Phosphine−Substrate Recognition through the C−H···O Hydrogen Bond: Application to the Asymmetric Pauson−Khand Reaction

A unique methine moiety attached to three heteroatoms (O, P, S) and contained in the PuPHOS
and CamPHOS ligands serves as a strong hydrogen-bond donor. Nonclassical hydrogen bonding of this
methine with an amido-carbonyl acceptor provides a completely diastereoselective ligand exchange process
between an alkyne dicobalthexacarbonyl complex and a phosphine ligand. This weak contact has been
studied by means of X-ray analysis, 1H NMR, and quantum mechanical calculations and revealed that the
present interaction falls in the range of strong C−H···OC bonds. The hydrogen-bond bias obtained in
the ligand exchange process has been exploited in the asymmetric intermolecular Pauson−Khand reaction
to yield the corresponding cyclization adducts in up to 94% ee.