Journal
EUROPEAN JOURNAL OF INORGANIC CHEMISTRY
Volume 2021, Issue 20, Pages 1941-1960Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/ejic.202100183
Keywords
C− H activation; Fluoro(perfluoroalkyl)phosphoranes; Frustrated Lewis Pairs; N-Heterocyclic Carbenes; N-Heterocyclic Carbene Adducts
Categories
Funding
- Julius-Maximilians-Universitat Wurzburg
- Merck KGaA (Darmstadt, Germany)
- Projekt DEAL
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The synthesis and characterization of Lewis acid/base adducts between PF2(C2F5)(3) and selected N-heterocyclic carbenes (NHCs) and phosphines were reported. The steric effects of different alkyl substituents on NHCs influenced the stability of the adducts, with larger substituents leading to partial decomposition.
The synthesis and characterization of Lewis acid/base adducts between tris(pentafluoroethyl)difluorophosphorane PF2(C2F5)(3) and selected N-heterocyclic carbenes (NHCs) R(2)Im (1,3-di-organyl-imidazolin-2-ylidene) and phosphines are reported. For NHCs with small alkyl substituents at nitrogen (R=Me, nPr, iPr) the adducts NHC . PF2(C2F5)(3) (2 a-h) were isolated. The reaction with the sterically more demanding NHCs Dipp(2)Im (1,3-bis-(2,6-di-iso-propylphenyl)-imidazolin-2-ylidene) (1 i) and tBu(2)Im (1,3-di-tert-butyl-imidazolin-2-ylidene) (1 j) afforded the aNHC adducts 3 i and 3 j (a denotes abnormal NHC coordination via a backbone carbon atom). The use of tBuMeIm (1-tert-butyl-3-methyl-imidazolin-2-ylidene) (1 m) led to partial decomposition of the NHC and formation of the salt [tBuMeIm-H][MeIm . PF2(C2F5)(3)] (4 m). The phosphorane PF2(C2F5)(3) forms adducts with PMe3 but does not react with PPh3 or PCy3. The mer-cis isomer of literature-known Me3P . PF2(C2F5)(3) (5 a) was structurally characterized. Mixtures of the phosphorane PF2(C2F5)(3) and the sterically encumbered NHCs tBu(2)Im, Dipp(2)Im, and Dipp(2)Im(H2) (1,3-bis-(2,6-di-iso-propylphenyl)-imidazolidin-2-ylidene) (1 k) showed properties of FLPs (Frustrated Lewis Pairs) as these mixtures were able to open the ring of THF (tetrahydrofuran) to yield NHC-(CH2)(4)O-PF2(C2F5)(3) 6 i-k. Furthermore, the deprotonation of the weak C-H acids CH3CN, acetone, and ethyl acetate was achieved, which led to the formation of the corresponding imidazolium salts and the phosphates [PF2(C2F5)(3)(CH2CN)](-) (7), [PF2(C2F5)(3)(OC(=CH2)CH3)](-) (8) and [PF2(C2F5)(3)(CH2CO2Et)](-) (9).
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