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Inspired by the cooperative multi-metallic activation in metalloenzyme catalysis, artificial enzymes as multi-metallic catalysts have been developed for improved kinetics and higher selectivity. Previous models about multi-metallic catalysts, such as cross-linked polymer-supported catalysts, failed to precisely control the number and location of their active sites, leading to low activity and selectivity. In recent years, metallopolymers with metals in the sidechain, also named as sidechain metallopolymers (SMPs), have attracted much attention because of their combination of the catalytic, magnetic, and electronic properties of metals with desirable mechanical and processing properties of polymeric backbones. Living and controlled polymerization techniques provide access to SMPs with precisely controlled structures, for example, controlled degree of polymerization (DP) and molecular weight dispersity (Đ), which may have excellent performance as multi-metallic catalysts in a variety of catalytic reactions. This review will cover the recent advances about SMPs, especially on their synthesis and application in catalysis. These tailor-made SMPs with metallic catalytic centers can precisely control the number and location of their active sites, exhibiting high catalytic efficiency. [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]

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]

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]