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

• Published in: Inorganica Chimica Acta 2011-05, Vol.370 (1), p.215-223
• Main Authors: Yuan, Shifang, Bai, Shengdi, Tong, Hongbo, Wei, Xuehong, Liu, Diansheng, Sun, Wen-Hua
• Format: Article
• Language: English
• Subjects: Ethylene oligomerization; Late transition metal; MAO; Molecular structure; β-Diketiminate
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/j.ica.2011.01.063

The lithium β-diketiminate [Li{N(2,6- i Pr 2C 6H 3)C(Ph)CHC( t Bu)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. [Display omitted] ► 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. The lithium β-diketiminate ( 1c, [Li{N(2,6- i Pr 2C 6H 3)C(Ph)CHC( t Bu)NH}] 2 represented as (Li L) 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 Co 2Li compound ( 2), planar in M L 2 (M = Co, 3), pseudo-tetrahedral conformation in the M L 2 with M as Mn ( 4), Fe ( 5) or Zn ( 6), and square planar in the dinickel compound ( 7). Indicated by the trimetallic Co 2Li 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 Ni 2Cl 2 four-membered ring within compound 7. The plausible mechanism of forming M L 2 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.