1038986-83-2Relevant articles and documents
Nickel and iron complexes with N,P,N-type ligands: Synthesis, structure and catalytic oligomerization of ethylene
Kermagoret, Anthony,Tomicki, Falk,Braunstein, Pierre
, p. 2945 - 2955 (2008/09/21)
The N,P,N-type ligands bis(2-picolyl)phenylphosphine (1), bis(4,5-dihydro-2-oxazolylmethyl)phenylphosphine (2), bis(4,4-dimethyl-2- oxazolylmethyl)phenylphosphine (3) and bis(2-picolyloxy)phenylphosphine (4) were used to synthesize the corresponding pentacoordinated Ni(ii) complexes [Ni{bis(2-picolyl)phenylphosphine}Cl2] (6), [Ni{bis(4,5-dihydro-2- oxazolylmethyl)phenylphosphine}Cl2] (7), [Ni{bis(4,4-dimethyl-2- oxazolylmethyl)phenylphosphine}Cl2] (8) and [Ni{bis(2-picolyloxy) phenylphosphine}Cl2] (9), respectively. The hexacoordinated iron complexes [Fe{bis(2-picolyl)phenylphosphine}2][Cl 3FeOFeCl3] (10), [Fe{bis(4,5-dihydro-2-oxazolylmethyl) phenylphosphine}2][Cl3FeOFeCl3] (11) and the tetracoordinated complex [Fe{bis(4,4-dimethyl-2-oxazolylmethyl)phenylphosphine} Cl2] (abbreviated [FeCl2(NPNMe2-N,N)]) were prepared by reaction of FeCl2?4H2O with ligands 1-3, respectively. The crystal structures of the octahedral complexes 10 and 11, determined by X-ray diffraction, showed that two tridentate ligands are facially coordinated to the metal centre with a cis-arrangement of the P atoms and the dianion (μ-oxo)bis[trichloroferrate(iii)] compensates the doubly positive charge of the complex. The cyclic voltammograms of 10 and 11 showed two reversible redox couples attributed to the reduction of the dianion (Fe 2OCl6)2- (-0.24 V for 10 and -0.20 V for 11vs. SCE) and to the oxidation of the Fe(ii) ion of the complex (0.67 V for 10 and 0.52 V for 11vs. SCE). The cyclic voltammogram of [FeCl2(NPN Me2-N,N)] showed a reversible redox couple at -0.17 V vs. SCE assigned to the oxidation of the Fe(ii) atom and an irreversible process at 0.65 V. The complexes 6, 8-11 and [FeCl2(NPNMe2-N,N)] have been evaluated in the catalytic oligomerization of ethylene with AlEtCl 2 or MAO as cocatalyst. The nickel complex 6 proved to be the most active precatalyst in the series, with a turnover frequency (TOF) of 61 800 molC2H4 molNi-1 h -1 with 10 equiv. of AlEtCl2 and 12 200 mol C2H4 molNi-1 h-1 with 200 equiv. of MAO. Precatalysts 8 and 9 were the most selective in butenes, up to 90% with 6 equiv. of AlEtCl2 and 89% with 2 equiv. of AlEtCl 2, respectively, and up to 92% butenes with 400 equiv. of MAO and 91% butenes with 200 equiv. MAO, respectively. The best selectivities for 1-butene were provided by 8 and AlEtCl2 (up to 31% with 6 equiv.) and 9 with MAO (up to 72% with 200 equiv.). The iron complexes were not significantly active with AlEtCl2 or MAO as cocatalyst. The Royal Society of Chemistry 2008.
