Synthesis of Nickel(II) Complexes Containing Oxadithioether Ligands and Their Catalytic Properties in Propylene Oligomerization
摘要
Nickel complexes with oxadithioether ligands [Ni(L)Br2] and [Ni(acac)(L)]CF3SO3 (L = R(S(CH2)2O(CH2)2S)R, R = Me, Et, n-Pr, i-Pr, n-Bu, i-Bu, benzyl, n-hexyl) were synthesized. The structural features of these complexes were analyzed by NMR and FTIR, elemental analysis as well as electrospray ionization mass spectrometry and density functional theory calculations. It was found that the signals in the 1H NMR spectra are broadened and shifted due to paramagnetic properties caused by the presence of the Ni(II) ion. The crystal structure of [Ni(Et(S(CH2)2O(CH2)2S)Et)(MeCN)Br2] (I) was determined by X-ray diffraction. In I, the coordination sphere of nickel is characterized by a slight distortion of the octahedral geometry of the central atom, and the oxadithioether ligand is coordinated tridentately in a meridional configuration. It was found that the catalytic systems {[Ni(L)Br2] or [Ni(acac)(L)]CF3SO3}/Al(i-Bu)2Cl in the presence of H2O additives as a promoter are characterized by high catalytic activity in propylene oligomerization. Using the [Ni(L)Br2]/Al(i-Bu)2Cl (L = R(S(CH2)2O(CH2)2S)R, R = n-Bu) catalyst system TON = 365900 mol C3H6/mol Ni (T = 25°C, solvent — 1,2-dichloroethane) with TOF = 4840 min−1 and dimers selectivity of 78% was obtained. Hypotheses of the routes of interaction of the [Ni(L)Br2] and [Ni(acac)(L)]CF3SO3 complexes with organoaluminum compounds in the presence of water additives, leading to catalytically active species, are discussed.