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The N, N, N′-ferrous chloride complexes, [2-{CMeN(2,4-(CHPh)2-6-FC6H2)}-6-(CMeNAr)C5H3N]FeCl2 (Ar = 2,6-Me2C6H3Fe1, 2,6-Et2C6H3Fe2, 2,6-iPr2C6H3Fe3, 2,4,6-Me3C6H2Fe4 and 2,6-Et2-4-MeC6H2Fe5), each possessing one N-2,4-dibenzhydryl-6-fluorophenyl group, were readily synthesized from their respective unsymmetrical bis(imino)pyridines, L1–L5. Structural identification of Fe2 highlighted the variation in the steric properties provided by the dissimilar N-aryl groups. Following pre-treatment with either MAO or MMAO, complexes Fe1–Fe5 all displayed, at an operating temperature of 80 °C, high activities for ethylene polymerization with levels falling in the order: Fe4 > Fe1 > Fe5 > Fe2 > Fe3. Notably, Fe4/MAO displayed the highest activity of 1.94×107 gPE·molFe−1·h−1 of the study with only a modest loss in performance at 90 °C. Generally, the resulting polyethylenes were highly linear (Tm range: 122–132 °C), narrowly disperse and of low molecular weight (Mw range: 6.73–46.04 kg·mol−1), with the most sterically hindered Fe3 forming the highest molecular weight polymer of the series. End-group analysis by 1H- and 13C-NMR spectroscopy revealed saturated alkyl (n-propyl and i-propyl) and unsaturated vinyl chain ends indicative of the role of both β-H elimination and chain transfer to aluminum as termination pathways. By comparison with previously reported iron precatalysts with similar tridentate ligand skeletons, it is evident that the introduction of a large benzhydryl group in combination with a fluorine as the ortho-substituents of one N-aryl group has the effect of enhancing thermal stability of the iron polymerization catalyst whilst maintaining appreciable polymer molecular weight. [ABSTRACT FROM AUTHOR]

Unsymmetrical 11-phenyl-1,2,3,7,8,9,10-heptahydrocyclohepta[b]quinoline-4,6-dione, incorporating a para-phenyl substituted pyridine unit fused by both 6- and 7-membered carbocyclic rings, has been prepared on the gram-scale via a multi-step procedure involving cyclization, hydrogenation and oxidation. Templating this diketone, in the presence of cobalt(II) chloride hexahydrate, with the corresponding aniline afforded in good yield five examples of doubly fused bis(arylimino)pyridine-cobalt(II) chlorides, Co1 (aryl = 2,6-dimethylphenyl), Co2 (2,6-diethylphenyl), Co3 (2,6-diisopropylphenyl), Co4 (2,4,6-trimethylphenyl) and Co5 (2,6-diethyl-4-methylphenyl). Structural characterization of Co1, Co2 and Co3 highlights the flexible nature of the inequivalent fused rings on the NNN'-ligand and the skewed disposition of the para-phenyl group. On activation with MAO, Co1–Co5 exhibited high activity for ethylene polymerization at 30 °C (up to 5.66 × 106 g (PE) mol−1 (Co) h−1) with the relative order being as follows: Co4 > Co1 > Co5 > Co3 > Co2. All polyethylenes were strictly linear, while their molecular weights and dispersities showed some notable variations. For Co1, Co2, Co4 and Co5, all polymerizations were well controlled as evidenced by the narrow dispersities of their polymers (Mw/Mn range: 1.8–2.7), while their molecular weights (Mw range: 2.9–10.9 kg mol−1) steadily increased in line with the greater steric properties of the N-aryl ortho-substituents. By contrast, the most hindered 2,6-diisopropyl counterpart Co3 displayed a broad distribution with bimodal characteristics (Mw/Mn = 10.3) and gave noticeably higher molecular weight polymer (Mw = 75.5 kg mol−1). By comparison, the MMAO-activated catalysts were generally less active, but showed similar trends in molecular weight and polymer dispersity. End group analysis of selected polymers via 13C and 1H NMR spectroscopy revealed the presence of both saturated and unsaturated polyethylenes in accordance with competing chain transfer pathways. Notably, when comparing Co3/MAO with its non-phenyl substituted analogue (E2,6-iPr2Ph)CoCl2/MAO, the former, though less controlled, displayed higher activity and molecular weight, a finding that points towards a role played by the remote para-phenyl group. [ABSTRACT FROM AUTHOR]

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 (Xc) and molecular weight (Mw) were the main factors affecting tensile strength and strain at break (εb = 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). [ABSTRACT FROM AUTHOR]

Six different examples of 4,4′-dichlorobenzhydryl-substituted 2,6-bis(arylimino)pyridyl-iron(II) chloride complex, [2-{{2,6-((p-ClPh)2CH)2-4-MeC6H2}N＝CMe}-6-(ArN＝CMe)C5H3N]FeCl2 (Ar = 2,6-Me2C6H3Fe1, 2,6-Et2C6H3Fe2, 2,6-iPr2C6H3Fe3, 2,4,6-Me3C6H2Fe4, 2,6-Et2-4-MeC6H2Fe5, 2,6-((p-ClPh)2CH)2-4-MeC6H2Fe6), have been synthesized in good yield and characterized by various spectroscopic and analytical techniques. The molecular structures of Fe2 and Fe5 emphasize the uneven steric protection of the ferrous center imposed by the unsymmetrical N,N,N′-chelate. When treated with either MAO or MMAO (modified-MAO) as activators, Fe1–Fe5 exhibited very high productivities at elevated temperature with peak performance of 21.59 × 106 g PE mol−1(Fe) h−1 for Fe5/MMAO at 50 °C and 15.65 × 106 g PE mol−1(Fe) h−1 for Fe1/MAO at 60 °C. By contrast, the most sterically hindered Fe6 was either inactive (using MAO) or displayed very low activity (using MMAO). As a further feature, this class of iron catalyst was capable of displaying long lifetimes with catalytic activities up to 10.77 × 106 g PE mol−1(Fe) h−1 observed after 1 h. In all cases, strictly linear and unimodal polyethylene was formed with narrow dispersity, while the polymer molecular weight was strongly influenced by the aluminoxane co-catalyst (Mw using MAO > MMAO) and also by the steric properties of the second N-aryl group (up to 32.9 kg mol−1 for Fe3/MAO). [ABSTRACT FROM AUTHOR]

