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Tris(pentafluoroethyl)difluorophosphorane and N ‐Heterocyclic Carbenes: Adduct Formation and Frustrated Lewis Pair Reactivity
Author(s) -
Föhrenbacher Steffen A.,
Zeh Vivien,
Krahfuss Mirjam J.,
Ignat'ev Nikolai V.,
Finze Maik,
Radius Udo
Publication year - 2021
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.202100183
Subject(s) - chemistry , adduct , steric effects , reactivity (psychology) , medicinal chemistry , phosphorane , frustrated lewis pair , lewis acids and bases , phosphonium , phosphine , stereochemistry , tris , catalysis , organic chemistry , medicine , biochemistry , alternative medicine , pathology
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‐di‐organyl‐imidazolin‐2‐ylidene) and phosphines are reported. For NHCs with small alkyl substituents at nitrogen ( R =Me, n Pr, i Pr) 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‐(2,6‐di‐ iso ‐propylphenyl)‐imidazolin‐2‐ylidene) ( 1 i ) and t Bu 2 Im (1,3‐di‐ tert ‐butyl‐imidazolin‐2‐ylidene) ( 1 j ) afforded the a NHC adducts 3 i and 3 j ( a denotes “abnormal” NHC coordination via a backbone carbon atom). The use of t BuMeIm (1‐ tert ‐butyl‐3‐methyl‐imidazolin‐2‐ylidene) ( 1 m ) led to partial decomposition of the NHC and formation of the salt [ t BuMeIm−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 t Bu 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−(CH 2 ) 4 O−PF 2 (C 2 F 5 ) 3 6 i – k . Furthermore, the deprotonation of the weak C−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)] − ( 7 ), [PF 2 (C 2 F 5 ) 3 (OC(=CH 2 )CH 3 )] − ( 8 ) and [PF 2 (C 2 F 5 ) 3 (CH 2 CO 2 Et)] − ( 9 ).