Chromium complexes bearing amidinato-phosphino ligand: synthesis, characterization, and catalytic properties of ethylene tri-/tetramerization and polymerization

An amidinato-phosphino ligand ArN[double bond, length as m-dash]C(R)NH(o-Ph₂PC₆H₄) (Ar = 2,4,6-Me₃C₆H₂, R = Ph (1); Ar = 2,6-iPr₂C₆H₃, R = Ph (2); Ar = 2,6-iPr₂C₆H₃, R = tBu (3)) was prepared. The ligand reacted with CrCl₃(THF)₃ to yield the N,P-chelation complex [ArNHC(R)[double bond, length as m-dash]N(o-Ph₂PC₆H₄)]CrCl₃(THF) (4-6), and the ligand's lithium salt ArN[double bond, length as m-dash]C(R)N(o-Ph₂PC₆H₄)Li reacted with the respective CrCl₃(THF)₃ and CrCl₂(THF)₂ to give the N,N,P-chelation complexes [ArN[double bond, length as m-dash]C(R)N(o-Ph₂PC₆H₄)]CrCl₂(THF) (7-8) and {[ArN[double bond, length as m-dash]C(R)N(o-Ph₂PC₆H₄)]Cr(μ-Cl)}₂ (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.