The cobalt(II) chloride N,N,N-pincer complexes, [2-{(2,4-(C15H13)2-6-FC6H2)N=CMe}-6-(ArN=CMe)C5H3N]CoCl2 (Ar = 2,6-Me2C6H3) (Co1), 2,6-Et2C6H3 (Co2), 2,6-i-Pr2C6H3 (Co3), 2,4,6-Me3C6H2 (Co4), 2,6-Et2-4-MeC6H2 (Co5), and [2,6-{(2,4-(C15H13)2-6-FC6H2)N=CMe}2C5H3N]CoCl2 (Co6), each containing at least one N-2,4-bis(dibenzosuberyl)-6-fluorophenyl group, were synthesized in good yield from their corresponding unsymmetrical (L1–L5) and symmetrical bis(imino)pyridines (L6). The molecular structures of Co1 and Co2 spotlighted their distorted square pyramidal geometries (τ5 value range: 0.23–0.29) and variations in steric hindrance offered by the dissimilar N-aryl groups. On activation with either MAO or MMAO, Co1–Co6 all displayed high activities for ethylene polymerization, with levels falling in the order: Co1 > Co4 > Co5 > Co2 > Co3 > Co6. Indeed, the least sterically hindered 2,6-dimethyl Co1 in combination with MAO exhibited a very high activity of 1.15 × 107 g PE mol−1 (Co) h−1 at the operating temperature of 70 °C, which dropped by only 15% at 80 °C and 43% at 90 °C. Vinyl-terminated polyethylenes of high linearity and narrow dispersity were generated by all catalysts, with the most sterically hindered, Co3 and Co6, producing the highest molecular weight polymers [Mw range: 30.26–33.90 kg mol−1 (Co3) and 42.90–43.92 kg mol−1 (Co6)]. In comparison with structurally related cobalt catalysts, it was evident that the presence of the N-2,4-bis(dibenzosuberyl)-6-fluorophenyl groups had a limited effect on catalytic activity but a marked effect on thermal stability. [ABSTRACT FROM AUTHOR]

Four types of benzhydryl‐containing bis(arylimino)pyridine‐iron(II) chloride complex, [2‐{CMeN(2,4,6‐Me3C6H2)}‐6‐{CMeN(Ar)}C5H3N]FeCl2 (Ar=2,4‐(CHPh2)2‐6‐(C5H9)C6H2Fe1, 2,4‐(CHPh2)2‐6‐(C6H11)C6H2Fe2, 2,4‐(CHPh2)2‐6‐(C8H15)C6H2Fe3 and 2,4‐(CHPh2)2‐6‐(C12H23)C6H2Fe4), discriminable by the ring size of the ortho‐CnH2n−1 (n=5, 6, 8, 12) group, have been prepared in good yield (>85 %) via the reaction of the corresponding N,N,N′‐ligand, L1–L4, with ferrous chloride tetrahydrate. All new complexes were characterized by FT‐IR spectroscopy and elemental analysis. The molecular structure of Fe3 emphasizes the distorted pseudo‐square pyramidal geometry bestowed to the metal center and the steric unevenness provided by the inequivalent N‐mesityl and N‐2,4‐dibenzyhydryl‐6‐cyclooctylphenyl groups. Extremely high activities for ethylene polymerization were achieved at temperatures between 60 °C and 70 °C following pre‐treatment of the iron(II) precatalyst with either MMAO or MAO, with the relative performance being: Fe2>Fe1>Fe3>Fe4. Notably, ortho‐cyclohexyl Fe2, under activation with MMAO, afforded the highest level of performance of this study reaching 2.82×107 g PE per mol (Fe) per h at 70 °C forming strictly linear and narrowly dispersed polyethylene (Mw/Mn=2.0) with moderate molecular weight (11.3 kg per mol). Furthermore, runs performed using Fe1/MMAO at 90 °C saw the catalytic activity drop by around only 40 % highlighting the remarkable thermostability of these catalysts. By comparison, polymerizations performed using MAO as co‐catalyst were less controlled with broader dispersities (Mw/Mn range: 4.8–10.1), while the molecular weights were generally higher (55.7–150.9 kg per mol). [ABSTRACT FROM AUTHOR]

Four unsymmetrical examples of bis(arylimino)pyridines that each possess an ortho‐cycloalkyl substituent of unique ring size, 2‐{CMeN(2,4,6‐Me3C6H2)}‐6‐{CMeN(2,4‐(CHPh2)2‐6‐RC6H2)}C5H3N (R = cyclopentyl L1, cyclohexyl L2, cyclooctyl L3, cyclododecyl L4), have been prepared and employed as reactants in the formation of the corresponding cobaltous chloride complexes, (N,N,N′)CoCl2 (Co1–Co4). Structural characterization of Co2 and Co3 spotlights the five‐coordinate geometry and the steric disparity imposed on the metal center by the inequivalent N‐mesityl and N‐2,4‐dibenzyhydryl‐6‐cycloalkylphenyl groups. Co1–Co4 all proved productive precatalysts for ethylene polymerization achieving optimal performance at a temperature of 60°C on activation with either MAO or MMAO. Cyclopentyl‐containing Co1 displayed the highest level (up to 10.3 × 106 g PE per mol [Co] per h), whereas its cyclododecyl counterpart Co4 the lowest (down to 0.14 × 106 g PE per mol [Co] per h). Strictly linear polyethylenes were produced with molecular weights spanning the range 22.0–36.0 kg per mol for Co1–Co4/MAO and 22.6–33.6 kg per mol for Co1–Co4/MMAO, with cyclohexyl Co2 producing the highest values with either activator. With the exception of the polymer produced using Co4, all catalysts afforded narrow unimodal distributions (Mw/Mn range: 1.7–2.2) for the polyethylenes in line with single site active species. By contrast, Co4 bearing the largest and conformationally flexible cycloalkyl group formed polyethylenes that were distinctly bimodal, which would imply the presence of two active species. End‐group analysis of lower molecular weight polymer samples identified vinyl groups congruent with a termination step involving β‐H elimination. [ABSTRACT FROM AUTHOR]

