Protons and Hydride in Gold Catalysis

At that point, we had a closer look at the possibility of P-H eliminations at gold(I) alkyl compounds [51]. We chose the IPr NHC ligand, as this was the ligand that allowed the isolation [52] of the first stable gold(I) hydrides. 

As the most important finding of the computational study, it was revealed that there is a pathway for the fi-H elimination, but the overall barrier is so high that this reaction should proceed only at temperatures of about 220 C, which means that this step indeed should be irrelevant for all homogeneous gold-catalyzed reactions published so far. 

The subsequent experimental verification of these results indeed proved that IPrAu-alkyl compounds start to decompose only at temperature of about 180 °C. In analogy with organomercury compounds, this decomposition could be based on a homolytic metal-carbon bond cleavage. 

At the stage of vinylgold or arylgold intermediates, most catalytic cycles show the proto-deauration as the final step. In many of these reactions, rather than a direct proton transfer from the nucleophile which was added, a long-distance proton transfer is necessary. A detailed investigation revealed that gold catalysis not only tolerates water but also utilizes clusters of four or more water molecules as proton shuttles [53]. 

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