Reactions of Alkyne and Nitrile Ligands in Tungsten (II) Complexes Public Deposited

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  • March 20, 2019
  • Beattie, Ross
    • Affiliation: College of Arts and Sciences, Department of Chemistry
  • The examination of light atom-light atom and metal-light atom multiple bonds is of great importance to the fields of both organic and inorganic chemistry. Group VI transition metals are particularly well suited to the investigation of these systems with extensive reports for both catalytic and stoichiometric systems. The [Tp′W(CO)(NCMe)(RC≡CH)]<sup>+</sup> cation provides a platform for the examination of the reactivity of the alkyne and nitrile fragments. When standard electrophiles are added to the neutral Tp′W(CO)(N=CHMe)(HC≡CH) complex they add to the nitrogen, forming cationic imine complexes [Tp′W(CO)(N(R)=CHMe)(HC≡CH)]<sup>+</sup>. This reactivity is unavailable for large electrophiles where sterics prevent access to nitrogen. When [CPh<sub>3</sub>][BF<sub>4</sub>] is added to Tp′W(CO)(N=CHMe)(HC≡CH) it rapidly oxidizes and couples to the 1-azavinylidene ligand at the β-carbon site forming the cationic imido complex [Tp′W(CO)(NCH(Me)CPh<sub>3</sub>)(HC≡CH)]<sup>+</sup>. The redox activity of the azavinylidene complex can be leveraged with the use of iodine oxidant to form the dimeric dicationic complex [(Tp′(CO)(HC≡CH)W)<sub>2</sub>(μ-NCH(Me)CH(Me)N)]<sup>2+</sup>. This dimerization occurs with complete diastereoselectivity to form the S,S,R,R complex. Deprotonating the azavinylidene complex forms the anionic acetylide [Tp′W(CO)(N=CHR)(C≡CR)]<sup>-</sup>. This anionic complex can also be dimerized through the azavinylidene β-carbon but selectivity is eroded. Deprotonating the neutral azavinylidene acetylene complex yields the anionic acetylide complex. By protonating this species Tp′W(CO)(N=CHMe)(C=CH<sub>2</sub>) can be observed by NMR spectroscopy. This vinylidene complex isomerizes at room temperature to the carbyne nitrile complex Tp′W(CO)(N≡CR)(CCH<sub>3</sub>). The carbyne α-carbon is protonated by strong acids, resulting in the formation of a carbene complex with an agostic interaction of the α-carbon proton. Reactions of nucleophiles with the nitrile alkyne cationic complexes [Tp′W(CO)(NCR)(R′C≡CH)]<sup>+</sup> are examined, revealing that both alkyne and nitrile ligands can be addition sites for nucleophilic attack. By adding nucleophiles to the β-carbon of the nitrile ligand a nucleophilic site could be created, allowing further intramolecular reactions to occur where the functionalized nitrile ligand attacks the bound alkyne. This is observed for [Tp′W(CO)(OC(NH<sub>2</sub>)Ph)(HC≡CH)]<sup>+</sup>, resulting from hydrolysis and rearrangement of the benzonitrile ligand. By treating this complex with excess base in the presence of water, the release of N-vinylbenzamide is observed demonstrating the intramolecular coupling of the two ligands. Similar reactivity is observed for the imine cationic complex [Tp′W(CO)(N(Me)=CHMe)(HC≡CH)]<sup>+</sup>.
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  • In Copyright
  • Meek, Simon
  • Templeton, Joseph
  • Brookhart, Maurice
  • Miller, Alexander
  • Schauer, Cynthia
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2016

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