Some novel monoalkyl-N-aryl-substituted iminopyridine iron chloride complexes, differing in the nature of the substituent at the iminic carbon and at the ortho position of the aryl ring, were synthesized and characterized. For one of them, single crystals were obtained, which allowed for the determination of its crystalline structure, in which the iron center is coordinated to the chlorides and to the two nitrogen atoms of the ligand. The coordination around iron is distorted tetrahedral, a coordination mode rarely identified for FeCl2 adducts with bidentate nitrogen ligands. All the complexes were used, in combination with methylaluminoxane, for the polymerization of 1,3-butadiene and isoprene, providing syndiotactic 1,2 poly­(1,3-butadiene)­s and poly­(isoprene)­s with a predominantly cis-1,4/3,4 alternating structure, in which short cis-1,4 sequences of three or five units, whose length depends on the nature of the ligand on the iron atom, are present. A detailed NMR characterization (1H-, 13C-, and 2D experiments) of the resultant poly­(isoprene)­s is reported, and a tentative scheme for the formation of the novel isoprene polymers is proposed.

α,ω-Dienes are an important class of monomers due to their utility in the synthesis of cyclopolyolefins and reactive polyolefin intermediates. In this contribution, the terpolymerization of two α,ω-dienes (i.e., 1,5-hexadiene and 1,7octadiene) with ethylene and various cyclic olefins [i.e., norbornene (NB), 5ethylidene-2-norbornene (ENB), and dicyclopentadiene (DCPD)] catalyzed by a chelated imido vanadium complex has been examined. The ENB and DCPD diene termonomers provide additional sites for post-polymerization functionalization. Vanadium-catalyzed terpolymerization of the investigated α,ω-dienes yields polyolefins with a high molecular weight (M w up to 200 × 10 3 g mol −1 ), unimodal and narrow molecular weight distribution, subambient glass transition temperatures (−30 < T g °C < −3), and a proper content of CC bonds. Comprehensive NMR investigation of the obtained polymers revealed that subtle changes in the α,ω-diene size have important effects on the numerous combinations of insertion paths (ring closure vs ring opening), from which different repeating units with a CC bond in the side or main polymer chain and cyclic units are installed. Finally, the poly(ethylene-ter-1,5-hexadiene-ter-NB) was subjected to thiol-ene addition using thioglycolic acid, methyl thioglycolate, and N-acetyl-L-cysteine to access polar-functionalized polyolefins with a degree of functionalization and properties dependent on the thiol substitution.

The fabrication of polyolefin thermoplastic elastomers (P-TPEs) with superior robustness (high strength and high toughness) is challenging. Integrating dynamic (reversible) noncovalent cross-links into P-TPEs may solve the trade-off between strength and toughness and permanent (irreversible) cross-linking and elasticity. Here, we report a two-step synthesis of P-TPEs that contain flexible polymer chains and different thiol branches (less than 2.0 mol %) that cross-link the polymer chains through dynamic hydrogen bonding. The cross-linked polymers exhibit negligible hysteresis after being circularly stretched 10 times at low strain, that is, few dynamic H-bonds break per cycle and delocalize the stress concentration to withstand load and delay premature fracture. At large deformation, the polymers dissipate vast stress energy by the sacrificial H-bond scission: the H-bonds break and reform to prevent failure and to dictate simultaneously high fracture strength (σ up to 10.2 MPa) and high toughness (U T up to 22.6 MJ/m3). Meanwhile, the resultant materials present low stiffness (E ≈ 2.5 MPa), good extensibility (ε > 600%), and elastic recovery of 90% even at 680% strain. The cross-linked polyolefins are readily (re)­processable, and tensile and elastic properties are largely recovered after being remolded at least twice.

Some novel cobalt diphenylphosphine complexes were synthesized by reacting cobalt(II) chloride with (2-methoxyethyl)diphenylphosphine, (2-methoxyphenyl)diphenylphosphine, and 2-(1,1-dimethylpropyl)-6-(diphenylphosphino)pyridine. Single crystals suitable for X-ray diffraction studies were obtained for the first two complexes, and their crystal structure was determined. The novel compounds were then used in association with methylaluminoxane (MAO) for the polymerization of 1,3-butadiene, and their behavior was compared with that exhibited in the polymerization of the same monomer by the systems CoCl2(PnPrPh2)2/MAO and CoCl2(PPh3)2/MAO. Some significant differences were observed depending on the MAO/Co ratio used, and a plausible interpretation for such a different behavior is proposed.

β-ketoimines are extensively applied for the synthesis of organometallic complexes intended as (pre)catalysts for a variety of chemical transformations. We were interested in the synthesis of two Cr complexes bearing a simple bidentate β-ketoimine (L), with different ligand binding modes, as well as their application as a precatalyst in the polymerization of olefins. Complex 1 (L2CrCl3) was obtained by direct reaction of L with CrCl3(THF)3, while, for the synthesis of complex 2 (LCrCl2), the ligand was first deprotonated with nBuLi, giving the β-ketoiminato ligand L─Li+, and then reacted with CrCl3(THF)3. Characterization of the complexes proved that the Cr(III) ion is coordinatively bonded to L in 1, while it is covalently bonded to L in 2. The complexes were then used as precatalysts for the polymerization of ethylene and various cyclic olefins. Upon activation with methylaluminoxane, both the complexes exhibited poor activity in the polymerization of ethylene, whilst they exhibit good productivity in the polymerization of cyclic olefins, affording semicrystalline oligomers, without a significant difference between 1 and 2. To gain more insight, we investigated the reaction of the complexes with the Al-cocatalyst by IR and UV-Vis spectroscopies. The results proved that, in case of 1, the Al-activator deprotonates the ligand, bringing to the formation of an active species analogous to that of 2.