Condensation of 2‐benzoyl‐6,7‐dihydro‐5H‐quinolin‐8‐one with an excess of the respective fluorinated aniline in the presence of cobalt (II) chloride has provided an effective one‐flask synthesis of the 2‐(phenyl(arylimino)methyl)‐8‐arylimino‐6,7‐dihydro‐5H‐quinoline‐cobalt (II) chloride complexes, [2‐(ArN=CPh)‐8‐(NAr)‐C9H9N]CoCl2 (Ar = 2‐Me‐4,6‐(CH(p‐FC6H4)2)2C6H2Co1, 2,6‐Me2‐4‐(CH(p‐FC6H4)2)C6H2Co2, 2,4‐Me2‐6‐(CH(p‐FC6H4)2)C6H2Co3, 2‐Et‐4,6‐(CH(p‐FC6H4)2)2C6H2Co4, 2‐i‐Pr‐4,6‐(CH(p‐FC6H4)2)2C6H2Co5, 2‐F‐4,6‐(CH(p‐FC6H4)2)2C6H2Co6). Structural characterization of Co2 and Co4 revealed the unsymmetrical nature of the N,N,N‐chelating ligands and the five‐coordinate geometries around the metal ions. Complexes Co1–Co6 all exhibited high activities as precatalysts for ethylene polymerization when treated with either MAO or MMAO producing highly linear (Tm′s > 118°C) low molecular weight polyethylene (Mw range: 0.69–31.51 kg mol−1) with a variety of dispersities (Mw/Mn range: 2.2–17.5). 2,6‐Dimethyl‐containing Co2 was the most productive precatalyst of the series reaching an exceptionally high activity of 27.06 × 106 g (PE) mol−1 (Co) h−1 at a temperature of 50°C. Additionally, ortho‐fluoride Co6 maintained an impressive level of activity at an operating temperature of 70°C and was able to maintain a long catalytic lifetime. Furthermore, the presence of vinyl end groups (–CH=CH2) in the 1H/13C NMR and IR spectra of their polymers supports the key role played by β‐H elimination in chain transfer. [ABSTRACT FROM AUTHOR]

A single‐pot method has been utilized to prepare the bis(cycloheptyl)fused N,N,N‐cobalt (II) chloride complexes, [2,3:5,6‐{C4H8C(NAr)}2C5H3N]CoCl2 (Ar = 2,6‐(C5H9)2–4‐(CHPh2)C6H2Co1, 2‐(C5H9)‐4,6‐(CHPh2)2C6H2Co2, 2‐(C6H11)‐4,6‐(CHPh2)2C6H2Co3, 2‐(C8H15)‐4,6‐(CHPh2)2C6H2Co4, 2‐(C12H23)‐4,6‐(CHPh2)2C6H2Co5) in reasonable yields. The molecular structure of Co1 highlights not only the steric shielding of the metal center provided by the N‐2,6‐dicyclopentyl‐4‐benzhydrylphenyl groups but also the trans‐configuration of the puckered sections of the two fused seven‐membered rings. Besides this structural characterization, all complexes have been characterized by elemental analysis and Fourier transform infrared spectroscopy (FT‐IR) spectroscopy. In the presence of modified methylaluminoxane (MMAO) or methylaluminoxane (MAO), Co1–Co5 afforded highly linear polyethylenes (Tm′s > 126°C) with dispersities that were influenced by the type of aluminoxane activator [Mw/Mn range: 1.53–1.81 (MMAO) vs. 8.96–15.5 (MAO)]. In common to both co‐catalysts, the catalytic activity of the precatalysts fell in the order: Co1 > Co2 > Co5 > Co4 ~ Co3, reflecting the differences in steric/electronic properties of the ortho‐cycloalkyl substituents. In terms of thermostability of the catalyst, Co1/MMAO attained optimal performance at 30°C (2.04 × 106 g PE mol−1[Co] h−1), while Co1/MAO reached it at 60°C albeit with lower productivity (0.70 × 106 g PE mol−1[Co] h−1). In general, the polyethylenes were of reasonably high molecular weight (e.g., between 39.9 and 65.8 kg mol−1 using MMAO) which can be linked to the steric hindrance imposed on chain transfer by the cycloalkyl and benzhydryl ortho‐substituents. Points: Cobalt (II) complexes bearing α,α'‐bis (imino)‐2,3:5,6‐bis (pentamethylene)pyridines appended with ortho‐cycloalkyl groups.A straightforward single‐pot template approach for complex synthesis.High activity and appreciable thermal stability for ethylene polymerization.Formation of highly linear polyethylenes. [ABSTRACT FROM AUTHOR]

Six examples of N,N,N‐chelated iron(II) chloride complex, [2,3 : 5,6‐{C4H8C(NAr)}2C5H3N]FeCl2 (Ar=1‐C10H7Fe1, 2‐Me‐1‐C10H6Fe2, 2‐(CHMePh)‐1‐C10H6Fe3, 2‐Cl‐1‐C10H6Fe4, 4‐Br‐1‐C10H6Fe5, 4‐NO2‐1‐C10H6Fe6), differing in the steric/electronic properties of the substituents appended to the N‐naphthalen‐1‐yl groups, have been synthesized in reasonable yield via a facile one‐pot route. The molecular structure of five‐coordinate Fe3 emphasizes the steric hindrance imposed on the iron center by the CHMePh‐substituted bicyclic aromatic groups. With either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO) as activator, the complexes displayed a wide range in catalytic activities for ethylene polymerization with the order for MMAO being: Fe3>Fe2≫Fe1>Fe4≫Fe5 while Fe6 was almost inactive. In particular, Fe3/MMAO exhibited exceptionally high activity at 70 °C (up to 15.7×106 g (PE) mol−1 (Fe) h−1) affording low molecular weight (2.97 kg mol−1) polyethylene of high linearity and narrow dispersity (Mw/Mn=1.38). Moreover, the same catalyst displayed excellent thermostability by maintaining high activity at 90 °C (up to 9.26×106 g (PE) mol−1 (Fe) h−1). Similar activity trends were observed with MAO though the catalysts were in general less active but formed distinctly higher molecular weight polyethylene. [ABSTRACT FROM AUTHOR]

