Fe/PN(H)P Complexes

The P-stereogenic PN(H)P pincer ligands (R(Me)PCH₂CH₂)₂NH (R = Cy, ^tBu or Ph) and their iron(II) derivatives [FeBr₂(CO)(PN(H)P)] and [FeBrH(CO)(PN(H)P)] were developed by DFT-driven ligand design and tested in the asymmetric hydrogenation of ketones. A DFT study suggested that the Ph(Me)P-derived pincer should give high enantioselectivity, but in practice, 44% ee was achieved for acetophenone. The origin of this discrepancy was identified to be the incorrect assessment of CH/π interactions by DFT. Increasing the level of theory to post-Hartree-fock MP2 gives excellent agreement with experiment and is thus recommended for calculations in asymmetric catalysis where CH/π interactions are at the origin of enantioselectivity.