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An amidinato-phosphino ligand ArN[double bond, length as m-dash]C(R)NH(o-PhPCH) (Ar = 2,4,6-MeCH, R = Ph (1); Ar = 2,6-iPrCH, R = Ph (2); Ar = 2,6-iPrCH, R = tBu (3)) was prepared. The ligand reacted with CrCl(THF) to yield the N,P-chelation complex [ArNHC(R)[double bond, length as m-dash]N(o-PhPCH)]CrCl(THF) (4-6), and the ligand's lithium salt ArN[double bond, length as m-dash]C(R)N(o-PhPCH)Li reacted with the respective CrCl(THF) and CrCl(THF) to give the N,N,P-chelation complexes [ArN[double bond, length as m-dash]C(R)N(o-PhPCH)]CrCl(THF) (7-8) and {[ArN[double bond, length as m-dash]C(R)N(o-PhPCH)]Cr(μ-Cl)} (9-11). Complexes 1-11 were characterized by IR, NMR (for 1-3), EPR (for 4-11) spectroscopy and CHN elemental analysis, of which 3, 5, 8, and 11 were further studied by X-ray crystallography. Upon activation with an organoaluminum cocatalyst, complexes 4-6 were all catalytically active in ethylene tri-/tetramerization along with ethylene polymerization, and complexes 7-11 functioned as well but in ethylene polymerization. The correlation between the structure and the catalytic properties of the catalyst system is discussed.

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