Printer vriendelijke versie

Double methane borylation

28 March 2016 - Coincidences do not exist

Interesting double paper header in this week's issue of the journal science, a methane borylation and a methane borylation! A University of Michigan team beat a University of Pennsylvania team by just 6 days! And as coincidences do not exist in chemical land this is worth investigating. Team Michigan (by the way 75% women compared to 0% women in team Penn) describes a methane borylation (link). Key inspiration: a 2005 paper by Hall/Hartwig on computations on methane borylation with pentamethylcyclopentadienyl ruthenium catalysts. Publications like these can sit around for 11 years but eventually they will get picked up. The experimental validation provided by the Michigan team looks like this: the reaction of methane in with bis(pinacolato)diboron in cyclohexane @150°C and @2500 kPa with 3 mole% of Bis(pentamethylcyclopentadienyl)ruthenium(II) (Cp*)2Ru will give a 99% yield of the mono borane adduct. The ratio of mono-substitution versus di-substitution is 10:1. Not a small feat as the researchers explain because although the C-H bonds in methane are the least sterically hindered, those in the boron reagent are more acidic and those in the solvent are most numerous. With a more realistic catalyst loading of 0.75% the yield drops to 52% but the selectivity increases.

And how did the Pennsylvania team (link) get their inspiration? They do not cite the 2005 Hall/Hartwig paper but a 2010 Hartwig review. They note that breaking the boron boron bond in diboron reagents provide an enthalpic driving force and also that many iridium catalysts are commercially available. Hence their optimised result: The reaction of methane with bis(pinacolato)diboron in cyclohexane @150°C and 3500 kPa catalysed with 0.5% cyclooctadiene iridium chloride dimer and DMPE gives a 52% yield. Exactly the same result as team Michigan but with much lower selectivity.

But since when do coincidences exist? One team member on the Penn team, Milton R. Smith III, happens to be a professor at the University of Michigan... So how well do Milton and team Michigan get along these days?


Energy storage on a large scale

26 March 2016 - Haber and Bosch again save the planet

Energy company Nuon announced today it will convert one of its gas power plants in The Netherlands into a ammonia / energy storage facility. The first in the world of this type (Link). This facility that goes by the name 'Magnum' opened in 2013 as a multi-fuel plant capable of processing gas, coal and biomass and is equipped with carbon dioxide capture infrastructure. It has never processed coal though and never will because today both coal and carbon dioxide injection are controversial. Hence the surprise re-purposing plan. Excess wind and solar energy is to be used to produce the ammonia (from nitrogen and water in the Haber-Bosch process) which is then stored and again burned at peak-electricity demand. The energy efficiency is about 42% but even then this business could be very lucrative.

Things to do with

11 March 2016 - Nano

Zhang2016.PNGThings to do with a fullerene. Things to do with water and a fullerene. Things to do with water inside a fullerene? Things to do with two water molecules inside a C70 fullerene! This must have been the sort of thinking that went on inside the head of Yasujiro Murata. 15 years ago he brought you endohedral hydrogen fullerene (H2@C60) in a delicate sequence of chemically opening-up a fullerene, stuffing hydrogen inside and closing-up again. In a recent Nature Chemistry article his group repeated this feat but now with water (Rui Zhang et al. DOI). C70 has an inner space of 3.7 by 4.6 Angstrom, large enough to accommodate this cargo. Once the cage was opened, it took 9000 atm of pressure of water in toluene for 40 hours @120°C to get water to enter the cage. After closing-up and work-up H20@C70 was separated from empty C60 by simple HPLC. X-ray diffraction showed that the water molecule was in a disordered state. In the related compound H20@C60 water was very much unmoveable. Could there be room for a double occupancy? Re-examination of the HPLC trace revealed the minor presence of (H2O)2@C70. This compound was not isolated (somewhere there is a rule that "synthesised" means "isolated"?) but is was possible to examine it by spectroscopy (NMR, IR). The dimer was found to rotate quickly at temperatures as low as -80°C. Interestingly even though there is room for 4 hydrogen bonds (in a kind of inverted triangular prism) just one was found to operate.