Thursday, April 3, 2014

Gold Steps Up

Update, 4/5/14: On Twitter, Yunus chimes in to recommend this Hashmi paper, showing a mononuclear Au(I) catalyst - with crazy adamantyl appendages - that gets down to 0.0001% loading!

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Catalyst: A substance that increases the rate of a reaction without modifying the overall standard Gibbs energy change in the reaction (IUPAC Gold Book).

Though most chemists agree on the above definition, there have always been two camps: "Academic" catalysis (1-20 mol%, 5-100 turnovers), and "Industrial" Catalysis (<0.01 mol%, >10,000 turnovers). As more researchers seek to translate early discoveries into efficient, "green" processes, the desire for robust organometallic species has skyrocketed.

Right now, a few such homogeneous catalysts have made the jump: the Grela Ru metathesis catalysts (0.001%), copper catalysts for boron addition (0.005%), and some iridium and palladium species.

Gerald Hammond and Bo Xu (Louisville) want to add one more to the list: a highly-stable gold catalyst. Their new catalyst, dubbed "BisPhePhosXD-AuCl" (Phew!), takes development lessons from Buchwald (electron-rich, C-to-metal bond) and Widenhoefer (steric bulk to discourage off-cycle species). 

Now here's the fun part: the authors run several typical gold-catalyzed reactions side-by-side with their improved catalyst. In most cases, they're able to shave off 99.9% of the catalyst loading, with comparable yields. Granted, certain reactions take more time with this approach, but a few finish ahead of their literature counterparts. Wow.

Aldrich sells the precatalyst, if you're itching to try it yourself. I'll be very interested to see the next generation of bulked-up ligands, and whether this reactivity transfers over to other precious metals, namely platinum, iridium, or rhodium.

3 comments:

  1. a word of caution: reactions that run with very low catalyst loadings either have to employ a robust catalyst, or they use highly optimized procedure and carefully purified starting materials. This kind of development work is better suited to process chemists. Especially if you have to form the catalyst in situ from a ligand and a metal source, with air sensitive precursors, it is a lot easier to perform it on large scale.

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  2. Lavallo and coworkers have an impressively active single component gold catalyst using a carborane.
    http://onlinelibrary.wiley.com/doi/10.1002/anie.201209107/abstract

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