Me 2 NC 2 H 4 C 5 Me 4 Li reacts with Cr(THF) 3 Cl 3 to give (η 1 :η 5 -Me 2 NC 2 H 4 C 5 Me 4 )CrCl 2 , in which the complexation of the N-donor atom to the metal atom has been confirmed by X-ray crystallography. A series of related compounds, e.g. (η 1 :η 5 -cyclo-C 4 H 8 NSiMe 2 OSiMe 2 C 5 H 4 )-CrCl 2 , has been prepared by varying the substituents on the organic ligand. Further reaction with organomagnesium reagents leads to formation of the corresponding dialkyl-Cr complexes. Related species have been prepared containing imine-, alkoxy-, and alkylthiosubstituted cyclopentadienyl groups as well as the C-donor ligand tetramethylimidazol-2ylidene. Treatment of these compounds with methylalumoxane (MAO) leads to the formation of highly active catalysts for the oligomerization, polymerization, and copolymerization of ethylene.