β-Diketiminato 3d-metal compounds: Synthesis, characterization and catalytic behavior towards ethylene

The lithium β-diketiminate (1c, [Li{N(2,6-iPr2C6H3)C(Ph)CHC(tBu)NH}]2 represented as (LiL)2) reacted with 3d-metal (II) chlorides to afford the corresponding compounds (2–7). All metal compounds were fully characterized by elemental, spectroscopic analyses and the single-crystal X-ray diffraction. The coordination geometries around the metals are shown to be tetrahedral within the trinuclear Co2Li compound (2), planar in ML2 (M = Co, 3), pseudo-tetrahedral conformation in the ML2 with M as Mn (4), Fe (5) or Zn (6), and square planar in the dinickel compound (7). Indicated by the trimetallic Co2Li compound 2, a six-membered ring is constructed of three metal atoms and three bridged chlorides as a twisted conformation. An inversion center is present in the centroid of the Ni2Cl2 four-membered ring within compound 7. The plausible mechanism of forming ML2 was proposed through the chloro-bridged multinuclear compounds on the basis of isolated intermediates of trinuclear (2) and dinuclearic (7) compounds. Upon treatment with methylaluminoxane (MAO), the nickel compound 7 possessed good activity towards ethylene oligomerization, whereas the other metal compounds showed moderate activities towards ethylene polymerization.

Graphical abstractThe lithium β-diketiminate [Li{N(2,6-iPr2C6H3)C(Ph)CHC(tBu)NH}]2 reacts with late 3d transition metal (II) chlorides to afford mononuclear, dinuclear and trinuclear compounds. All metal complexes were fully characterized by elemental and spectra analyses along with the single-crystal X-ray diffraction. The variety of their molecular structures showed the plausible stepwise pathway in forming the metal complexes through chloride-bridged multi-nuclear complexes. Their catalytic behaviors in ethylene reactivity were also investigated.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► The lithium β-diketiminate reacted with 3d-metal (II) chlorides to form mononuclear, dinuclear and trinuclear metal complexes. ► A trinuclear complex was directly transformed into a mononuclear complex. ► All metal complexes were fully characterized by elemental and spectra analyses along with the single-crystal X-ray diffraction. ► The plausible pathway in forming metal complexes is proposed. ► Their catalytic behaviors in ethylene reactivity were also investigated.