Six types of ferrous chloride complex, [2‐(ArN=CMe)‐8‐(ArN)‐7,7‐Me2C9H6N]FeCl2 (Ar=2‐(C5H9)‐6‐MeC6H3Fe1, 2‐(C6H11)‐6‐MeC6H3Fe2, 2‐(C8H15)‐6‐MeC6H3Fe3, 2‐(C5H9)‐4,6‐Me2C6H2Fe4, 2‐(C6H11)‐4,6‐Me2C6H2Fe5, 2‐(C8H15)‐4,6‐Me2C6H2Fe6), each bearing a gem‐dimethyl‐substituted N,N,N‐chelating ligand that differs in the ortho‐cycloalkyl ring size and para‐substituent of the N‐aryl groups, are disclosed. All complexes have been prepared by a straightforward one‐flask route and characterized by FT‐IR spectroscopy and elemental analysis. In the case of Fe1, oxidation to form the oxo‐bridged diferric species [2‐(2‐(C5H9)‐6‐MeC6H3N=CMe)‐8‐(2‐(C5H9)‐6‐MeC6H3N)‐7,7‐Me2C9H6N]FeCl(μ‐O)FeCl3 (Fe1') has been demonstrated and its structural identity confirmed by single crystal X‐ray diffraction. Following treatment with either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), Fe1–Fe6 exhibited optimal catalytic activities at 60°C for ethylene polymerization [up to 2.35 × 107 g of PE (mol of Fe)−1 h−1 for Fe1/MMAO] producing linear polyethylene; even over prolonged run times, high activities were maintained. Moreover, this family of iron catalysts exhibited remarkable thermostability by displaying appreciable activity at temperatures as high as 100°C [activity up to 7.8 × 106 g of PE (mol of Fe)−1 h−1]. By varying the ring size of the ortho‐cycloalkyl and para‐R2 group (R2 = H, Me), excellent control over molecular weight of the polyethylenes could be achieved with values in the range 1.4–67.8 kg mol−1 obtainable. In addition, end‐group analysis of the polymers generated with Fe/MAO or Fe/MMAO revealed that both β‐H elimination and chain transfer to aluminum are competitive processes during chain termination. [ABSTRACT FROM AUTHOR]

Combined condensation and complexation of 2‐acetyl‐5,6,7‐trihydroquinolin‐8‐one, cobalt(II) chloride and the corresponding aniline has been employed as an effective one‐pot route to the 2‐(1‐(arylimino)ethyl)‐8‐arylimino‐5,6,7‐trihydroquinoline‐cobalt(II) chlorides (aryl=2‐Me‐4‐(CHPh2)‐6‐(C5H9)C6H2Co1, 2‐Me‐4‐(C5H9)‐6‐(CHPh2)C6H2Co2, 2‐(C5H9)‐4‐Me‐6‐(CHPh2)C6H2Co3, 2‐(C5H9)‐4,6‐(CHPh2)2C6H2Co4, 2‐(C6H11)‐4,6‐(CHPh2)2C6H2Co5, 2‐(C8H15)‐4,6‐(CHPh2)2C6H2Co6, 2‐F‐4,6‐(CHPh2)2C6H2Co7, 2‐Cl‐4,6‐(CHPh2)2C6H2Co8, 2‐Me‐4,6‐(CHPh2)2C6H2Co9). All complexes have been well characterized including by single crystal X‐ray diffraction for Co3. On activation with either MAO or MMAO, Co1 was the most active for ethylene polymerization with the MAO‐activated precatalyst reaching a peak level at 60 °C (up to 13.66×106 g (PE) mol−1(Co) h−1). By varying the electronic and steric properties of the ortho‐ and/or the para‐substituents of the N‐aryl groups, excellent control over molecular weight could be achieved with values falling in the range 0.97–101.63 kg mol−1 obtainable. Notably, with a benzhydryl group positioned on the ortho‐position of the N‐aryl group, a significant enhancement of the molecular weight was observed, while the least bulky ortho‐cyclopentyl substituent led to increased catalytic activity. As a final point, distinctive microstructural characteristics of the polyethylenes were observed with Co1/MAO producing near quantitative levels of vinyl end groups. [ABSTRACT FROM AUTHOR]

A one-pot template strategy has been utilized to synthesize sterically enhanced bis(imino)cyclohepta[b]pyridine-cobalt(II) chlorides, [2-{(Ar)N＝CMe}-9-{N(Ar)}C10H10N]CoCl2 (Ar = 2-(C5H9)-4,6-(CHPh2)2C6H2Co1, 2-(C6H11)-4,6-(CHPh2)2C6H2Co2, 2-(C8H15)-4,6-(CHPh2)2C6H2Co3, 2-(C12H23)-4,6-(CHPh2)2C6H2Co4, 2,6-(C5H9)2-4-(CHPh2)C6H2Co5). All five complexes have been characterized by a combination of FT-IR spectroscopy, elemental analysis and single crystal X-ray diffraction. The molecular structures of Co1, Co3 and Co5 highlight the substantial steric hindrance imparted by the 2-cycloalkyl-6-benzhydryl or 2,6-dicyclopentyl ortho-substitution pattern; distorted square pyramidal geometries are exhibited in each case. On activation with methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), all the complexes (apart from Co4/MAO) were active ethylene polymerization catalysts (up to 3.70 × 106 g PE per mol (Co) per h for Co5/MMAO), operating effectively at temperatures between 50 °C and 60 °C, producing polyethylenes with high molecular weights (up to 589.5 kg mol−1 for Co3/MAO). Furthermore, all polymers were highly linear (Tm > 130 °C) with narrow dispersities (Mw/Mn range: 2.0–3.0). The coexistence of two chain termination pathways, β-H elimination and transfer to aluminum, has been demonstrated using 13C/1H NMR spectroscopy. [ABSTRACT FROM AUTHOR]

