Tag strategy for separation and recovery

Variable-temperature NMR studies of soluble polymer-supported phosphine-silver complexes

The use of polymers as supports for organometallic catalysts has received wide attention. However, catalyst reactivity is sometimes altered as a consequence of catalyst immobilization by a polymeric ligand and such altered reactivity can complicate such supported catalysts' use. The results in this study show that heptane phase selectively soluble polyisobutylene (PIB)-bound phosphine ligands have essentially identical kinetic behavior when compared to electronically similar isobutyldiphenylphosphine analogues in phosphine coordination and exchange in silver(I) halide complexes. These studies used variable-temperature (31)P NMR spectroscopy to probe the silver-phosphine exchange processes for both AgI and AgCl complexes of these polymeric and low molecular weight phosphine ligands. The results show that the dynamic behavior of the PIB- and isobutyldiphenylphosphine-AgX complexes is nearly identical based on line-shape analysis of these (31)P NMR spectra as a function of temperature. Similar studies of more polar poly(ethylene glycol)triarylphosphine-bound AgX complexes and electronically analogous low molecular weight AgX complexes have similar behavior in variable-temperature (31)P NMR spectroscopy.

Multistep phase-switch synthesis by using liquid-liquid partitioning of boronic acids: productive tags with an expanded repertoire of compatible reactions

Tagging along: a system for phase-switch synthesis has been developed. The boronic acid functionality is used as a phase tag that complexes to sorbitol and facilitates compound transfer from an organic solvent to water at high pH. The phase tag can then be used in a productive reaction step to generate targeted products, thereby eliminating purification by silica gel chromatography.

Continuous flow based catch and release protocol for the synthesis of alpha-ketoesters

Using a combination of commercially available mesofluidic flow equipment and tubes packed with immobilised reagents and scavengers, a new synthesis of alpha-ketoesters is reported.

Fluorous Chemistry in Pittsburgh: 1996-2008

The article summarizes a lecture presented at the American Chemical Society Symposium for the 2008 Award for Creative Work in Fluorine Chemistry on April 7, 2008. A high level, historical overview of work in the fluorous field at the University of Pittsburgh is presented.

Dual functionalities of hydrogen-bonding self-assembled catalysts in chelation-assisted hydroacylation

A recyclable catalyst for chelation-assisted hydroacylation of an olefin with primary alcohol was developed using hydrogen-bonding self-assembled catalysts consisting of 2,6-diaminopyridine and barbiturate phosphine-rhodium(I) complex. Upon heating, these two catalysts act as homogeneous catalysts due to cleavage of the hydrogen bond, and these associate to form supramolecular assemblies via hydrogen bonding that can be separated from immiscible product phase upon cooling after the reaction.

A new approach to anodic substitution reaction using acoustic emulsification

We have developed a novel electrolytic system for anodic substitution reactions using acoustic emulsification. This new system involves the generation of a carbocation by anodic oxidation of a substrate, and then its reaction with a nucleophile droplet formed by ultrasonication. In this system, even if the oxidation potential of the nucleophile is lower than that of the substrate, the substrate was predominantly oxidized to give the corresponding cation intermediate because the nucleophile phase, which was insoluble in the electrolytic medium, was electro-inactive. In addition, the overoxidation of the desired products was considerably suppressed by the extraction of products from the electrolyte solution into the nucleophile phase. As a result, the anodic substitution reaction of several carbamates with allyltrimethylsilane was carried out to provide the corresponding products in good to moderate yields.

Solid Phase Synthesis of 4,5-disubstituted 1,2,4-triazol-3-one Derivatives from resin-bound Acylhydrazines

A new strategy for solid-phase synthesis of 4,5-disubstituted 2,4-dihydro-3 H-1,2,4-triazol-3-ones has been developed. The 4-substituted 5-(4-hydroxyphenyl)-1,2,4-triazol-3-one derivatives were synthesised from resin-bound acylhydrazines in several steps, in good overall yields and purity.

High-load, oligomeric monoamine hydrochloride: Facile generation via ROM polymerization and application as an electrophile scavenger

A new high-load, oligomeric monoamine hydrochloride (OMAm*HCl) derived from ring-opening metathesis polymerization (ROMP) of norbornene methylamine is reported. This oligomeric amine has been shown to be an effective scavenger of acid chlorides, sulfonyl chlorides and isocyanates. The reagent can be synthesized in a straightforward protocol from the Diels-Alder reaction of dicyclopentadiene (DCPD) 1 with allylamine (neat), formation of the corresponding ammonium salt and subsequent ROM polymerization to afford the desired oligomeric ammonium salts.

