Chelate complexes LM/n of transition metals with phosphinoimidic amidato ligands R2P(NR′)2- (= L)

Article abstract of DOI:10.1002/(sici)1521-3749(199805)624:5<837::aid-zaac837>3.0.co;2-f

Reaction of LLi with metal halides or metal halide complexes affords chelate complexes LM/n (L = R₂P(NR′)₂^-; M = Cr⁺⁺⁺, Co⁺⁺, Ni⁺⁺, Zn⁺⁺). With the bulky ligand t-Bu₂P(NSiMe₃)₂^- and Ni(PPh₃)₂Cl₂ or Ni(dme)Br₂ (dme = dimethoxyethane) only halide bridged chelates [LNiHal]₂ (Hal = Cl, Br) containing tetrahedral chromophors NiN₂Hal₂ were obtained. Main objects of investigation were the bischelates L₂Ni 2. 2a (R = i-Pr, R′ = Me) and 2c (R = Ph, R′ = Et) are planar, 2b (R = i-Pr, R′ = Et) and 2d-g (R, R′ = i-Pr, i-Pr; Ph, i-Pr; Et, SiMe₃; Ph, SiMe₃) tetrahedral. In solutions of 2b and 2c a conformational equilibrium planar (diamagnetic) ? tetrahedral (paramagnetic) exists that is shifted to the right with increasing temperature and is dominated by the tetrahedral (2b) or planar conformer (2c) at room temperature. As is the case with the isovalence electronic compounds [R₂P(S)NR′]₂Ni small substituents R′ apparently favour the planar state and in contrast to some complexes [R₂P(O)NR′]₂Ni no paramagnetic planar species 2 have yet been observed. These findings that are derived from the results of magnetic measurements and of UV/VIS as well as NMR spectroscopy are confirmed by crystal structure determinations: 2a was found to be planar (orthorhombic; a = 3382.8(11), b = 1124.0(4), c = 8874(3); P2₁2₁2; Z = 6), and 2g to be tetrahedral (monocline; a =1268.4(2), b = 1806.8(2), c =1971.6(2), P2₁/n; Z = 4). The bite angle NNiN of the chelate ligand in 2a (ca. 77°) is similar to those in paramagnetic planar complexes [R₂P(O)NR′]₂Ni (NNiO 74-77°) and shows that a small chelate bite does not necessarily imply paramagnetism of planar Ni(II) complexes. Johann Ambrosius Barth 1998.