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Based on iminopyridine ligands (L1–L3), Fe(II) (Fe1–Fe3) and Co(II) (Co1–Co3) complexes were synthesized and characterized well. According to single-crystal XRD studies, Co3 exhibits a dimeric structure with a four-coordinated metal center. Whereas, the iron complexes (Fe1 and Fe3) coordinate with two ligands to form a distorted-octahedral and distorted-trigonal bipyramidal geometry, respectively. All these catalysts were tested for the polymerization of isoprene. Using MAO as the co-catalyst, the Fe3 catalyst containing a bulky substituent can provide trans-1,4-unit (64%) polyisoprenes, while the Fe1 catalyst afforded trans-1,4-unit polyisoprenes (32%). Conversely, the combination of EASC as the co-catalyst with Fe1–Fe3 catalysts can give 1,4-unit polyisoprenes with high trans-1,4-unit selectivity (up to 88%). The central metal atom of the catalysts plays a crucial role in isoprene polymerization and significantly affects their activity. Fe(II) catalysts showed the highest activity (up to 99% yield), and afforded polyisoprenes with high molecular weights (191 kg mol−1). However, Co(II) systems exhibited lower activity (60% yield) and the obtained polyisoprenes were of lower molecular weights (2.15 kg mol−1) with broad molecular weight distribution. [ABSTRACT FROM AUTHOR]

Six examples of α,α′-bis(arylimino)-2,3:5,6-bis(pentamethylene)pyridine-cobalt(II) chlorides, [2,3:5,6-{C 4 H 8 C(NAr)} 2 C 5 HN]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 ), containing N-aryl groups that differ in either the ring size of the ortho -cycloalkyl substituents or the para -R group (R = H, Me), have been synthesized using a one-pot template approach. The molecular structure of Co1 highlights the ring puckering of both the ortho -cyclopentyl substituents and the two pyridine-fused seven-membered rings; a square-based pyramidal geometry is conferred about the metal center. On activation with either methylaluminoxane (MAO) or modified MAO (MMAO), all six complexes afforded strictly linear polyethylene (all T m 's > 130 °C) with high molecular weight ( M w up to 64.3 kg mol −1 ). Furthermore, all precatalysts displayed high activities (up to 2 × 10 6  g PE mol -1 (Co) h −1 ) at temperatures between 20 and 60 °C with the catalytic activities correlating with the type of ortho -cycloalkyl substituent: cyclohexyl ( Co2 , Co5 ) > cyclopentyl ( Co1 , Co4 ) > cyclooctyl ( Co6 , Co3 ) for either R = H or Me. The narrow unimodal distributions of the resulting polymers are consistent with single-site active species for the catalysts. [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]

Graphical abstract Highlights • Bis(imino)-2,3:5,6-bis(pentamethylene)pyridines and their cobalt complexes. • Highly active precatalysts for ethylene polymerization. • Linear polyethylenes with narrow dispersities and vinyl end-groups. • Modulation of molecular weight through ortho -benzhydryl substitution. Abstract The cycloheptyl-fused cobalt(II) chloride complexes, [2,3:5,6-{C 4 H 8 C(N(2-R1-4-R2-6-(CHPh 2)C 6 H 2))} 2 C 5 HN]CoCl 2 (R1 = R2 = Me Co1 , R1 = Me, R2 = CHPh 2 Co2 , R1 = Et, R2 = CHPh 2 Co3 , R1 = i -Pr, R2 = CHPh 2 Co4 , R1 = Cl, R2 = CHPh 2 Co5 , R1 = CHPh 2 , R2 = i -Pr Co6 , R1 = CHPh 2 , R2 = t -Bu Co7 , R1 = CHPh 2 , R2 = F Co8), have been prepared by a one-pot template approach. The molecular structures of Co1 , Co6 and Co8 highlight the varying degrees of steric protection of the metal center imposed by the ortho -benzhydryl/-R1 group pairing. On activation with either MAO or MMAO, Co1–Co5 collectively displayed high activity (up to 2.87 × 106 g (PE) mol−1 (Co) h−1 at 40 °C) affording highly linear low molecular weight polyethylene (M w range: 12.8–59.4 kg mol−1) with narrow polydispersities (M w / M n range: 1.4–2.7). End-group analysis of the polymers highlights the importance of both β-H elimination and chain transfer to aluminum as termination pathways. In relative terms, MMAO proved a marginally more effective activator than MAO with the catalytic activity, in either case, falling in the order: Co1 > Co5 > Co2 > Co3 > Co4. In marked contrast, the 2,6-(CHPh 2) 2 -substituted precatalysts, Co6 , Co7 and Co8 gave, in the presence of the same aluminoxane activators, only trace amounts of polyethylene. [ABSTRACT FROM AUTHOR]