Sustainable Concepts in Olefin Metathesis

Ruthenium-catalyzed olefin metathesis reactions represent an attractive and powerful transformation for the formation of new carbon-carbon double bonds. This area is now quite familiar to most chemists as numerous catalysts are available that enable a plethora of olefin metathesis reactions. Nevertheless, with the exception of uses in polymerization reactions, only a limited number of industrial processes use olefin metathesis. This is mainly due to difficulties associated with removing ruthenium from the final products. In this context, a number of studies have been carried out to develop procedures for the removal of the catalyst or the products of catalyst decomposition, however, none are universally attractive so far. This situation has resulted in tremendous activity in the area dealing with supported or tagged versions of homogeneous catalysts. This Review summarizes the numerous studies focused on developing cleaner ruthenium-catalyzed metathesis processes.

m-Iodosylbenzoic acid - a convenient recyclable reagent for highly efficient aromatic iodinations

m-Iodosylbenzoic acid performs iodinations of arenes in the presence of iodine at room temperature in acetonitrile. Separation of pure products is conveniently achieved by scavenging any aryl iodide by ion exchange with IRA-900 (hydroxide form). The reduced form of the reagent, m-iodobenzoic acid, can be easily recovered from the ion exchange resin or from the basic aqueous solution by simple acidification with HCl.

Tagged phosphine reagents to assist reaction work-up by phase-switched scavenging using a modular flow reactor

The use of three orthogonally tagged phosphine reagents to assist chemical work-up via phase-switch scavenging in conjunction with a modular flow reactor is described. These techniques (acidic, basic and Click chemistry) are used to prepare various amides and tri-substituted guanidines from in situ generated iminophosphoranes.

Oligomeric Benzylsulfonium Salts: Facile Benzylation via High-Load ROMP Reagents

The development of high-load, oligomeric benzylsulfonium salts, generated via ring-opening metathesis polymerization, and their utility in facile benzylations of various nucleophiles is reported. These oligomeric sulfonium salts exist as free-flowing powders and are stable at room temperature. After the benzylation event, purification is attained via simple dry load/filtration, followed by solvent removal to deliver products in excellent yield and purity.

Fully automated flow-through synthesis of secondary sulfonamides in a binary reactor system

A fully automated flow-through process for the production of secondary sulfonamides is presented. Primary sulfonamides were monoalkylated using a two-step "catch and release" protocol to generate library products of high purity. The automated flow synthesis platform incorporates four independent reactor columns and is able to perform automated column regeneration. A 48-member sulfonamide library was prepared as two 24-member sublibraries, affording library compounds in good yields and high purities without the need for further column chromatographic purification.

Use of Fluorous Chemistry in the Solubilization and Phase Transfer of Nanocrystals, Nanorods, and Nanotubes

Fluorous chemistry, involving the use of a fluorous label for the functionalization of a substrate and a fluorous solvent for extraction of the functionalized substrate, is shown to be effective in solubilizing gold and CdSe nanoparticles in a fluorous medium, through phase transfer from an aqueous or a hydrocarbon medium. While these nanoparticles were functionalized with a fluorous thiol, single-walled carbon nanotubes and ZnO nanorods could be solubilized in a fluorous medium by reacting them with a fluorous amine. Fluorous chemistry enables the solubilization of the nanostructures in the most nonpolar liquid medium possible.

Fluorous nanodroplets structurally confined in an organopalladium sphere

The distinct properties of fluorous phases are practically useful for separation, purification, and reaction control in organic synthesis. Here, we report the formation of a liquid-like fluorous droplet, composed of 24 perfluoroalkyl chains confined in the interior of a 5-nanometer-sized, roughly spherical shell that spontaneously assembled in solution from 12 palladium ions and 24 bridging ligands. Crystallographic analysis confirmed the rigid shell framework and amorphous interior. Perfluoroalkanes can dissolve in this well-defined fluorous phase, whereas they can hardly dissolve in a surrounding polar organic solution, and their solubility (up to approximately eight perfluoroalkane molecules per spherical complex) can be finely controlled by tuning the length of perfluoroalkyl chains tethered to the shell.