Further Development of Weakly Coordinating Cations: Fluorinated Bis(triarylphosphoranylidene)iminium Salts

Abstract

So far unknown bis(triarylphosphoranylidene)iminium cations [PPN] with one fluorine atom in para ([PPN-1 ] ), two in meta ([PPN-2 ] ), or three in para and meta positions of the phenyl rings ([PPN-3 ] ) were obtained by a newly developed one-pot reaction. These halogenated [PPN] cations were characterized by IR and Raman spectroscopy in comparison with quantum-chemical calculations, ESI mass spectrometry, NMR spectroscopy, and single-crystal X-ray diffraction. To assess their quality as weakly coordinating cations and the associated ability to stabilize labile anions, the electrostatic potential and fluoride-ion affinity were calculated and compared with those of the unsubstituted and so far unknown perfluorinated [PPN-5 ] cations.

Molybdenum(VI) Bis(imido) Complexes: From Frustrated Lewis Pairs to Weakly Coordinating Cations

“…Thus, bulky cations with high charge distribution also favor ion separation, which may stabilize reactive anions leading to higher reactivity in catalytic applications. [48,49] The higher reactivity of 2 b compared to 2 a in the insertion of benzaldehyde into the BÀ H bond may possibly be explained similarly. The cation in 2 b is significantly more sterically demanding due to the additional CF 3 groups in the imino phenolate ligands.…”

New Perspectives in the Noble Gas Chemistry Opened by Electrophilic Anions

“…Even less F-substituted arylxenon derivatives (Aryl = 2,6-F 2 C 6 H 3 , 2-FC 6 H 4 , 4-FC 6 H 4 ) were found to be stable at temperatures slightly below 0 • C, when inert tetrafluoroborate [BF 4 ] − was used as a counterion (Naumann et al, 1993). In our case, we should look for bulky weakly coordinating cations ["weakly coordinating cations" is a rather recent concept complementary to the much older concept of "weakly coordinating anions"; see, for example (Price et al, 2009;Fischer et al, 2014;Moritz et al, 2015;Mann et al, 2018)], which do not contain any nucleophilic site that can attack the B-NG bond. Preferentially, we need to find a chemically inert, symmetric, bulky, and rigid cationic species that will be able to reliably separate [B 12 X 11 NG] − anions from each other in the solid phase.…”

Polybromide Dianions and Networks Stabilized by Fluorinated Bromo(triaryl)phosphonium Cations

“…As already mentioned [(C 6 H 5 ) 3 PBr][Br 7 ] was obtained by the reaction of triphenylphosphine with 5 equivalents of elemental bromine in the eutectic mixture of ionic liquids [C 10 MPyr]Br (C 10 MPyr = N-decyl-N-methylpyrrolidinium) and [C 4 MPyr][OTf ] (C 4 MPyr = N-butyl-N-methylpyrrolidinium; OTf = triflate). [11] In a similar approach but without using ionic liquids as a solvent we performed our reactions in neat bromine.…”

“…Besides, the amount of bromine, the structural motif depends especially on the employed cation. [10] This class of fluorinated weakly coordinating cations has not yet been used for the preparation of polyhalide systems. [7,8] Therefore the size of the polybromide anion and its properties can be drastically influenced by the cation.…”