Treatment of AlMe 3 with bidentate N, O-ligands, HOC(Me)(Ph)C 6 H 4 –NMe 2 -2 ( L 1 H) or HOC(CH 2 ) 5 C 6 H 4 –NMe 2 -2 ( L 2 H) in different molar ratios, four novel aluminum complexes ( 1 ), ( 2 ), ( 3 ) and ( 4 ) were obtained in good yield. Complexes 1 – 4 were characterized by 1 H and 13 C NMR spectroscopy, elemental analyses and single crystal X-ray diffraction techniques. Each of the complexes 1 , 2 , 3 and 4 was tested for the capable of catalyzed Meerwein–Ponndorf–Verley (MPV) reduction of ketones or aldehydes with low catalyst loadings under mild conditions and showed good to excellent catalytic activities. [ABSTRACT FROM AUTHOR]

Five examples of hither-to-unknown ferrous chloride precatalysts have been prepared for ethylene polymerization. The impact of steric/electronic effect and polymerization reaction parameters on the catalytic performance, thermal stability with MAO or MMAO and the microstructure of the polyethylene are investigated in detail. [Display omitted] • Novel iron(II) complexes bearing sterically hindered dibenzocycloheptyl group were synthesized. • Higher activity towards ethylene polymerization. • Enhanced thermal stability. • Vinyl end polyethylene via modified bis(arylimino)pyridine-ferrous chloride precatalyst. Unsymmetrical Fe(II) complexes bearing tridentate NNN- bis(arylimino)pyridine ligand of the general formula [2-(2,4-bis(C 15 H 13) 2 -6-CH 3 C 6 H 2 N)-6-(ArN)C 9 H 9 N]FeCl 2 {Ar = 2,6-(CH 3) 2 C 6 H 3 (Fe1), 2,6-(C 2 H 5) 2 C 6 H 3 (Fe2), 2,6-(C 3 H 7) 2 C 6 H 3 (Fe3), 2,4,6-(CH 3) 3 C 6 H 2 (Fe4) and 2,6-(C 2 H 7) 2 -4-CH 3 C 6 H 2 (Fe5)} have been prepared in good yields. All the complexes were characterized by FT-IR spectroscopy, elemental analysis, and single-crystal X-ray diffraction analysis for Fe2 and Fe3. Upon activation with MAO or modified-MAO, all the complexes displayed high activity at elevated temperature with peak performance up to 2.13 × 107 g PE (mol of Fe)−1 h-1 using Fe4 at 70 °C in combination with modified-MAO. The most sterically hindered precatalyst Fe3 produced high molecular-weight polyethylene up to 307.12 kg mol-1 at 70 °C with MAO as co-catalyst. Particularly, polyethylene of vinyl end functionality was obtained with MAO. Significantly, this developed catalytic system maintained the good catalytic performance of 9.67–7.59 × 106 g PE (mol of Fe)−1 h-1 and 1.51–1.09 × 107 g PE (mol of Fe)−1 h-1 using Fe1 with MAO or modified-MAO at 80 °C–90 °C, respectively. Notably, the activity of 3.12 or 2.76 × 106 g PE (mol of Fe)−1 h-1 was achieved even at 100 °C; indicating high thermal stability of the active species. Indeed, the thermal stability and molecular weight of the resultant polyethylene reached the highest values to be reported for this class of unsymmetrical 2,6-bis(arylimino)pyridine-ferrous precatalysts. [ABSTRACT FROM AUTHOR]