Search Results (3)

Four examples of N,N-bis(aryl)butane-2,3-diimine–nickel(II) bromide complexes, [ArN=C(Me)-C(Me)=NAr]NiBr₂ (where Ar = 2-(C₅H₉)-4,6-(CHPh₂)₂C₆H₂ (Ni1), Ar = 2-(C₆H₁₁)-4,6-(CHPh₂)₂C₆H₂ (Ni2), 2-(C₈H₁₅)-4,6-(CHPh₂)₂C₆H₂ (Ni3) and 2-(C₁₂H₂₃)-4,6-(CHPh₂)₂C₆H₂ (Ni4)), disparate in the ring size of the ortho-cycloalkyl substituents, were prepared using a straightforward one-pot synthetic method. The molecular structures of Ni2 and Ni4 highlight the variation in the steric hindrance of the ortho-cyclohexyl and -cyclododecyl rings exerted on the nickel center, respectively. By employing EtAlCl₂, Et₂AlCl or MAO as activators, Ni1–Ni4 displayed moderate to high activity as catalysts for ethylene polymerization, with levels falling in the order Ni2 (cyclohexyl) > Ni1 (cyclopentyl) > Ni4 (cyclododecyl) > Ni3 (cyclooctyl). Notably, cyclohexyl-containing Ni2/MAO reached a peak level of 13.2 × 10⁶ g(PE) of (mol of Ni)⁻¹ h⁻¹ at 40 °C, yielding high-molecular-weight (ca. 1 million g mol⁻¹) and highly branched polyethylene elastomers with generally narrow dispersity. The analysis of polyethylenes with ¹³C NMR spectroscopy revealed branching density between 73 and 104 per 1000 carbon atoms, with the run temperature and the nature of the aluminum activator being influential; selectivity for short-chain methyl branches (81.8% (EtAlCl₂); 81.1% (Et₂AlCl); 82.9% (MAO)) was a notable feature. The mechanical properties of these polyethylene samples measured at either 30 °C or 60 °C were also evaluated and confirmed that crystallinity (X_c) and molecular weight (M_w) were the main factors affecting tensile strength and strain at break (ε_b = 353–861%). In addition, the stress–strain recovery tests indicated that these polyethylenes possessed good elastic recovery (47.4–71.2%), properties that align with thermoplastic elastomers (TPEs). Full article

Five examples of bis(arylimino)tetrahydrocyclohepta[b]pyridine dichloroiron(II) complex, [2-{(Ar)N=CMe}-9-{N(Ar)}C₁₀H₁₀N]FeCl₂ (Ar = 2-(C₅H₉)-4,6-(CHPh₂)₂C₆H₂Fe1, 2-(C₆H₁₁)-4,6-(CHPh₂)₂C₆H₂Fe2, 2-(C₈H₁₅)-4,6-(CHPh₂)₂C₆H₂Fe3, 2-(C₁₂H₂₃)-4,6-(CHPh₂)₂C₆H₂Fe4, and 2,6-(C₅H₉)2-4-(CHPh₂)C₆H₂Fe5), incorporating ortho-pairings based on either benzhydryl/cycloalkyl (ring sizes ranging from 5 to 12) or cyclopentyl/cyclopentyl groups, have been prepared in reasonable yield by employing a simple one-pot template strategy. Each complex was characterized by FT-IR spectroscopy, elemental analysis, and for Fe3 and Fe5 by single crystal X-ray diffraction; pseudo-square pyramidal geometries are a feature of their coordination spheres. On treatment of Fe1–Fe5 with modified methylaluminoxane (MMAO) or methylaluminoxane (MAO), a range in catalytic activities for ethylene polymerization were observed with benzhydryl/cyclopentyl-containing Fe1/MMAO achieving the maximum level of 15.3 × 10⁶ g PE mol⁻¹ (Fe) h⁻¹ at an operating temperature of 70 °C. As a key trend, the activity was found to drop as the ortho-cycloalkyl ring size increased: Fe1_C5H9/CHPh2~Fe5_C5H9/C5H9 > Fe2_C6H11/CHPh2 > Fe3_C8H15/CHPh2 > Fe4_C12H23/CHPh2. Furthermore, strictly linear polyethylenes (T_m > 126 °C) were formed with molecular weights again dependent on the ortho-cycloalkyl ring size (up to 55.6 kg mol⁻¹ for Fe1/MAO); narrow dispersities were a characteristic of all the polymers (M_w/M_n range: 2.3–4.7), highlighting the well-controlled nature of these polymerizations. Full article

Six examples of 2-(1-arylimino)ethyl-9-arylimino-5,6,7,8-tetrahydrocycloheptapyridine-cobalt(II) chloride complexes, [2-(1-ArN)C₂H₃-9-ArN-5,6,7,8-C₅H₈C₅H₃N]CoCl₂, (Ar = 2-(C₅H₉)-6-MeC₆H₃ Co1, 2-(C₆H₁₁)-6-MeC₆H₃ Co2, 2-(C₈H₁₅)-6-MeC₆H₃ Co3, 2-(C₅H₉)-4,6-Me₂C₆H₂ Co4, 2-(C₆H₁₁)-4,6-Me₂C₆H₂ Co5, and 2-(C₈H₁₅)-4,6-Me₂C₆H₂ Co6), were synthesized by the direct reaction of the corresponding ortho-cycloalkyl substituted carbocyclic-fused bis(arylimino)pyridines (L1–L6) and cobalt(II) chloride in ethanol with good yields. All the synthesized ligands (L1–L6) and their corresponding cobalt complexes (Co1–Co6) were fully characterized by FT-IR, ¹H/¹³C-NMR spectroscopy and elemental analysis. The crystal structure of Co2 and Co3 revealed that the ring puckering of both the ortho-cyclohexyl/cyclooctyl substituents and the one pyridine-fused seven-membered ring; a square-based pyramidal geometry is conferred around the metal center. On treatment with either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), all the six complexes showed high activities (up to 4.09 × 10⁶ g of PE mol⁻¹ (Co) h⁻¹) toward ethylene polymerization at temperatures between 20 °C and 70 °C with the catalytic activities correlating with the type of ortho-cycloalkyl substituent: Cyclopentyl (Co1 and Co4) > cyclohexyl (Co2 and Co5) > cyclooctyl (Co3 and Co6) for either R = H or Me and afforded strictly linear polyethylene (T_m > 130 °C). The narrow unimodal distributions of the resulting polymers are consistent with single-site active species for the precatalyst. Furthermore, compared to the previously reported cobalt analogues, the titled precatalysts exhibited good thermo-stability (up to 70 °C) and possessed longer lifetime along with a higher molecular weight of PE (M_w: 9.2~25.3 kg mol⁻¹). Full article