Electrophilic phenoxy-substituted phosphonium cations.

A family of electrophilic phenoxy-substituted phosphonium salts [(RO)P(CF)][B(CF)] (R = CH, 4-FCH, 2,4-FCH, CF) have been synthesized and their air stability was evaluated. Computations of the fluoride ion affinity and global electrophilicity index have been used to compare the electrophilicity of these phosphonium salts. The Lewis acidity of these phosphonium salts was probed computationally and experimentally in a Friedel-Crafts-type dimerization, hydrodefluorination, hydrosilylation, hydrodeoxygenation, and dehydrocoupling reactions.

Phosphine and carbene azido-cations: [(L)N] and [(L)N].

The cationic N-species [(-HCF)PN] () featuring a perfluoro-arene phosphonium group serves as a N-source in stoichiometric reactions with several Lewis bases (L) allowing for the stepwise formation of [(L)N] and [(L)N] cations (L = phosphine, carbene) with liberation of (-HCF)P. X-Ray diffraction analysis and computational studies provide insight into the bonding in these remarkably stable azido-cations.

Electrophilic Fluorophosphonium Cations in Frustrated Lewis Pair Hydrogen Activation and Catalytic Hydrogenation of Olefins.

The combination of phosphorus(V)-based Lewis acids with diaryl amines and diaryl silylamines promotes reversible activation of dihydrogen and can be further exploited in metal-free catalytic olefin hydrogenation. Combined experimental and density functional theory (DFT) studies suggest a frustrated Lewis pair type activation mechanism.

Synthesis and Lewis acidity of fluorophosphonium cations.

A series of fluorophosphonium salts, [R3PF][X] (R = alkyl or aryl; X = FB(C6F5)3, [B(C6F5)4]), have been prepared by reactions of phosphine/borane frustrated Lewis pairs (FLPs) with XeF2 or difluorophosphoranes with [Et3Si][B(C6F5)4]. As the substituents bound to phosphorus become increasingly electron withdrawing, the corresponding fluorophosphonium salts are shown to be increasingly Lewis acidic. Calculations were also performed to determine the relative fluoride ion affinities (FIA) of these fluorophosphonium cations.

Boron perturbed click reactions prompt aromatic C-H activations.

The reaction of boron alkynes and boron azides leads to rare N3BC heterocycles resulting from aromatic C-H activation of benzene and toluene. While subsequent treatment with PMe3 gave the P-B adduct with the exocyclic boron, reaction with PtBu3 effected deprotonation of the heterocycle to give the corresponding phosphonium salt.

Inherent stability limits of intramolecular boron nitrogen Lewis acid-base pairs.

The reaction of (C(6)F(5))(2)BH (1) with N,N-dimethylallylamine (2), N,N-diethylallylamine (3) and 1-allylpiperidine (4) afforded the five-membered ring systems (C(6)F(5))(2)B(CH(2))(3)NR(2) (R = Me (5), Et (6)) and (C(6)F(5))(2)B(CH(2))(3)N(CH(2))(5) (7) with an intramolecular dative B-N bond. A different product was obtained from the reaction of (C(6)F(5))(2)BH (1) with N,N-diisopropylallylamine (8), which afforded the seven-membered ring system (C(6)F(5))(2)B(CH(2))(3)N(iPr)CH(Me)CH(2) (9) under extrusion of dihydrogen. All compounds were characterised by elemental analysis, NMR spectroscopy and single-crystal X-ray diffraction experiments.

Intramolecular Lewis acid-base pairs based on 4-ethynyl-2,6-lutidine.

The reaction of 4-ethynyl-2,6-lutidine, (2,6-Me(2))(4-HC≡C)C(5)H(2)N (2), with B(C(6)F(5))(3) afforded the zwitterion [(2,6-Me(2))(4-(C(6)F(5))(3)BC≡C)C(5)H(2)NH] (3) via a deprotonation pathway. By treatment of 2 with the group 13 trialkyls AlMe(3), AlEt(3), GaMe(3), GaEt(3) and InMe(3), metallation of the ethynyl group afforded compounds 4-8 under extrusion of the corresponding alkane. The resulting products were characterised by elemental analyses and NMR spectroscopy.

Bis(tetrafluorophenyl)borane.

The reaction of the Grignard reagent (p-C(6)F(4)H)MgBr with Me(2)SnCl(2) afforded the p-C(6)F(4)H transfer reagent Me(2)Sn(p-C(6)F(4)H)(2) (1). Subsequent reaction of 1 with BCl(3) led to the chloroborane (p-C(6)F(4)H)(2)BCl (2), which was converted to the borane [(p-C(6)F(4)H)(2)BH](2) (3) by treatment with the hydride source Me(2)SiHCl. By reaction of tetrafluoropyridine with i-PrMgCl followed by the in situ reaction with Me(2)SnCl(2), the stannane Me(2)Sn(C(5)F(4)N)(2) (4) could be obtained.

Reactions of substituted pyridines with electrophilic boranes.

The lutidine derivative (2,6-Me(2))(4-Bpin)C(5)H(2)N when combined with B(C(6)F(5))(3) yields a frustrated Lewis pair (FLP) which reacts with H(2) to give the salt [(2,6-Me(2))(4-Bpin)C(5)H(2)NH][HB(C(6)F(5))(3)] (1). Similarly 2,2'-(C(5)H(2)(4,6-Me(2))N)(2) and (4,4'-(C(5)H(2)(4,6-Me(2))N)(2) were also combined with B(C(6)F(5))(3) and exposed to H(2) to give [(2,2'-HN(2,6-Me(2))C(5)H(2)C(5)H(2)(4,6-Me(2))N][HB(C(6)F(5))(3)] (2) and [(4,4'-HN(2,6-Me(2))C(5)H(2)C(5)H(2)(2,6-Me(2))N] [HB(C(6)F(5))(3)] (3), respectively. The mono-pyridine-N-oxide 4,4'-N(2,6-Me(2))C(5)H(2)C(5)H(2)(2,6-Me(2))NO formed the adduct (4,4'-N(2,6-Me(2))C(5)H(2)C(5)H(2)(2,6-Me(2))NO)(B(C(6)F(5))(3)) (4) which reacts further with B(C(6)F(5))(3) and H(2) to give [(4,4'-HN(2,6-Me(2))C(5)H(2)C(5)H(2)(2,6-Me(2))NO)B(C(6)F(5))(3)] [HB(C(6)F(5))(3)] (5).

Chemically fixed p-n heterojunctions for polymer electronics by means of covalent B-F bond formation.

Widely used solid-state devices fabricated with inorganic semiconductors, including light-emitting diodes and solar cells, derive much of their function from the p-n junction. Such junctions lead to diode characteristics and are attained when p-doped and n-doped materials come into contact with each other. Achieving bilayer p-n junctions with semiconducting polymers has been hindered by difficulties in the deposition of thin films with independent p-doped and n-doped layers.