Hydroboration of Alkynes Catalyzed by Fe(II) PCP Pincer Complexes

The hydroboration reaction is in all cases highly <i>syn</i>-selective. The reaction requires no additives and proceeds with a catalyst loading of 1–2 mol % at 45–55 °C. An active pre-catalyst is the bench-stable alkyl Fe(II) complex [Fe(PCP^CH2-<i>i</i>Pr)(CH₂CH₂CH₃)(CO)₂].

This complex reacts with an excess of HBpin to form the Fe(II) pinacolborane complex [Fe(PCP^CH2-<i>i</i>Pr)(κ²-H₂BPin)(CO)], which is an equally active pre-catalyst but more difficult to handle, as it decomposes in the absence of substrates. Both pre-catalysts afford the highly reactive hydride catalyst [Fe(PCP^CH2-<i>i</i>Pr)(H)(CO)] under catalytic conditions. A broad variety of aromatic and aliphatic alkynes were efficiently and selectively borylated.