Structural preferences of cyclopentadienyl and indenyl rings in iridium(I) carbene complexes

Martina Prinz, Luís F. Veiros, Maria José Calhorda, Carlos C. Romão, Eberhardt Herdtweck, Fritz E. Kühn, Wolfgang A. Herrmann

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22 Citations (Scopus)

Abstract

Cleavage of the [Ir(η 4 -COD)Cl] 2 dimer in the presence of the corresponding imidazolium salts and the strong base tBuO - leads to the formation of Ir(I) derivatives of N-heterocyclic carbenes. When halide is replaced by NaCp, a mixture of [Ir(η 4 -COD)(NHC R )(η 1 -Cp)] and [Ir(η 2 -COD)(NHC R )(η 5 -Cp)] is obtained. The latter is favored for R = Cy, while the former predominates for R = Me. Conversely, [Ir(η 4 -COD)(NHC R )(η 1 -Ind)] is the only product of the reaction with NaInd, despite the R substituent. DFT/B3LYP calculations confirmed that the η 1 coordination mode of the ring gives rise to the most stable structures, namely square planar complexes of 5d 8 Ir(I). The energy of the 18 electron species containing η 2 -COD and η 5 -Ind or Cp is higher by 13 and 5 kcal mol -1 , respectively. The fluxional behaviour of indenyl, detected by NMR in the solutions of [Ir(η 4 -COD)(NHC R )(η 1 -Ind)], is associated to the low energy of the η 3 -Ind species required in the conversion process, and is not easily observed in the cyclopentadienyl derivatives, where a similar intermediate is disfavored.

Original languageEnglish
Pages (from-to)4446-4458
Number of pages13
JournalJournal Of Organometallic Chemistry
Volume691
Issue number21
DOIs
Publication statusPublished - 15 Oct 2006

Keywords

  • Cyclopentadienyl
  • DFT calculations
  • Heterocyclic carbenes
  • Indenyl
  • Iridium complexes
  • Ring hapticity

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