The skies are leaden and we’re set for several days of rain. But the weather isn’t going to deter the thousands of chemists who’ve congregated here in Boston for this fall’s national ACS meeting. The technical program is particularly good this time round, so I’ve had some difficulty cherry-picking which seminars to attend.

I decided to kick off first thing on Sunday morning with an organic symposium held in memory of Keith Fagnou, who tragically died last year. Although the mood was inevitably somewhat sombre, the overall feeling was of a celebration of the chemistry that Keith loved. Indeed, much of the research discussed during the symposium had been influence by Keith’s work.

One theme that emerged was fluorination chemistry, an area that has seen some exciting developments recently – perhaps most notably with Steve Buchwald’s terrific paper in Science (see the abstract here) describing a catalytic cross-coupling process for attaching trifluoromethyl groups to aromatics. But Buchwald’s group is far from the only one developing this kind of reaction. John Hartwig described his work on the use of copper phenanthroline complexes for trifluoromethylation reactions. Although his reactions are currently stoichiometric, he pointed out that both the metal and the ligands are dirt cheap. The complexes can now be generated in situ in reactions, so I’ll watch with interest to see whether a catalytic version is forthcoming.

Melanie Sanford followed this up with two takes on the trifluoromethylation problem. Her first approach involves attaching perfluorinated alkyl radicals to aromatics. Although this works well for perfluorohexyl groups, currently it’s not so good for trifluoromethyl groups – but she’s confident that they’ll be able to optimize the trifluoromethylation reactions. Her second strategy is to use trifluoromethyl cations in cross-coupling reactions. The chief hurdle here is generating a catalytic cycle that has a high turnover number. Her group has now identified a catalytically competent, monomeric palladium(IV) compound for these reactions, a breakthrough that she hopes will overcome the turnover problem.

There’s lots more great chemistry on offer this week, so finding time to blog is difficult – but watch this space!

Andy

Andrew Mitchinson (Senior Editor, Nature)

There were many great talks yesterday at the Belgian Organic Synthesis Symposium, but as I have time to describe just one, I’ll mention Eric Jacobsen’s tour de force about hydrogen-bonding catalysis. This seems to be an area that’s really kicking off right now.

His thesis is that hydrogen-bonding catalysts shouldn’t be thought of in the way that chemists tend to conceptualize asymmetric catalysts in general – that is, as molecules or complexes that bind to substrates in order to block the approach of reactants from certain directions. Instead, he made the case that hydrogen-bonding catalysts act more like enzymes, activating and/or stabilizing the substrate (or the substrate’s transition state)through hydrogen bonding. That’s not to say that steric interactions are unimportant, clearly they still have an impact. But to fully understand how hydrogen-bonding catalysts work, he argues that you need to look first at the stabilizing effects of non-covalent interactions.

He backed this up with many case studies of hydrogen-bonding catalysts from his own lab (such as those for Claisen rearrangements, polyene cyclizations and Strecker-like reactions), in each case providing a detailed analysis of how each catalyst works. It’s all beautiful stuff, and you find some it in JACS (see the abstract for his analysis of the Strecker reaction here).

Today is the last day of the meeting, so this is where I’ll sign off from Belgium. I’ve only been able to discuss a handful of the presentations, but there were many other highlights at this meeting. I can only encourage organic chemists out there to come to the next meeting in the BOSS series, in 2012 – you won’t be disappointed.

Andy

Andrew Mitchinson (Senior Editor, Nature)

Day three of the Belgian Organic Synthesis Symposium, and the heat wave continues. That means there have been plenty of excuses for conference attendees to drink Belgian beer, as the title of this blog implies. But we were also treated to a spectacular talk today by Kenichiro Itami, who presented (among other things) his latest research towards the bottom-up synthesis of carbon nanotubes.

Itami’s grand strategy is to prepare nanorings of benzenes, known as cycloparaphenylenes (CPPs), then to stack them up into cylinders and join them together in aromatization reactions – hey presto, you get a carbon nanotube. He’s not the only person pursuing this strategy, as both Carolyn Bertozzi and Shigeru Yamago seem to be trying the same thing.

