James Mack

Mechanochemistry: opportunities for new and cleaner synthesis

The aim of this critical review is to provide a broad but digestible overview of mechanochemical synthesis, i.e. reactions conducted by grinding solid reactants together with no or minimal solvent. Although mechanochemistry has historically been a sideline approach to synthesis it may soon move into the mainstream because it is increasingly apparent that it can be practical, and even advantageous, and because of the opportunities it provides for developing more sustainable methods. Concentrating on recent advances, this article covers industrial aspects, inorganic materials, organic synthesis, cocrystallisation, pharmaceutical aspects, metal complexes (including metal-organic frameworks), supramolecular aspects and characterization methods. The historical development, mechanistic aspects, limitations and opportunities are also discussed (314 references).

Solvent-free Sonogashira coupling reaction via high speed ball milling

Herein, we report on the solvent-free Sonogashira reaction utilizing high speed ball milling. Sonogashira coupling of a variety of para substituted aryl halides were performed with trimethylsilylacetylene or phenylacetylene. We observed that iodo and bromo substituted aromatics successfully undergo Sonogashira coupling. However, chloro and fluoro substituted aryl compounds were unreactive. Conducting the coupling reaction in the absence of copper iodide led to low yields. Alternately, if the reaction is conducted with a copper ball in a copper vial in lieu of copper iodide, the coupling product is observed in high yields. This demonstrates the first report on the use of the vial and ball material as a catalyst in a ball milled chemical reaction.

Rate enhancement of the Morita–Baylis–Hillman reaction through mechanochemistry

Through the novel technique of high speed ball milling we were able to generate Baylis–Hillman products in as little as 0.5 hours. This represents one of the fastest methods of Baylis–Hillman reactions under neat conditions. Upon analysis of various catalysts we found 1,4-diazabicyclo[2.2.2]octane to be the catalyst that led to the highest product yields in the shortest reaction time.

Scratching the catalytic surface of mechanochemistry: a multi-component CuAAC reaction using a copper reaction vial

Herein we report the first copper vial catalysed CuAAC reaction. Under solvent-free mechanochemical conditions the reaction is complete in as little as 15 minutes and the triazole product isolated straight from the reaction vial with no further purification.

The development of corannulene-based blue emitters

Novel blue emitters were synthesized based on the fullerene fragment corannulene. 1,2- bis(corannulenylethynyl)benzene and 1,4-bis(corannulenylethynyl)benzene were designed, synthesized, and shown to exhibit significant red shifts in their absorption spectra as compared to that of the parent corannulene. Photoluminescence studies show both 1,2- bis(corannulenylethynyl)benzene and 1,4- bis(corannulenylethynyl)benzene gives enhanced blue luminescence compared to the parent corannulene structure. 1,4-bis(corannulenylethynyl)benzene was observed to give intense blue luminescence when excited at 400 nm. DFT and TD-DFT calculations were performed and shown to be consistent with the observed experimental results.

An environmentally benign solvent-free Tishchenko reaction

Herein, we describe the solvent-free ball milling Tishchenko reaction. Using high speed ball milling and a sodium hydride catalyst, the Tishchenko reaction was performed for aryl aldehydes in high yields in 0.5 hours. The reaction is not affected by the type of ball bearing used and can be successful when conducted in a liquid nitrogen environment.

Freedom: a copper-free, oxidant-free and solvent-free palladium catalysed homocoupling reaction

Herein, we describe a copper-free, oxidant-free, solvent-free homocoupling reaction using a palladium catalyst under mechanochemical conditions. We extended the methodology to palladium catalyst on solid support which showed a different reactivity and different product ratios from the non-supported catalyst. We were able to recycle the polymer supported catalyst for 5 cycles.

The first solvent-free method for the reduction of esters

Utilizing the novel technique of high-speed ball milling, we herein report the first solvent-free reduction of esters.

Comparison of shaking versus baking: further understanding the energetics of a mechanochemical reaction

Using a mechanically driven Diels–Alder reaction we were able to characterize the chemical energetics of a SPEX 8000M mixer/mill. Our results demonstrate that the conditions produced by this type of mill are similar to those produced when performing the same reaction at 90 °C in solution. Discrete element models and in situ temperature logging were used to analyse the energetics of this system. These models indicate that the yields obtained using a SPEX 8000M mill are best correlated to the velocity of the media and number of non-zero force collisions.

Free-electron attachment to coronene and corannulene in the gas phase

Electron attachment to the polyaromatic hydrocarbons coronene and corannulene is studied in the electron energy range of about 0-14 eV using a high-resolution crossed electron-neutral beam setup. The major anions observed are the parent anions peaking at about 0 eV with cross sections of 3.8 x 10(-20) and 1 x 10(-19) m(2), respectively. The only fragment anions formed in coronene and corannulene are the dehydrogenated coronene and corannulene anions. Other anions observed in the negative mass spectra at about 0 eV can be ascribed to impurities of the sample. High-level quantum-mechanical studies are carried out for the determination of electron affinities, hydrogen binding energies, and structures of both molecules. The behavior of coronene and corannulene upon electron attachment is compared with that of other polyaromatic hydrocarbons studied previously.