Five distinct α,α′-bis(arylimino)-2,3:5,6-bis(hexamethylene)pyridine-cobalt(II) chloride complexes, [2,3:5,6-{C5H10C(NAr)}2C5HN]CoCl2 (Ar = 2,6-Me2C6H3, Co1; 2,6-Et2C6H3, Co2; 2,6-i-Pr2C6H3, Co3; 2,4,6-Me3C6H2, Co4; 2,6-Et2-4-MeC6H2, Co5), have been synthesized by one-pot template reaction of α,α′-dioxo-2,3:5,6-bis(hexamethylene)pyridine with the corresponding aniline and cobalt(II) chloride in acetic acid. The molecular structures of Co2 and Co3 reveal distorted square pyramidal geometries with two conformationally flexible eight-membered rings, a feature of the ligand manifold. On activation with either methylaluminoxane (MAO) or modified MAO (MMAO), all five complexes displayed high catalytic activities for ethylene polymerization (up to 3.62 × 106 g PE mol-1 (Co) h-1) generating strictly linear polyethylenes with the activity decreasing in the orders: Co4 > Co5 > Co1 > Co2 > Co3 (MAO) and Co1 > Co4 > Co2 > Co5 > Co3 (MMAO). Moreover, the nature of the aluminoxane cocatalyst employed had a marked effect on the molecular weight and distribution (Mw/Mn) of the polymeric material obtained. For example using MAO, high molecular weight polyethylene (Mw ≈ 105 g mol-1) with a narrow monomodal molecular weight distribution (2.1-3.6) was a characteristic, while using MMAO, the polyethylene was of lower molecular weight (Mw ≈ 104 g mol-1) and exhibited a mono- to bimodal distribution (10.1-23.8) depending on the ratio of MMAO employed, temperature, and run time. [ABSTRACT FROM AUTHOR]

ABSTRACT The N,N-diaryliminoacenaphthenes, 1,2-[2,4-{(4-FC6H4)2CH}2-6-MeC6H4N]2-C2C10H6 ( L1) and 1-[2,4-{(4-FC6H4)2CH}2-6-MeC6H4N]-2-(ArN)C2C10H6 (Ar = 2,6-Me2C6H3 L2, 2,6-Et2C6H3 L3, 2,6- i-Pr2C6H3 L4, 2,4,6-Me3C6H2 L5, 2,6-Et2-4-MeC6H2 L6), incorporating at least one N−2,4-bis(difluoro benzhydryl)-6-methylphenyl group, have been synthesized and fully characterized. Interaction of L1- L6 with (DME)NiBr2 (DME = 1,2-dimethoxyethane) generates the corresponding nickel(II) bromide N,N-chelates, LNiBr2 ( 1- 6), in high yield. The molecular structures of 3 and 6 reveal distorted tetrahedral geometries at nickel with the ortho-substituted difluorobenzhydryl group providing enhanced steric protection to only one side of the metal center. On activation with various aluminum alkyl co-catalysts, such as methylaluminoxane (MAO) or Et2AlCl, 1- 6 displayed outstanding activity toward ethylene polymerization (up to 1.02 × 107 g of PE (mol of Ni)−1 h−1). Notably 1, bearing equivalent fluorobenzhydryl-substituted N-aryl groups, was able in the presence of Et2AlCl to couple high activity with exceptional thermal stability generating high molecular weight branched polyethylenes at temperatures as high as 100 °C. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 1971-1983 [ABSTRACT FROM AUTHOR]

Five novel air- and moisture-stable polymetallic Ti and Zr amino acid-derived amine bis(phenolate) (ABP) complexes were synthesised and fully characterised, including X-ray crystallographic studies. The reaction of the ABP proligands with Ti or Zr alkoxides has resulted in the formation of polymetallic aggregates of different nuclearity. The steric bulk on the pendant arm of the ligand was found to play a critical role in establishing the nuclearity of the aggregated complex. Sterically, less-demanding groups, such as H or Me, facilitated the formation of tetrametallic Ti clusters, bridged by carboxylate groups, while increased steric bulk (tBu) led to the formation of binuclear μ-oxo-bridged species. The isolated complexes were employed as catalysts for the ring opening polymerisation (ROP) of rac-lactide. Overall, the Ti catalysts were all active with the smaller, bimetallic Ti aggregates exhibiting relatively faster rates. A monometallic, bis(ABP) Zr complex was found to exert remarkable ROP activity, albeit with limited control over the tacticity and molecular weight distribution of the polymer. A further oxo-bridged Zr cluster was shown to display a previously unprecedented trimetallic structure and achieved a moderate rate in the ROP of rac-lactide. [ABSTRACT FROM AUTHOR]

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: Fe1C5H9/CHPh2~Fe5C5H9/C5H9 > Fe2C6H11/CHPh2 > Fe3C8H15/CHPh2 > Fe4C12H23/CHPh2. Furthermore, strictly linear polyethylenes (Tm > 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 (Mw/Mn range: 2.3–4.7), highlighting the well-controlled nature of these polymerizations. [ABSTRACT FROM AUTHOR]

