Complexes of Ni(II) with triphosphine‐phosphite ligand P(OCH₂PPh₂)₃: syntheses, structures, and electronic properties

Abstract

Ionic complexes [(κ4−PP3)P(OCH2PPh2)3NiX]BF4 (2 (X=Cl) and 3 (X=Br)) were formed when P(OCH2PPh2)3 ligand (1) was reacted with mixtures of salts NiX2/Ni(BF4)2 (X=Cl or Br). Single crystal X‐ray characterizations performed on complexes 2 and 3 established that metal centers are in pseudo‐trigonal bipyramidal ligand geometries formed by the phosphorus centers from coordinated 1 and the halide ligand. Reactions of 1 with other nickel(II) salts (acetate, nitrate or tetrafluoroborate) proceeded in 2 : 1 (ligand‐salt) ratio yielding complex 4, [(κ3−PP2)((−O−P)(OCH2PPh2)2)(κ2−PP)(−O−P)(OCH2PPh2)(OCH2P(=O)Ph2)Ni]. The formation of this complex required hydrolysis of one of the P−O ester bonds in ligand P(OCH2PPh2)3 thus forming O‐anionic phosphite/diphosphine fragment [−O−P(OCH2PPh2)2]. One of such fragments is coordinated to the metal center as a tridentate (κ3−PP2) ligand, whereas the other is in bidentate (κ2−PP) coordination via phosphorus centers of the −O‐P‐OCH2PPh2 chelating pocket; the remaining ‐OCH2P(=O)Ph2 arm is P‐oxidized and uncoordinated. Nickel center in 4 is in distorted trigonal‐bipyramidal geometry, with O‐anionic‐phosphite groups coordinated at the axial positions, and the three ‐PPh2 groups located in the equatorial plane. Compounds 2–4 were characterized by multinuclear NMR spectroscopy, elemental analyses, electron absorption spectroscopy, cyclic voltammetry, and single crystal X‐ray crystallography. Their electronic structures were also investigated by DFT methods.