Synthesis and X-ray structure determination of highly active Pd(II), Pd(I), and Pd(0) complexes of di(tert-butyl)neopentylphosphine (DTBNpP) in the arylation of amines and ketones.

The air-stable complex Pd(η(3)-allyl)(DTBNpP)Cl (DTBNpP = di(tert-butyl)neopentylphosphine) serves as a highly efficient precatalyst for the arylation of amines and enolates using aryl bromides and chlorides under mild conditions with yields ranging from 74% to 98%. Amination reactions of aryl bromides were carried out using 1-2 mol % Pd(η(3)-allyl)(DTBNpP)Cl at 23-50 °C without the need to exclude oxygen or moisture. The C-N coupling of the aryl chlorides occurred at relatively lower temperature (80-100 °C) and catalyst loading (1 mol %) using the Pd(η(3)-allyl)(DTBNpP)Cl precatalyst than the catalyst generated in situ from DTBNpP and Pd(2)(dba)(3) (100-140 °C, 2-5 mol % Pd). Other Pd(DTBNpP)(2)-based complexes, (Pd(DTBNpP)(2) and Pd(DTBNpP)(2)Cl(2)) were ineffective precatalysts under identical conditions for the amination reactions. Both Pd(DTBNpP)(2) and Pd(DTBNpP)(2)Cl(2) precatalysts gave nearly quantitative conversions to the product in the α-arylation of propiophenone with p-chlorotoluene and p-bromoanisole at a substrate/catalyst loading of 100/1. At lower substrate/catalyst loading (1000/1), the conversions were lower but comparable to that of Pd(t-Bu(3)P)(2). In many cases, the tri-tert-butylphosphine (TTBP) based Pd(I) dimer, [Pd(µ-Br)(TTBP)](2), stood out to be the most reactive catalyst under identical conditions for the enolate arylation. Interestingly, the air-stable Pd(I) dimer, Pd(2)(DTBNpP)(2)(µ-Cl)(µ-allyl), was less active in comparison to [Pd(µ-Br)(TTBP)](2) and Pd(η(3)-allyl)(DTBNpP)Cl. The X-ray crystal structures of Pd(η(3)-allyl)(DTBNpP)Cl, Pd(DTBNpP)(2)Cl(2), Pd(DTBNpP)(2), and Pd(2)(DTBNpP)(2)(µ-Cl)(µ-allyl) are reported in this paper along with initial studies on the catalyst activation of the Pd(η(3)-allyl)(DTBNpP)Cl precatalyst.

A general design platform for ionic liquid ions based on bridged multi-heterocycles with flexible symmetry and charge.

A conceptual design platform for new ionic liquids with variable heterocycles, bridges, symmetry, and charge was developed using simple alkylation, click, and ionic liquid chemistries and demonstrated with 1-(2-(5-tetrazolidyl)ethyl)-3-(5-1H-tetrazolyl)methylimidazolium and its conversion into room-temperature ionic liquids as cation or as anion.

Ionic liquids based on azolate anions.

Compartmentalized molecular level design of new energetic materials based on energetic azolate anions allows for the examination of the effects of both cation and anion on the physiochemical properties of ionic liquids. Thirty one novel salts were synthesized by pairing diverse cations (tetraphenylphosphonium, ethyltriphenylphosphonium, N-phenyl pyridinium, 1-butyl-3-methylimidazolium, tetramethyl-, tetraethyl-, and tetrabutylammonium) with azolate anions (5-nitrobenzimidazolate, 5-nitrobenzotriazolate, 3,5-dinitro-1,2,4-triazolate, 2,4-dinitroimidazolate, 4-nitro-1,2,3-triazolate, 4,5-dinitroimidazolate, 4,5-dicyanoimidazolate, 4-nitroimidazolate, and tetrazolate). These salts have been characterized by DSC, TGA, and single crystal X-ray crystallography. The azolates in general are surprisingly stable in the systems explored. Ionic liquids were obtained with all combinations of the 1-butyl-3-methylimidazolium cation and the heterocyclic azolate anions studied, and with several combinations of tetraethyl- or tetrabutylammonium cations and the azolate anions. Favorable structure-property relationships were most often achieved when changing from 4- and 4,5-disubstituted anions to 3,5- and 2,4-disubstituted anions. The most promising anion for use in energetic ionic liquids of those studied here, was 3,5-dinitro-1,2,4-triazolate, based on its contributions to the entire set of target properties.

Ionic liquid-based routes to conversion or reuse of recycled ammonium perchlorate.

New, potentially green, and efficient synthetic routes for the remediation and/or re-use of perchlorate-based energetic materials have been developed. Four simple organic imidazolium- and phosphonium-based perchlorate salts/ionic liquids have been synthesized by simple, inexpensive, and nonhazardous methods, using ammonium perchlorate as the perchlorate source. By appropriate choice of the cation, perchlorate can be incorporated into an ionic liquid which serves as its own electrolyte for the electrochemical reduction of the perchlorate anion, allowing for the regeneration of the chloride-based parent ionic liquid. The electrochemical degradation of the hazardous perchlorate ion and its conversion to harmless chloride during electrolysis was studied using IR and (35)Cl NMR spectroscopies.

Using ionic liquids to trap unique coordination environments: polymorphic solvates of ErCl3(OH2)(4).2([C2mim]Cl).

Two polymorphs of ErCl(3)(OH(2))(4).2([C(2)mim]Cl) solvates were isolated from the same solution of 1-ethyl-3-methylimidazolium chloride when HCl(aq) was added, while [C(2)mim](3)[ErCl(6)] was isolated without HCl addition, illustrating how ionic liquids can be used to trap unusual coordination environments in the solid state.

An intermediate for the clean synthesis of ionic liquids: isolation and crystal structure of 1,3-dimethylimidazolium hydrogen carbonate monohydrate.

1,3-Dimethylimidazolium-2-carboxylate and carbonic acid have been used to prepare a 1,3-dimethylimidazolium hydrogen carbonate salt by means of a Krapcho reaction. The ability to form hydrogen carbonate azolium salts allows for them to be used as precursors for fast, efficient, environmentally benign, and halide-free syntheses of many ionic liquids by a simple, acid-base reaction of virtually any acid (inorganic, organic, and organic noncarboxylic) with a pK(a) less than that of HCO(3) (-). Additionally, the kinetics of this reaction can be accelerated by employing catalytic amounts of DMSO (a traditional Krapcho solvent used in decarboxylation reactions) to catalyze the decarboxylation. The crystal structure of 1,3-dimethylimidazolium hydrogen carbonate monohydrate is the first example of an imidazolium-based hydrogen carbonate salt. There is a strong 2D hydrogen-bonded network with facially pi-stacked imidazolium cations located in the cavities created by this framework.