Chemical Science Blog

Highly active catalysts for manufacturing bulk and fine chemicals can be made by simply grinding metal acetate salts with pre-formed supports.

Heterogeneous catalysis is a key chemical manufacturing process and lies at the heart of green chemical processes. The use of catalysts can lead to greener reactions when compared to alternative routes. But many routes for making catalysts use halides as a starting point and the halides are difficult to remove from the final material.

UK scientists have prepared supported gold, palladium and gold-palladium catalysts by mixing the metal acetate precursors. The simple, reproducible and scalable preparation method ensures the catalysts prepared are halide free. They found that the removal of the halide from the preparation step and therefore from the final catalyst leads to a significant enhancement in performance compared to previously reported catalysts.

Link to journal article
Physical mixing of metal acetates: a simple, scalable method to produce active chloride-free bimetallic catalysts
S A Kondrat et al
Chem. Sci., 2012, DOI: 10.1039/c2sc20450a

Cyclic paraphenylenes (CPPs), first made in 2008, have potential roles in carbon nanotube synthesis as well as interesting optoelectronic properties and nano-sized cavities. Despite their potential, scientists haven’t explored them much for materials and nano applications because they’ve been really difficult to make at a reasonable scale – 10-15mg is typical – and they are expensive.

Now, scientists in the US have come up with a procedure to make 20g of a common intermediate within a week, which can be used to make gram quantities of cyclic paraphenylenes. They developed a macrocyclisation step that uses a much cheaper palladium source than before (ligand-free), reducing the cost significantly. They also report the first solid-state structure of the supramolecular complex between C60 and [10]CPP, illustrating the perfectly matched convex/concave pi-pi interactions (they describe it as a nanopeapod structure).

Link to journal article
Gram-Scale Synthesis and Crystal Structures of [8]- and [10]CPP, and the Solid-State Structure of C60@[10]CPP
J Xia, J W Bacon and R Jasti
Chem. Sci., 2012, DOI: 10.1039/c2sc20719b

Scientists in China have made a molecular spring that mimics stretchable systems in living systems, for example titin (a protein found in cardiac and skeletal muscles). 

Although molecular springs based on rotaxane are known, they can only change their length stepwise. This new rotaxane-based spring changes its length continuously as solvent polarity varies and so is a better mimic of biological springs.

Link to journal article
A solvent-driven molecular spring
Z Zhang et al
Chem. Sci., 2012, DOI: 10.1039/c2sc20728a

A new metal-organic framework (MOF) with the highest hydrogen uptake at 298K of all the MOFs that have been examined to date has been made by US scientists. The MOF exhibits exceptionally high hydrogen (58mg/g^-1 and 39g/L^-1 at 52 bar and 77K) and methane (276mg/g^-1 and 189g/L^-1 at 80 bar and 298K) uptake capacities, they say.

The team attributes the exceptionally high gas uptake capacity to the highly branched, aromatic-rich nature of the bridging ligand, optimal pore size and the open metal sites in the trizinc secondary building units.

The work highlights the potential of designing MOFs with even higher gas uptake capacities by further optimising their structural, chemical and topological characteristics. 

Link to journal article
A High Connectivity Metal-Organic Framework with Exceptional Hydrogen and Methane Uptake Capacities
D Liu et al
Chem. Sci., 2012, DOI: 10.1039/c2sc20601c

The first example of using an isolable carbene to dissociate homonuclear bonds (e.g. S-S, Br-Br) has been reported by researchers in the US.

The conditions are mild and metal-free – a surprisingly straightforward way to activate a variety of substrates. The dissociation of homonuclear bonds is critical to chemical reactions that range from the rearrangement of disulfide linkages in proteins to the synthesis of small molecules.

Link to journal article
Homonuclear Bond Activation Using A Stable N,N’-Diamidocarbene
K M Wiggins et al
Chem. Sci., 2012, DOI: 10.1039/c2sc20639k

Metallation is an entry point to constructing compounds, and by converting inert C-H bonds to reactive C-metal bonds, it opens up bond forming opportunities. Mixed metal reagents are widely used; combining an alkali metal with a softer, less reactive metal charges the softer metal component with super-reactivity, which, combined with good selectivity and functional group tolerances, makes the reagents superior to organolithium reagents. But how do they work? 

To remove the mystery surrounding these mixed-metal reagents, scientists in the UK have studied one such reagent in detail. They discover (surprisingly) that LiCd(TMP)₃ is unlikely to be an ate as previously thought, instead consisting of two independent homometallic amides. Rather than a synergistic metallation of the substrate, the metallation is a two step process: ortholithiation followed by transmetallation to cadmium.

Link to journal article
Opening the black box of mixed-metal TMP metallating reagents: direct cadmation or lithium-cadmium transmetallation
D R Armstrong et al
Chem. Sci. , 2012, DOI: 10.1039/c2sc20392h