Dalton Transactions Blog

The catalytic potential of metal nanoparticles is widely understood and some are already used for heterogeneous catalysis.  In a dedication to Professor Cole-Hamilton, Karine Philippot and Bruno Chaudret et al. report the synthesis and characterisation of uniquely stabilised RuPt nanoparticles.

A diphenylphospine was used to stabilise bimetallic RuPt nanoparticles, both decorating them and affecting their chemical composition.  Neither an ordered alloy nor a core-shell structure was produced; instead, as proven by scattering and spectroscopic techniques, very disordered nanoparticles with Ru cores and alloy shells were observed. The mechanism that produces such an “onion” structure is thought to involve the reaction of the diphosphine ligands with Ru at the beginning of the reaction.

The use of reactive ligands in the synthesis of bimetallic nanoparticles can modify their structure, suggesting the possibility of finely tailoring the structure and surface of such nanoparticles in the future.  These modifications have already shown promise, with CO poisoning of RuPt nanoparticles having much less of an effect on hydrogenation reactions than with analagous pure Ru examples.

To find out more about these new bimetallic nanoparticles, download this HOT article now.

On the influence of diphosphine ligands on the chemical order in small RuPt nanoparticles: combined structural and surface reactivity studies
Patricia Lara, Tuğçe Ayvalı, Marie-José Casanove, Pierre Lecante, Alvaro Mayoral, Pier-Francesco Fazzini, Karine Philippot and Bruno Chaudret

Ever since Ziegler and Natta’s 1950s discovery of TiCl₄ as a catalytic precursor for alkene polymerization, interest in similar compounds with potentially superior properties has soared.

Biodegradable polylactic acid cups

Polylactide, polyglycolide and polycaprolactone are all commercially available biodegradable polyesters with advantages over non-biodegradable alternatives. They are used primarily in biomedical applications ranging from sutures, screws and pins to drug delivery and dentistry. Biodegradable polymers have also found uses in areas as diverse as compostable food packaging, plastics repair and rapid prototyping.

Marchetti et al. have reported a number of group 4 N,N-dialkylcarbamato complexes alongside their catalytic properties with regard to the ring opening polymerization of rac-lactide. They have also studied their polymerization mechanisms in great detail, concluding that the first stage of the polymerization reaction proceeds through different pathways for the Ti, Zr and Hf analogues, explaining the observed differences in activity. All pathways produce a vacant metal site, which is required for further propagation.

Read more about these new group 4 tetracarbamates and their application as catalytic precursors for the polymerization of rac-lactide in this HOT article.

Ring opening polymerization of rac-lactide by group 4 tetracarbamato complexes: activation, propagation and role of the metal
Fabio Marchetti, Guido Pampaloni, Calogero Pinzino, Filippo Renili, Timo Repo and Sirpa Vuorinen

Research in metal-organic frameworks (MOFs) or porous coordination polymers (PCPs) has exploded lately due to their potential applications in diverse areas from gas storage to drug delivery, but the Kitagawa group has been looking at yet another application that has rarely been considered: proton conductivity.  This process would work in a similar way to Nafion, a DuPont product produced since the 1960s in which protons on SO₃H groups hop between acid sites that extend from a Teflon backbone.  Modified Nafion’s excellent mechanical and thermal stability allow it to be used as a proton conductor for proton exchange membrane (PEM) fuel cells.

Foo et al. have synthesised a framework containing sulphonic acid groups, where sodium cations were exchanged in situ for protons.  The resultant framework proved to be unstable to loss of guest molecules and, as such, its use in most future applications is limited.

However, through a solid solution approach, where a mixture of ligands was used in differing proportions, mixed MOFs were produced.  The stand-out product was a framework in which 18% of the linkers contained sulphonic acid groups, which retained crystallinity and porosity following evacuation of guest molecules.  The incorporation of this small proportion of acidic groups increased both the total uptake and the heat of adsorption of CO₂ at 288 K.

Read about a solid solution approach as an alternative route to stabilising MOFs in this HOT article.

Almost ten years ago, Piers et al. described how frustrated aminoboranes could be used to activate molecular hydrogen by exploiting their frustrated Lewis pairs.  Unfortunately the ansa-aminoborane they investigated proved incapable of activating H₂, and so this contribution was very much overlooked in the ongoing search for facile H₂ activation.

A frustrated Lewis pair, in this case, is a molecule that contains a Lewis acid group and a Lewis base group kept apart due to sterics.  Such compounds are, perhaps unsurprisingly, very reactive.  The most important practical application of FLPs is most likely to be the catalysed hydrogenation of polar double bonds under ambient conditions.

The Repo group at the University of Helsinki describe how they have overcome the problems encountered in 2003 to produce two new ansa-aminoboranes which are both capable of activating molecular hydrogen under ambient conditions.  One of their new compounds even shows selective reversible H₂ activation at room temperature, providing exciting new developments for FLP catalysis.

Read more about these new catalysts, including why they outperform their predecessors, in this HOT article.

Hydrogen activation by 2-boryl-N,N-dialkylanilines: a revision of Piers’ ansa-aminoborane
Konstantin Chernichenko, Martin Nieger, Markku Leskelä and Timo Repo