Addition of BF 3 .Et 2 O to {[(C 6 H 5 ) 2 PC 6 H 4 (μ-CO 2 )-κ 3 P,O,O']Ni(η 1 -CH 2 C 6 H 5 )} 2 gives [(C 6 H 5 ) 2 PC 6 H 4 C(O BF 3 )O-κ 2 P,O]Ni(η 3 -CH 2 C 6 H 5 ) (4). The single crystal structure of 4 is consistent with substantial positive charge at the nickel atom. Addition of ethylene to solutions of 4 in toluene provides ethylene oligomers. The average molecular weight of the products is larger than that of the oligomers obtained using [(C 6 H 5 ) 2 PC 6 H 4 C(OB(C 6 F 5 ) 3 )O-κ 2 P,O]Ni(η 3 -CH 2 C 6 H 5 ) (1). When 2 equiv. of Et 2 O.BF 3 are added to {(H 3 C)C[N(2,6-(CHMe 2 ) 2 C 6 H 3 )]C(O)[N(2,6-(CHMe 2 ) 2 C 6 H 3 )]-κ 2 N,O}N i(η 1 -CH 2 C 6 H 5 )(PMe 3 ) (5) one obtains {(H 3 C)C[N(2,6-(CHMe 2 ) 2 C 6 H 3 )]C[O BF 3 ][N(2,6-(CHMe 2 ) 2 C 6 H 3 )]-κ 2N,N'}Ni(η 3 -CH 2 C 6 H 5 ) (7). Two isomers of 7 are observed by NMR spectroscopy and are incorporated into the crystal lattice, as shown by X-ray diffraction studies. Polyethylene is obtained upon exposure of a solution of 7 to ethylene. Active species can also be generated in situ by addition of BF 3 gas, Et 2 O.BF 3 or t BuMeO.BF 3 to 5.