Secondary phosphine oxides (SPOs) are an attractive alternative to classic tertiary phosphorus ligands in catalysis because of their special properties and stability (Scheme 1a). Their corresponding metal complexes exhibit a particular ability to cleave H2 heterolytically through the metal and the oxygen atom (Scheme 1b). Then, the complex can transfer the hydrogen atoms to a polarized substrate. In that regard, our group has a longstanding experience in the use of SPOs as multifunctional ligands, both in organometallic and metallic nanoparticle catalysis. We have used a specific SPO (tert-butyl(phenyl)phosphine oxide) for the synthesis of two iridium catalysts, an Ir–SPO complex and iridium nanoparticles (IrNPs) ligated with SPO ligands, which were compared mutually with the aim to establish the differences in their catalytic properties (Scheme 2). The Ir–SPO based catalysts exhibit totally different activities and selectivities in the hydrogenation of various substituted aldehydes. The Ir–SPO complex showed a very high activity and selectivity, whereas the IrNPs were less active, but proved to be more robust catalysts than the complex, giving high selectivities in the hydrogenation of substrates which poison the homogeneous catalyst. This study illustrates perfectly how the same metal and the same ligand can be used for the preparation of different catalysts with amazingly different properties.

Iridium versus iridium: Nanoparticle and molecular catalysts carrying the same ligand behave differently

255th National Meeting (2018)

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