The first problem to overcome in this approach was how to make the inherently ring-strained CPPs – Bertozzi published her solution in 2008 (you can see the abstract for the JACS paper here), closely followed by Itami in 2009 (in Angewandte, abstract here), then by Yamago this year (also in Angewandte, abstract here). Itami is now concentrating on finding a scaleable route for making CPPs, so that he has sufficient material to attempt the all-important aromatization reaction. He’s not quite there yet, but he has come up with an impressively concise synthesis of a CPP, and just needs to optimize the yields.

In the mean time, he’s also devised a general, modular synthesis that allows access to CPPs of different sizes, and he presented some rather beautiful crystal structures of a CPP – interestingly, the molecules stack up in much the way you would need them to if you wanted to fuse them together into a nanotube.

No doubt Bertozzi and Yamago are also making advances of their own, so I’ll certainly be following the progress in the race for a bottom-up synthesis of carbon nanotubes.

Andy

Andrew Mitchinson (Senior Editor, Nature)

I enjoyed the Belgian Organic Synthesis Symposium in 2008 so much that I decided to go to another one. So, here I am in Namur, capital of the Wallonian region of Belgium, where they’ve been having a mini-heatwave – and where my hotel room has no air conditioning. So, forgive me if this turns out to be a short entry, but it’s hard to concentrate on blogging when the temperature is 30 °C.

The meeting has got off to a terrific start, with Dave MacMillan undergoing the usual rite of passage as the recipient of the ‘Tetrahedron Chair’ prize – he gave four lectures today on organocatalysis. The lectures are billed as a one-day course, and so unsurprisingly there wasn’t much in the way of new results. But there were a few teasers of things to come from the MacMillan lab. Look out for Dave’s forthcoming synthesis of strychnine, completed in an amazing 12 steps. I think this might be the shortest route ever, but feel free to correct me. Dave also mentioned that his lab is currently looking for alternatives to Hantzsch esters as hydride sources for organocatalytic reductions, and briefly described a soon-to-be-published method for the alpha-amination of aldehydes.

You might think that a whole day listening to one person speak would be wearing, but Dave has such a conversational style that his lectures feel more like one-to-one chats, in which he gives you the inside scoop on how his greatest discoveries were made. Even the lure of free Belgian beer (given away as a freebie at the end of today’s programme) didn’t deprive him of any of his audience.

And speaking of Belgian beer, the thought of a cold, frosty one is extremely appealing from my oven of a hotel room. So I’m going to go and get one.

Andy

(Andrew Mitchinson, Senior Editor, Nature)

I’m not sure why, but the polymer sessions at ACS meetings always seem to be in venues away from the main conference centre. What do polymer chemists make of this, I wonder? Do they feel that they’re being hived off for some reason? Or do they actually quite like having a venue more or less to themselves? If there are any polymer people out there that would like to comment on this, I’d love to know.

A sense of direction was never my strongest point, and so it was that I got lost on the way to the hotel where the polymer talks were being held (which was embarrassing, because the hotel is just around the corner from the Washington Conference Center). Arriving with seconds to spare, I found that someone had seriously miscalculated the size of the room needed for the afternoon session. As the chairperson, Craig Hawker, commented, “This is the smallest lecture room Bob Grubbs will ever lecture in.” People were spilling out into the corridor, the air-con couldn’t cope, and frankly I wasn’t sure I’d be able to stick it out for long.

Fortunately, a swap was arranged with another session, providing us with a room three times the size of the original one, which we instantly filled. More chairs were brought in, but by the end of the afternoon it was still standing room only.

