What is "spanphos"

SPANphos is an organophosphorus compound used as a ligand in organometallic and coordination chemistry. This compound is a rare example of a trans-spanning ligand and rigidly links mutually trans coordination sites. By virtue of its chiral backbone that forms a chiral cavity over the face of a square planar complexes, e.g. in MCl(SPANphos) (M = Pd, Pt).