The bis(arylimino)pyridines, 2‐[CMeN{2,6‐{(4‐FC6H4)2CH}2–4‐NO2}]‐6‐(CMeNAr)C5H3N (Ar = 2,6‐Me2C6H3L1, 2,6‐Et2C6H3L2, 2,6‐i‐Pr2C6H3L3, 2,4,6‐Me3C6H2L4, 2,6‐Et2–4‐MeC6H2L5), each containing one N′‐2,6‐bis{di(4‐fluorophenyl)methyl}‐4‐nitrophenyl group, have been synthesized by two successive condensation reactions from 2,6‐diacetylpyridine. Their subsequent treatment with anhydrous cobalt (II) chloride gave the corresponding N,N,N′‐CoCl2 chelates, Co1 – Co5, in excellent yield. All five complexes have been characterized by 1H/19F NMR and IR spectroscopy as well as by elemental analysis. In addition, the molecular structures of Co1 and Co3 have been determined and help to emphasize the differences in steric properties imposed by the inequivalent N‐aryl groups; distorted square pyramidal geometries are adopted by each complex. Upon activation with either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), precatalyts Co1 – Co5 collectively exhibited very high activities for ethylene polymerization with 2,6‐dimethyl‐substituted Co1 the most active (up to 1.1 × 107 g (PE) mol−1 (Co) h−1); the MAO systems were generally more productive. Linear polyethylenes of exceptionally high molecular weight (Mw up to 1.3 × 106 g mol−1) were obtained in all cases with the range in dispersities exhibited using MAO as co‐catalyst noticeably narrower than with MMAO [Mw/Mn: 3.55–4.77 (Co1 – Co5/MAO) vs. 2.85–12.85 (Co1 – Co5/MMAO)]. Significantly, the molecular weights of the polymers generated using this class of cobalt catalyst are higher than any literature values reported to date using related N,N,N‐bis (arylimino)pyridine‐cobalt catalysts. [ABSTRACT FROM AUTHOR]

Five examples of unsymmetrical 1,2‐bis (arylimino) acenaphthene (L1 – L5), each containing one N‐2,4‐bis (dibenzocycloheptyl)‐6‐methylphenyl group and one sterically and electronically variable N‐aryl group, have been used to prepare the N,N′‐nickel (II) halide complexes, [1‐[2,4‐{(C15H13}2–6‐MeC6H2N]‐2‐(ArN)C2C10H6]NiX2 (X = Br: Ar = 2,6‐Me2C6H3Ni1, 2,6‐Et2C6H3Ni2, 2,6‐i‐Pr2C6H3Ni3, 2,4,6‐Me3C6H2Ni4, 2,6‐Et2–4‐MeC6H2Ni5) and (X = Cl: Ar = 2,6‐Me2C6H3Ni6, 2,6‐Et2C6H3Ni7, 2,6‐i‐Pr2C6H3Ni8, 2,4,6‐Me3C6H2Ni9, 2,6‐Et2–4‐MeC6H2Ni10), in high yield. The molecular structures Ni3 and Ni7 highlight the extensive steric protection imparted by the ortho‐dibenzocycloheptyl group and the distorted tetrahedral geometry conferred to the nickel center. On activation with either Et2AlCl or MAO, Ni1 – Ni10 exhibited very high activities for ethylene polymerization with the least bulky Ni1 the most active (up to 1.06 × 107 g PE mol−1(Ni) h−1 with MAO). Notably, these sterically bulky catalysts have a propensity towards generating very high molecular weight polyethylene with moderate levels of branching and narrow dispersities with the most hindered Ni3 and Ni8 affording ultra‐high molecular weight material (up to 1.5 × 106 g mol−1). Indeed, both the activity and molecular weights of the resulting polyethylene are among the highest to be reported for this class of unsymmetrical 1,2‐bis (imino)acenaphthene‐nickel catalyst. [ABSTRACT FROM AUTHOR]

This review surveys more recent literature concerning N -ligated group 4 metal ethylene polymerization catalysts and in particular how modulation of their structural properties can influence not only catalytic performance and temperature stability but also the intrinsic properties of the polyethylenes. • Diversity of N -ligated group IV (Ti, Zr, Hf) metal complexes accessible. • Control of activity and thermal stability of catalysts through N -ligand modification. • Correlations between the active species and the microstructure of the polyethylene. • High molecular weight or even ultra-high molecular weight polyethylene achievable. • Controlled incorporation of co-monomer in ethylene/1-hexene copolymerizations. Group 4 metal (Zr, Ti, Hf) catalysts for olefin polymerization and specifically those based on non-metallocene complexes have continued to be a subject of intense study in homogeneous catalysis. With a view to forming new or improved polyolefinic materials, complexes bearing N -donor anionic ligands such as β - diketiminate, amidinate, guanidinate, amido, imido as well as mixed N -donor ligands including N,C,C -azaallyl and N,O -phenoxy-imine, have been central to many key developments; high catalytic activities for homo- and copolymerization of ethylene have been a highlight of their catalysis. The fine tuning of these nitrogen-containing ligands significantly controls the catalytic performances of their metal catalysts as well as the structural properties of the resulting polymers with high molecular weight or even ultra-high molecular weight materials accessible. In this review the focus is on more recent publications in the field, in which we correlate the influence of ligand structure with the catalytic performance and microstructure of the polyethylenes. Furthermore, we examine the effects of co-catalyst on activity and thermostability of the precatalyst while efforts directed towards the copolymerization of ethylene with 1-hexene are also summarized. Overall, this work presents an overview of current knowledge pertaining to catalyst design and especially with regard to how the modulation of steric and electronic properties impact on the (co)polymerization process. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Straightforward and cost-effective process to produce elastomeric polyethylene. • Highly branched polyethylenes by bis(imino)acenaphthene-nickel(II) catalysts. • Highly active catalysts for the polymerization of ethylene. • Access to branched polyethylenes with narrow polydispersity. • Polyethylenes with good tensile strength and elastic recovery. Abstract The 4,4′-difluorobenzhydryl-containing nickel(II) bromide and chloride chelates, [1-[2,6-{(4-F-C 6 H 4) 2 CH} 2 -4-{C(CH 3) 3 }-C 6 H 2 N]-2-(ArN)C 2 C 10 H 6 ]NiX 2 (X = Br: Ar = 2,6-Me 2 C 6 H 3 Ni1 , 2,6-Et 2 C 6 H 3 Ni2 , 2,6- i -Pr 2 C 6 H 3 Ni3 , 2,4,6-Me 3 C 6 H 2 Ni4 , 2,6-Et 2 -4-MeC 6 H 2 Ni5 and X = Cl: Ar = 2,6-Me 2 C 6 H 3 Ni6 , 2,6-Et 2 C 6 H 3 Ni7 , 2,6- i -Pr 2 C 6 H 3 Ni8 , 2,4,6-Me 3 C 6 H 2 Ni9 , 2,6-Et 2 -4-MeC 6 H 2 Ni10), have been prepared and fully characterized. The solid-state structures of representative Ni3 and Ni7 display distorted tetrahedral geometries which are maintained in solution with broad paramagnetically shifted resonances a feature of all the 1H and 19F NMR spectra; the effect the halide (Br/Cl) ligand has on the proton and fluorine chemical shifts presents a further point of interest. All ten nickel complexes displayed, on activation with either MAO (methylaluminoxane) or EASC (ethyl aluminum sesquichloride), very high activities (up to 1.36 × 107 g PE mol−1 (Ni) h−1) for ethylene polymerization at either 1 or 10 atm C 2 H 4 with the structural features of the N,N' -ligand influential. Significantly, with EASC as co-catalyst, Ni5 was capable of operating effectively at 90 °C without comprising too much catalytic activity [ ca. 4.34 × 106 g PE mol−1 (Ni) h−1]. All the polyethylenes are highly branched with the branching content and type of branch strongly affected by a combination of temperature, pressure and the class of co-catalyst employed. Moreover, good tensile strength (ε b up to 2839.5%) and elastic recovery (up to 74%) have been displayed, properties that are characteristic of thermoplastic elastomers (TPEs). [ABSTRACT FROM AUTHOR]

