Electrophilic phenoxy-substituted phosphonium cations.

A family of electrophilic phenoxy-substituted phosphonium salts [(RO)P(C6F5)3][B(C6F5)4] (R = C6H5, 4-FC6H4, 2,4-F2C6H3, C6F5) 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.

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.

Phosphine and carbene azido-cations: [(L)N3]+ and [(L)2N3].

The cationic N3-species [(p-HC6F4)3PN3]+ (1) featuring a perfluoro-arene phosphonium group serves as a N3+-source in stoichiometric reactions with several Lewis bases (L) allowing for the stepwise formation of [(L)N3]+ and [(L)2N3]+ cations (L = phosphine, carbene) with liberation of (p-HC6F4)3P. X-Ray diffraction analysis and computational studies provide insight into the bonding in these remarkably stable azido-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.

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. Compounds 4 and 8 were crystallized from THF and were yielded as monomers with coordinated THF molecules. The gallium compound 7 could be crystallised from benzene and was afforded as coordination polymer. The structures of these three compounds (4·THF, 7 and 8·2THF) were determined by single-crystal X-ray diffraction experiments. The aluminium compounds 4 and 5 show redistribution reaction of their substituents.

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. Density functional theory (DFT) studies were performed to rationalise the different reaction mechanism for the formation of products 6 and 9. The bonding situation of compound 9 was analysed in terms of its electron density topology to describe the delocalised nature of a borane-enamine adduct.

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. However, this did not react with BCl(3). The resulting products were characterized by elemental analyses and NMR spectroscopy. Single crystal X-ray diffraction experiments were performed for compounds 1, 2 and 4. The crystal structure of the literature known compound Me(2)Sn(C(6)F(5))(2) (5) was determined and compared with structures of 1 and 4.

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). In a related sense, 2-amino-6-CF(3)-C(5)H(3)N reacts with B(C(6)F(5))(3) to give (C(5)H(3)(6-CF(3))NH)(2-NH(B(C(6)F(5))(3))) (6). Similarly, the species, 2-amino-quinoline, 8-amino-quinoline and 2-hydroxy-6-methyl-pyridine were reacted with B(C(6)F(5))(3) to give the products as (C(9)H(6)NH)(2-NHB(C(6)F(5))(3)) (7), (C(9)H(6)N)(8-NH(2)B(C(6)F(5))(3)) (8) and (C(5)H(3)(6-Me)NH)(2-OB(C(6)F(5))(3)) (9), respectively; while 2-amino-6-picoline, 2-amino-6-CF(3)-pyridine, 2-amino-quinoline, 8-amino-quinoline and 2-hydroxy-6-methyl-pyridine react with ClB(C(6)F(5))(2) to give the species (C(5)H(3)(6-R)NH)(2-NH(ClB(C(6)F(5))(2))) (R = Me (10), R = CF(3) (11)) (C(9)H(6)NH)(2-NH(ClB(C(6)F(5))(2))) (12), (C(9)H(6)N)(8-NH(2)ClB(C(6)F(5))(2)) (13) and (C(5)H(3)(6-Me)NH)(2-OClB(C(6)F(5))(2)) (14), respectively. In a similar manner, 2-amino-6-picoline and 2-amino-quinoline react with B(C(6)F(5))(2)H to give (C(5)H(3)(6-Me)NH)(2-NH(HB(C(6)F(5))(2))) (15) and (C(9)H(6)NH)(2-NH(HB(C(6)F(5))(2))) (16). The corresponding reaction of 8-amino-quinoline yields (C(9)H(6)N)(8-NHB(C(6)F(5))(2)) (17). In a similar fashion, reaction of 2-amino-6-CF(3)-pyridine resulted in the formation of (18) formulated as (C(5)H(3)(6-CF(3))N)(2-NH(B(C(6)F(5))(2)). Finally, treatment of 15 with iPrMgCl gave (C(9)H(6)N)(2-NH(B(C(6)F(5))(2))) (19). Crystallographic studies of 1, 2, 4, 6, 7, 10, 11, 12 and 15 are reported.

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. Here we report on how to achieve permanently fixed organic p-n heterojunctions by using a cationic conjugated polyelectrolyte with fluoride counteranions and an underlayer composed of a neutral conjugated polymer bearing anion-trapping functional groups. Application of a bias leads to charge injection and fluoride migration into the neutral layer, where irreversible covalent bond formation takes place. After the initial charging and doping, one obtains devices with no delay in the turn on of light-emitting electrochemical behaviour and excellent current rectification. Such devices highlight how mobile ions in organic media can open opportunities to realize device structures in ways that do not have analogies in the world of silicon and promise new opportunities for integrating organic materials within technologies now dominated by inorganic semiconductors.