So why all the interest? Because it was a stellar line-up. Not just the aforementioned Bob Grubbs, but also Krysztof Matyjaszewski, Dave Bergbreiter and Karen Wooley, to name but a few. There was too much good stuff to cover here, but I liked Rachel O’Reilly’s work making metal-lined nanocages (Soft Matter subscribers can read about this here); Craig Hawker’s description of reactive polymers that have ketenes in their side-chains, which can be used for cross-linking or functionalization (the polymers can be used for microcontact printing applications); and Karen Wooley’s tour de force about nanoparticles that carry DNA plasmids into cells (Biomaterials subscribers can see some of this work here). Karen is currently using nanostructures as building blocks for complex molecular assemblies, for example by decorating anionic nanocylinders with cationic nanospheres; the anionic cylinders won’t enter cells, but they can do when coated with the cationic spheres. She’s ultimately hoping that her nanostructures will be useful for therapies targeting lung injuries.

I have to say that this was my favourite session of the meeting so far – the science was great, but there was also a genuine sense of camaraderie among the people in the room, with lots of interest in each talk demonstrated by the number of questions asked. Which made up for the fact that I got lost again on the way back to my hotel…

Andy

Andrew Mitchinson (Senior Editor, Nature)

There’s so much good stuff going on at the ACS meeting that it’s tough finding time to blog, so here I am catching up on yesterday’s talks. Let’s kick off by talking about a brilliant session on inorganic nanochemistry. Zhong Lin Wang described his work with piezoelectric ZnO nanowires, especially looking at how they can be used to make nanogenerators for powering devices. One of the latest developments is a widget that produces an oscillating current as it flexes, effectively acting as an AC generator – Nature Nanotechnology subscribers can read a paper about this here. Zhong Lin wowed the audience by showing how such devices could be built into a jacket for a hamster; when the hamster went for a run in its wheel, the animal’s movement generated electricity! (Nano Letters subscribers can see this here.)

Equally impressive was Yi Cui’s talk about the use of nanostructured surfaces for making efficient photovoltaic devices. By making solar cells lined with nanocones or nanodomes of silicon, the energy density of the cells reaches 17.5 mA per square centimetre – which according to Yi is “world-beating”. The silicon nanocones are better at trapping light than films of amorphous silicon, absorb light across a range of wavelengths (Yi showed data spanning 400 to 800 nanometres), and also efficiently absorb light that strikes the cell obliquely. I was particularly struck by pictures that compared amorphous silicon with the nanostructured stuff – amorphous silicon is grey, whereas the nanocone material is totally black, thus providing a simple demonstration of light absorption properties that even I could understand!

There was lots of other cool stuff (including a tantalizing mention from Yi about nanoribbon topological insulators that should solve a fundamental problem in spintronics, manuscript currently in press), but now I really want to say something about polymers (see my next blog entry)…

Andy

Andrew Mitchinson (Senior Editor, Nature)

Have you ever wondered how you would evacuate several thousand people from a hangar-sized conference centre in the event of a fire? Well, now I know, because all the fire alarms went off yesterday morning at the Washington Conference Center. I’m pleased to report that there was no mad panic (chemists, of all people, know how to respond to fire-related emergencies) but it has to be said that it does take a long time – the all-clear had been sounded before I made it to the exit. It turned out to be a false alarm, by the way.

I felt sorry for the poor speakers who were interrupted mid-flow by sirens and flashing lights, but an honourable mention must go to the presenter at the session that I was attending: Malika Jeffries-EL handled the interruption with magnificent aplomb. And everybody came back to see the rest of her talk – about the synthesis of benzobisazoles as building blocks for conjugated polymers – once the alarm was over.

Later in the same session, Tehshik Yoon spoke about his work on visible-light-driven photochemical reactions, specifically [2+2] cycloadditions. The key to using visible light for these reactions is the ruthenium catalyst; JACS subscribers can read about some of this work here, in a paper that describes intermolecular cycloadditions. Yoon has now tweaked the chemistry so that it works in crossed intermolecular reactions, and that work is currently in press.

I wonder if visible-light-driven reactions might become something of a theme for the future, as David MacMillan is, of course, also working in this field. He spoke about the development of his photoreactions for the asymmetric alkylation of aldehydes (Science subscribers can read the first paper on this topic here). The latest development in this story will undoubtedly be of interest to medicinal chemists: a method for the trifluoromethylation of aldehydes, which is currently in press.

News from today’s sessions later…

Andy

Andrew Mitchinson (Senior Editor, Nature)