text: The first transition metal complexes of nontrigonal pnictogen compounds have been reported in the 1980s and '90s. Up to now, several complexes have been successfully synthesized, but they have not yet been applied in secondary processes, such as catalytic cycles.
  In 2018, the synthesis and reactivity of a chelating ligand containing a nontrigonal phosphorus center was reported. It is worth noting that, apart from direct metalation of this ligand with RuCl(PPh), metalation with a ruthenium hydride compound RuHCl(CO)(PPh) yields a complex with net insertion into the Ru−H bond. These ligands, along with recent developments for higher valent states of Sb ligands, may possess rich potential in the field of catalysis and sensing.