Monometallic and Bimetallic Titanium κ1‑Amidinate Complexes as Olefin Polymerization Catalysts

A series of cyclopentadienyl-κ1-amidinate titanium complexes Cp*Ti­{NC­(ArR)­NiPr2}­Me2 (ArR = 4-C6H4R, where R = H (1-Me), CF3 (5-Me), tBu (6-Me), or NMe2 (7-Me)) with different para-substituents in the amidinate ligand were synthesized and structurally characterized, along with three bimetallic analogues: 1,4-C6H4{C­(NiPr2)­N}2{Cp*TiMe2}2 (2-Me), 1,3-C6H4{C­(NiPr2)­N}2{Cp*TiMe2}2 (3-Me), and CH2{1,4-C6H4-C­(NiPr2)­N}2{Cp*TiMe2}2 (4-Me). 13C NMR spectroscopy, density function theory, and the quantum theory of atoms-in-molecules were used to evaluate the donor ability of the various NC­(Ar R)­NiPr2 ligands and the influence of the ArR group para-substituents. Reactions of 1-Me and certain homologues, as well as 2-Me, with borate and borane reagents [CPh3]­[BArF4] (ArF = C6F5), BArF3, in the absence or presence of Lewis bases or polar unsaturated substrates were carried out, forming adducts and migratory insertion products such as [Cp*Ti­{NC­(Ph)­NiPr2}­Me­(THF)]­[BArF4], [Cp*Ti­{NC­(Ph)­NiPr2}­{MeC­(NiPr)2}]­[BArF4], and [1,4-C6H4{C­(NiPr2)­N}2{Cp*Ti­{MeC­(NiPr)2}2][BArF4]2. Detailed olefin copolymerization studies for forming EPDM from ethylene, propylene, and certain dienes were carried out with mono- and bimetallic catalysts and borate and borane activators. Catalyst–activator effects on polymerization productivity and polymer composition relationships were mapped. Bimetallic catalysts 2 and 3 showed cooperative effects based on electronic factors, leading to enhanced propene incorporation, but unfavorable steric effects gave lower diene content. Related but less significant electronic effects on propene affinity were found for the monometallic catalysts Cp*Ti­{NC­(ArR)­NiPr2}­Me2 as the ArR moiety para-substituents were varied.