• 2,6-Dibenzhydryl-4-trifluoromethoxy modified bis(imino)pyridylferrous chlorides. • Highly active in ethylene polymerization up to 18.4 × 106 g (PE) mol-1 (Fe) h-1. • Highly linear polyethylenes with a wide range of molecular weights. • Full measurements of ligands compounds and complexes. The capacity to broaden the range of molecular weights displayed by polyolefinic materials is an important factor to be considered in the design of polymerization catalysts. Herein, the 2,6-dibenzhydryl-4-trifluoromethoxy modified bis(imino)pyridyl-ferrous chlorides, [2-[CMeN{2,6-{(C 6 H 5) 2 CH} 2 -4-(F 3 CO)C 6 H 2 }]-6-(CMeNAr)C 5 H 3 N]FeCl 2 [Ar = 2,6-Me 2 C 6 H 3 Fe1 , 2,6-Et 2 C 6 H 3 Fe2 , 2,6- i -Pr 2 C 6 H 3 Fe3 , 2,4,6-Me 3 C 6 H 2 Fe4 , 2,6-Et 2 -4-MeC 6 H 2 Fe5 ], are used as precatalysts in the solution polymerization of ethylene. On the activation with either MAO or MMAO, all complexes displayed high productivity [up to 18.4 × 106 g (PE) mol-1 (Fe) h-1 for Fe5 /MAO], generating highly linear polyethylenes with a wide range of molecular weights (M w range: 0.85 × 103 to 8.80 × 105 g mol-1). Notably, higher activity was achieved in hexane than in toluene under MAO activation, while the opposite trend was seen with MMAO, highlighting the key role played by solvent in the polymerization process. By comparison with structurally related iron catalysts, the presence of the electron withdrawing para -trifluoromethoxy group has the effect of increasing the molecular weight of the polyethylene. In addition to the polymerization studies, full synthetic and characterization details are presented for Fe1 - Fe5 including the X-ray structures of Fe1 and Fe2. The iron precatalysts containing trifluoromethoxy group, when activated with MAO or MMAO, proved highly active toward ethylene polymerization producing highly linear polyethylenes with a wide range of molecular weights. The solvent effect of toluene or hexane on catalytic activity and polymer properties was also invest [Display omitted] [ABSTRACT FROM AUTHOR]

A set of six 2-iminopyridine-nickel(II) complexes, [2-{C(Me)=NAr}C 5 H 4 N]NiCl 2 (Ar = 1-C 10 H 7 Ni1 , 2-Me-1-C 10 H 6 Ni2 , 2-(CHMePh)-1-C 10 H 6 Ni3 , 4-(NNC 6 H 5)-1-C 10 H 6 Ni4 , 4-(NNC 6 H 4 -4-Me)-1-C 10 H 6 Ni5 , 4-(NNC 6 H 4 -4-F)-1-C 10 H 6 Ni6), all N -functionalized with naphthalen-1-yl or its substituted alkyl or aryldiazenyl derivatives, have been readily synthesized from their corresponding free N,N -ligand, L1 – L6. On crystallization of Ni3 , the chloride-bridged trimetallic species, [(L3) 3 Ni 3 Cl 6 (OH 2)], was identified as an aqua adduct by single crystal X-ray diffraction. When activated with either MAO or MMAO, high catalytic activity for ethylene polymerization was achieved using Ni1 – Ni6 (up to 10.1 × 106 g (PE) mol−1 h−1 for Ni3 /MAO), affording low molecular weight polyethylene (M w range: 0.81–3.50 kg mol−1) with low melting temperature and narrow dispersity. 13C NMR spectroscopic analyses of these polyethylenic waxes revealed the formation of branched macromolecules with branching densities up to 69 per 1000 carbons. Further analysis revealed these polymers to contain predominantly methyl branches (%Me range: 7.8–9.0), with lower levels of longer chain branching and some branch-on branch structure (% sec -Bu range: 0.07–0.12%). Moreover, their 1H and 13C NMR spectra showed various levels of unsaturated functionality in the form of terminal and internal olefins. The 2-(naphthylen-1-yl)iminopyridines were modified with different substituents for their chloro-bridged dinickel complexes, which performed high activities toward ethylene polymerization with forming highly branched unsaturated PE waxes with narrow dispersity. [Display omitted] • Nickel complexes catalyze the polymerization of ethylene with high activity. • Highly branched unsaturated PE waxes are accessible. • The PE generated displays a narrow molecular weight distribution (range: 1.53–2.29). • The mass and molecular weight of the polymer are linearly related to the polymerization time. [ABSTRACT FROM AUTHOR]

