The aim of this review is to highlight how the diversity generated by N-substitution in the well-known short-bite ligand bis(diphenylphosphino)amine (DPPA) allows a fine-tuning of the ligand properties and offers a considerable scope for tailoring the properties and applications of their corresponding metal complexes. The various N-substituents include nitrogen-, oxygen-, phosphorus-, sulfur-, halogen-, and silicon-based functionalities and directly N-bound metals. Multiple DPPA-type ligands linked through an organic spacer and N-functionalized DRPA-type ligands, in which the PPh2 substituents are replaced by PR2 (R = alkyl, benzyl) groups, are also discussed. Owing to the considerable diversity of N-functionalized DPPA-type ligands available, the applications of their mono- and polynuclear metal complexes are very diverse and range from homogeneous catalysis with well-defined or in situ generated (pre)catalysts to heterogeneous catalysis and materials science. In particular, sustained interest for DPPA-type ligands has been motivated, at least in part, by their ability to promote selective ethylene tri- or tetramerization in combination with chromium. Ligands and metal complexes where the N-substituent is a pure hydrocarbon group (as opposed to N-functionalization) are outside the scope of this review. However, when possible, a comparison between the catalytic performances of N-functionalized systems with those of their N-substituted analogs will be provided.

The coordination chemistry of the DPPA-type functional phosphine bis(diphenylphosphino)(N-thioether)amine N(PPh2)2(CH2)3SMe () and its monosulfide derivative, (Ph2P)N{P(S)Ph2}(CH2)3SMe (1·S), towards Ni(II) precursors has been investigated. The crystal structures of N{P(S)Ph2}2(CH2)3SMe (1·S2), [NiCl2{(Ph2P)2N(CH2)3SMe-P,P}] (2), [NiCl2((Ph2P)N{P(S)Ph2}(CH2)3SMe-P,S)] (3), [Ni((Ph2P)N{P(S)Ph2}(CH2)3SMe-P,S)2]NiCl4 (3'), [Ni((Ph2P)N{P(S)Ph2}(CH2)3SMe-P,S)2](BF4)2 (4), and [Ni((Ph2P)NH{P(S)Ph2}-P,S)2]Cl2 (5) have been determined by single-crystal X-ray diffraction. In all of the complexes with the hybrid ligand 1·S, P,S-chelation to the Ni(II) center is observed. Despite the stability generally associated with five-membered ring chelation, easy migration of this LL'-type P,S-chelating ligand from one metal center to another was observed, which accounts for the reversible ligand-redistribution reaction occurring in the equilibrium between the neutral, diamagnetic complex [NiCl2LL'] and the paramagnetic ion-pair [Ni(LL')2][NiCl4]. Detailed investigations by multinuclear NMR, UV/Vis, and FTIR spectroscopic methods and DFT calculations are reported. Each of the formula isomers 3 and 3' can be selectively obtained, depending on the experimental conditions.