Mysterious palladium clusters

Earlier this week, and while still in Shanghai, I heard a thought-provoking talk by Professor Max Malacria of the Université Pierre et Marie Curie. This research, recently published by Angewandte Chemie, is built around a serendipitous finding made when isothiourea was reacted with one equivalent of [Pd(dba)2] and an equimolar amount of tris(p-fluorophenyl)phosphine in dichloromethane at room temperature. The red crystalline product formed during this transformation is a fascinating cluster shown below (characterized by X-ray crystallography). This begs a question: how is it that this was never seen before, with all those palladium chemists putting every structural aspect under scrutiny? I suppose this goes to show how little we know about what goes on in our flasks. By the way, Max mentioned another, even simpler, means of preparing this compound (I cannot disclose this) which makes me really wonder why this sort of chemistry had remained veiled until recently. Curiously, the overall composition of the cluster contains what one would instinctively fear in palladium catalysis: the dreaded association with the thiolate “poison”. But the cluster, which combines three palladium atoms, three phosphines, and three thiolate ligands, is apparently catalytically active and is quite stable. I am certain there will be a lot more applications of this chemistry in the future. They say that necessity is the mother of invention, but I think it is more about serendipity.

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http://onlinelibrary.wiley.com/doi/10.1002/anie.201310204/abstract

2 thoughts on “Mysterious palladium clusters

  1. The claim in this Angew Chem paper that cyclic ti-palladium clusters are “new and unprecedented aromatic species” is plain false.

    Stephanie Hurst from miniature Department of Chemistry and Biochemistry, Northern Arizona University, Flagstaff, Arizona, has been quietly making them for almost a decade. Her tripalladium and triplatinum clusters are sandwiched between two tropylium rings, like giant trinuclear ferrocene

  2. Indeed. But what is interesting, though, is that Pd atoms in the Hurst case are completely shielded… I will be surprised if her complexes survive any catalysis. But thanks for bringing this to my attention!

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