Synthesis of cobalt(II) and iron(II) complexes with the ligand bis(2-diphenylphosphinoethyl)methylamine and their catalytic action on ethylene oligomerization. X-ray crystal structure of [CoCl2{CH3N(CH2CH2PPh2)2}]

Complexes [MCl2{CH3N(CH2CH2PPh2)2}] (1, M=Co; 2, Fe) were prepared by a modified procedure. The X-ray structural determination of 1 reveals that the cobalt(II) complex is four-coordinate with a distorted tetrahedral coordination geometry. The tertiary amine CH3N(CH2CH2PPh2)2 acts as a bidentate ligand through two phosphorus atoms. The CoP distances of 2.3666(14) and 2.3731(15) Å found in 1 are significantly longer than general CoP bond lengths. The incoordinate N atom of the ligand locates at the apical position trans to one of the chlorides. The catalytic properties of 1 and 2 in combination with ethylaluminoxane (EAO) as cocatalyst for ethylene oligomerization were studied. The activities of 89.4 kg oligomers mol−1 Co h−1 for 1 and 81.2 kg oligomers mol−1 Fe h−1 for 2 (100 equivalents of EAO, 180 °C and 1.8 MPa ethylene) were observed with high selectivity to linear C4–10 olefins.