Complexes [MCl 2 {CH 3 N(CH 2 CH 2 PPh 2 ) 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 CH 3 N(CH 2 CH 2 PPh 2 ) 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 oligomersmol - 1 Coh - 1 for 1 and 81.2 kg oligomersmol - 1 Feh - 1 for 2 (100 equivalents of EAO, 180 o C and 1.8 MPa ethylene) were observed with high selectivity to linear C 4 - 1 0 olefins.