New tetradentate ligand exposes metal

Chemists have synthesized the first tetradentate ligand containing three phosphaalkenes, which, in complexes with rhodium and iridium, forms binding pockets that could lead to new chemistry at the metal site (Organometallics 2016, DOI: 10.1021/acs.organomet.6b00250). A team led by chemistry professor Matthew F. Cain of the University of Hawaii, Manoa, synthesized the tris(phosphaalkene)phosphine ligand in a single step from an ortho-substituted triphenylphosphine scaffold. Each phosphaalkene group contains a bulky substituent, 2,4,6-tri-tert-butylbenzene. When complexed with Rh or Ir, the ligand closes around the metal to form a cup-shaped structure. The combination of a pocket that harbors an exposed metal site and low-lying π* orbitals creates an unusual steric and electronic environment, which could allow chemistry with typically unreactive species, the authors say.