The synthesis and characterization of Lewis acid/base adducts between tris(pentafluoroethyl)difluorophosphorane PF 2 (C 2 F 5 ) 3 and selected N-heterocyclic carbenes (NHCs) R 2 Im (1,3-diorganyl-imidazolin-2-ylidene) and phosphines are reported. For NHCs with small alkyl substituents at nitrogen (R=Me, nPr, iPr) the adducts NHC • PF 2 (C 2 F 5 ) 3 (2 a-h) were isolated. The reaction with the sterically more demanding NHCs Dipp 2 Im (1,3-bis-(2,6di-iso-propylphenyl)-imidazolin-2-ylidene) (1 i) and tBu 2 Im (1,3di-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 tBuMeImto partial decomposition of the NHC and formation of the salt [tBuMeImÀ H][MeIm • PF 2 (C 2 F 5 ) 3 ] (4 m). The phosphorane PF 2 (C 2 F 5 ) 3 forms adducts with PMe 3 but does not react with PPh 3 or PCy 3 . The mer-cis isomer of literature-known Me 3 P • PF 2 (C 2 F 5 ) 3 (5 a) was structurally characterized. Mixtures of the phosphorane PF 2 (C 2 F 5 ) 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 NHCÀ (CH 2 ) 4 OÀ PF 2 (C 2 F 5 ) 3 6 i-k. Furthermore, the deprotonation of the weak CÀ H acids CH 3 CN, acetone, and ethyl acetate was achieved, which led to the formation of the corresponding imidazolium salts and the phosphates [PF 2 (C 2 F 5 ) 3 (CH 2 CN)] À (7), [PF 2 (C 2 F 5 ) 3 (OC(=CH 2 )CH 3 )] À (8) and [PF 2 (C 2 F 5 ) 3 (CH 2 CO 2 Et)] À (9).