

Transformations of cyclic olefins mediated by tungsten and molybdenum nitrosyl complexes Buschhaus, Miriam Sarah Anne

Abstract

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.

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