This article outlines two related bidentate organophosphorus ligand systems prepared by phosphorus-nitrogen (P-N) bond formation - R-2(E)PNHPR2, RC(E)NHPR2 (E = O, S, or Se) and their derivatives. The focus is on the extensive coordination chemistry exhibited by these systems to transition metals. A brief description of the syntheses of the ligands and metal complexes is given. (C) 1998 Elsevier Science S.A. All rights reserved.