Mono- and diylide-substituted phosphines (YPhos): Impact of the ligand properties on the catalytic activity in gold(i)-catalysed hydroaminations

Abstract

Understanding the impact of ligand properties on their performance in catalysis is seminal for future ligand design and catalyst improvement. In this work, the influence of the steric and electronic properties on the efficiency of a series of mono- and diylide-functionalized phosphines of type YCNPR2 and (YCN)2PR (with YCN = Ph3PC(CN) and R = Ph, Cy or tBu) on their efficiency in gold(i) catalyzed haydroaminations is studied. The diylidephosphines are particularly electron-rich and sterically encumbering but led to lower conversions than expected based on their donor strength. Systematic analysis of the relation between the donor strength and the catalytic activity revealed a linear correlation for the monoylide-functionalized phosphines. Thus, the most electron-rich phosphine YCNPtBu2 gives rise to the most active catalyst with turnover numbers greater than 5000. In contrast, no correlation was found for the diylide compounds due to steric congestions which overcompensated the beneficial electronic properties. Accordingly, higher temperatures had a stronger impact on the diylide phosphine-based catalysts, thus leading to similar activities of YCNPtBu2 and (YCN)2PCy at 50 °C. Overall, these results provide valuable information for future ligand design and the general impact of steric and electronic properties on the catalytic activity.