Six structurally related bis(arylimino)trihydroquinolyl-cobalt (II) chloride complexes [2-(ArN CCH 3)-8-(ArN)-5,6,7-C 9 H 8 N]CoCl 2 (Ar = 2-(C 5 H 9)-6-MeC 6 H 3 Co1 , 2-(C 6 H 11)-6-MeC 6 H 3 Co2 , 2-(C 8 H 15)-6-MeC 6 H 3 Co3 , 2-(C 5 H 9)-4,6-Me 2 C 6 H 2 Co4 , 2-(C 6 H 11)-4,6-Me 2 C 6 H 2 Co5 , 2-(C 8 H 15)-4,6-Me 2 C 6 H 2 Co6), distinguishable by the ring size of the ortho -cycloalkyl substituent and type of para -R group, have been synthesized and characterized. A distorted square pyramidal geometry is a feature of the molecular structure of Co4 with the two ortho -cyclopentyl groups located on neighboring N -aryl groups trans -configured. Compounds Co1 – Co6 , on activation with methylaluminoxane (MAO) or modified MAO (MMAO), proved highly productive catalysts for ethylene polymerization at 60 °C [up to 17.1 × 106 g (PE) mol−1(Co) h−1 for cyclopentyl-containing Co4 /MAO]; even at 90 °C significant activity was attainable (up to 6.75 × 106 g (PE) mol−1(Co) h−1). Strictly linear polyethylene waxes of low molecular weight (ca. 1.50 kg mol−1), narrow dispersity (M w / M n range: 1.1–2.4) and incorporating high levels of vinyl end-groups were generated. Post-functionalization of these PE waxes by epoxidation, thiol-ene addition and cross-olefin metathesis to form e-PE, PE-S-CH 2 CH 2 NH 2 ·HCl and PE-MMA, respectively, has been demonstrated. For comparative purposes, [2-(ArN CCH 3)-8-ArN-5,6,7-C 9 H 8 N]CoCl 2 (Ar = 2,4,6-Me 3 C 6 H 2 Co o -Me , 2-(Ph 2 CH)-4,6-Me 2 C 6 H 2 Co o -CHPh2) have also been prepared and evaluated as polymerization catalysts. Image 1 • Cobalt ethylene polymerization catalysts capable of running at temperatures up to 90 °C. • ortho -Cycloalkyl ring-size variation allows fine control of catalytic performance. • PE waxes with narrow dispersities and high levels of vinyl end-groups are produced. • Amenability of the PE waxes to post-functionalization by epoxidation, thiol-ene addition and cross-olefin metathesis has been demonstrated. • Ready synthesis of catalysts and characteristic vinyl-polyethylenes offer industrial potential. [ABSTRACT FROM AUTHOR]

Potassium benzimidates have been shown to efficiently initiate the ROP of ε-CL and L -LA to form linear polyesters capped with methoxy groups. By contrast, in the presence of BnOH, ROP of ε-CL afforded PCL capped with a BnO group as the major component, while ROP of L -LA gave CH 3 O-capped PLLA as the major species. [Display omitted] • Novel potassium N -arylbenzimidates that are readily prepared with a non-toxic metal center. • Unusual two-dimensional polymeric structures adopted. • High efficiency as catalysts for the ROP of the cyclic esters, ε-CL and L -LA. • Linear PCL or PLLA accessible with the end-group composition affected by the quenching solvent as well as BnOH. • Mechanistic insight into the pathways followed by potassium-mediated ROP catalysis. Eight examples of potassium N -arylbenzimidates, [K 2 {OCPhN(2-R1,6-R2,4-R3C 6 H 2)} 2 ] n (R1 = R2 = R3 = H K1 ; R1 = R2 = H, R3 = Me K2 ; R1 = R2 = H, R3 = OMe K3 ; R1 = R2 = H, R3 = F K4 ; R1 = R2 = H, R3 = Cl K5 ; R1 = R2 = H, R3 = NO 2 K6 ; R1 = R3 = H, R2 = Me K7 ; R1 = R2 = Me, R3 = H K8), have been prepared and characterized by spectroscopic and analytical techniques. In addition, the molecular structures of K6 (3THF) and K7 were determined and shown to consist of two-dimensional coordination polymers involving combinations of π-aryl and NO 2 -/N-donor interactions. In the presence of benzyl alcohol (BnOH), K1 - K8 all showed high efficiency for the ROP of ε -caprolactone (ε -CL) and L -lactide (L -LA), affording linear polyesters (PCL and PLA) with BnO or CH 3 O end-groups (the latter derived from the quenching solvent). By contrast, lower conversions were achievable when the runs were performed in the absence of BnOH. Mechanistic studies have indicated that for runs performed with BnOH, monomer activation by benzyl alkoxide and N -arylbenzimidate were competitive pathways for the ROP of both cyclic esters. Furthermore, the nature of the N -aryl substituents influenced the ROP of ε -CL and L -LA in distinct ways. For example, K1 and K6 showed lower conversions of ε -CL than that observed for K2 - K5 , K7 and K8 , while the conversions of L -LA using K1 - K3 and K6 exceeded that shown by K4 , K5 , K7 and K8. In addition, the type of solvent greatly affected their catalytic efficiency with hexane and toluene proving superior to THF and CH 2 Cl 2 in the ROP of ε -CL. Conversely, for L -LA almost quantitative conversions were observed in THF, CH 2 Cl 2 and toluene while hexane was less effective. Furthermore, kinetic studies of the ROP of L -LA performed at different run temperatures highlighted the beneficial effect of higher temperature. [ABSTRACT FROM AUTHOR]