The complex (μ-Me 2 C-3,3′){(η 5 -cyclopentadienyl)[1-Me 2 Si-( t BuN)](TiMe 2 )} 2 (3) was prepared as a new binuclear catalyst motif for homogeneous olefin polymerization. Complex 3 exists as rac-3 and meso-3 diastereomers, which can be separated and characterized by solution NMR spectroscopy and single-crystal X-ray diffraction. While meso-3 has high thermal stability, rac-3 undergoes thermolysis in solution to quantitatively form the dimeric methylidene complex (μ-Me 2 C-3,3′){(η 5 -cyclopentadienyl)[1-Me 2 Si( t BuN)][(μ-CH 2 )Ti]} 2 (rac-4). Activation of rac-3 and meso-3 with 1 equiv of Ph(5; rac-5 and meso-5, respectively). Interestingly, meso-5 is stable in the presence of an additional 1 equiv of Ph] 2 (rac-6) as indicated by multinuclear NMR spectroscopy and DFT computation. meso-3 reacts with 2 equiv of B(C 6 F 5 ) 3 to yield meso-[(μ-CMe 2 -3,3′){(η 5 -cyclopentadienyl)[1-Me 2 Si( t BuN)]} 2 (μ-CH 2 )(μ-CH 3 )Ti 2 ] + MeB(C 6 F 5 ) 3 − (meso-7) containing the same meso-5 cation but with a MeB(C 6 F 5 ) 3 − counteranion. These findings, along with catalytic results, indicate that rac-3 and meso-3 remain structurally intact during polymerization, consistent with the observed diastereoselectivity effects. Under identical ethylene/1octene copolymerization conditions, only activated bimetallic rac-3 produces appreciable polymer, with meso-3 exhibiting low activity, but both yield polymer with a branch density >2× that of the monometallic control [(3-t Bu-C 5 H 3 )SiMe 2 N t Bu]TiMe 2 (Ti 1 ). In ethylene/styrene copolymerizations, rac-3 produces polymers with 3.1× higher M n and 2.1× greater styrene incorporation versus Ti 1 , while meso-3 catalyzes only ethylene-free styrene homopolymerization. In 1-octene homopolymerizations, meso-3 + B(C 6 F 5 ) 3 (i.e., meso-7) produces highly isotactic poly-1-octene (mmmm 91.7%), while rac-3 + Ph 3 C + B(C 6 F 5 ) 4 − (i.e., rac-5), rac-3 + B(C 6 F 5 ) 3 (i.e., rac-7), and meso-3 + Ph 3 C + B(C 6 F 5 ) 4 − (i.e., meso-5) produce only atactic poly-1-octene. These bimetallic polymerization catalysts exhibit distinctive cooperative effects influencing product M n , tacticity, and comonomer selection, demonstrating that binuclear catalyst stereochemical factors are significant.

An unsymmetrical bimetallic catalyst, (CF 3 / SO 2 )FI 2 -Ni 2 , having a CF 3 -functionalized phenoxyiminato Ni(II) center, which produces linear high-M w polyolefin (CF 3 /Ni) joined to an adjacent SO 2 -functionalized phenoxyiminato Ni(II) center, which produces highly branched low-M w polyolefin (SO 2 /Ni), was synthesized and fully characterized. In ethylene homopolymerizations, (CF 3 /SO 2 )FI 2 -Ni 2 affords monomodal (Đ = 1.7), highly, long-chain branched (69 branches/1000 C) polyethylenes with M w = 24 kg/mol. In contrast, bimetallic (CF 3 )FI 2 -Ni 2 and (SO 2 )FI 2 -Ni 2 produce high-M w (25 kg/mol) exclusively methyl-branched (40 branches/1000 C) and low-M w (4.5 kg/mol) highly branched (105 branches/1000 C) polyethylenes, respectively, while tandem monometallic (CF 3 )FI-Ni + (SO 2 )FI-Ni catalyst mixtures yield a bimodal polyolefin mixture (Đ = 6.4).

The binuclear salphen Ti polymerization catalyst N,N′-1,2-phenylene­[(salicylideneaminato)­Ti­(Cp*)­Me2)]2 (2) is synthesized by reaction of salphen-H2 with Cp*TiMe3. Mononuclear [N-(2,6-diisopropyl)­phenyl­(salicylidene­aminato)]­Ti­(Cp*)­Me2 (1) serves as a control. Activation studies of 2 with cocatalyst Ph3C+­B­(C6F5)4 – yield the cationic polymerization-inactive complex [N,N′-1,2-phenylene­(salicylidene­aminato)­Ti­(Cp*)]+­B­(C6F5)4 – (4) and polymerization-active Cp*TiMe2 +­B­(C6F5)4 –. Polymerization studies comparing 2 with Cp*TiMe 3 suggest that, within the catalytic time frame, while 2 retains bimetallic character under an ethylene atmosphere, it rapidly decomposes to 4 and Cp*TiMe2 + in the presence of 1-hexene. These monomer-dependent reorganization results highlight the importance of olefin polymerization activation mechanistic studies while providing insight for improved bimetallic catalyst design.