Synthesis and structures of the transition metal(II) β-diketiminates [ML2] (M = Mn, Fe, Ni, Cu, Pd), [ML2′] (M = Ni, Cu) and [M(η3-C3H5)L] (M = Ni, Pd); L or L′ = [{N(SiMe3 or H)C(Ph)}2CH]

A series of crystalline late transition metal β-diketiminates 1–10, using the ligand [{N(SiMe3)C(Ph)}2CH]− (≡ L−) or [{N(H)C(Ph)}2CH]− (≡ L′−) is reported. The homoleptic pseudo-tetrahedral crystalline complexes [M(L)2] [M = Mn (1), Fe (2), Ni (3), Cu (5) were prepared from [Li(L)]2 and the appropriate anhydrous MCl2 in thf. The planar metal analogues [M(L′)2] [M = Ni (4), Cu (6)] were obtained for 4 from NiCl2 and [Li(L)]2 in thf followed by chromatography on hydrated alumina, or for 6 from hydrated CuSO4 and either [Li(L)]2 or H(L). The precursor for [Pd(L)2] (7) and [{Pd(L)(μ-Cl)}2] (8) was [Pd(cod)Cl2] (one or two molar equivalents), while the allyl complexes [Pd(η3-C3H5)(L)] (9) or [Ni(η3-C3H5)(L)] (10) were prepared from [{Pd(η3-C3H5)(μ-Cl)}2] or [{Ni(η3-C3H5)(μ-Br)}2], respectively. Whereas in each of the crystalline complexes 1–6 the MNCCCN rings are planar, in the centrosymmetric 7 and in 9 they are boat-shaped. The compounds 1, 2, 3, 5 and 6 (unlike 4, 7, 8 and 9) are paramagnetic; the magnetic moment in CDCl3 corresponds approximately to a low-spin complex for 1 and a high-spin complex for 2. The molecular structures of the crystalline compounds (X-ray data) 2, 3, 4, 5, 6, 7 and 9 are presented. Quantum chemical calculations (B3LYP) on the Ni(3) and Pd(7) complexes correlated well with the experimental structures, although the calculated Gibbs free energy for both tetrahedral and square-planar geometries showed the latter configuration more stable than the former by ca. 60 (Ni) and 100 (Pd) kJ mol−1 over a range of temperatures.

The X-ray analysis of the homoleptic metal(II) β-diketiminates showed three structural types: (i) pseudo-tetrahedral complexes with planar rings formed by the metal atom M and the κ2-N,N′-coordinated ligand (M = Mn, Fe, Ni, Cu), (ii) square-planar complexes with planar metal–ligand rings (M = Ni, Cu), and (iii) a square-planar complex with boat-shaped M–L rings (M = Pd).Figure optionsDownload as PowerPoint slide