Studies of electronic effects of modified pyridine-imine ligands utilized in cobalt-catalyzed meta-selective Diels–Alder reactions

Hilt, Gerhard; Janikowski, Judith; Schwarzer, Martin C.; Burghaus, Olaf; Sakow, Dimitri; Bröring, Martin; Drüschler, Marcel; Huber, Benedikt; Roling, Bernhard; Harms, Klaus; Frenking, Gernot

doi:10.1016/j.jorganchem.2013.09.020

Cited by 14 publications

(12 citation statements)

References 40 publications

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“…The results of this investigation pointed strongly towards steric factors being responsible for the dramatic change in regioselectivities . Recently, Frenking also showed that electronic modifications in the 4 and 4′ positions of the pyridine‐imine ligands (R 1 and R 2 , Scheme ) had negligible effect on the regioselectivities . These calculations were in very good agreement with the experiments, so further optimisation of the catalyst system to increase the regioselectivity will have to focus on steric rather than electronic modifications.…”

Section: Methodssupporting

confidence: 77%

1,4‐Cyclohexadienes—Easy Access to a Versatile Building Block via Transition‐Metal‐Catalysed Diels–Alder Reactions

Hilt

2014

The Chemical Record

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1,4-Cyclohexadiene derivatives are easily accessed via transition-metal cycloadditions of 1,3-dienes with alkynes. The mild reaction conditions of several transition-metal-catalysed reactions allows the incorporation of various functional groups to access functionalised 1,4-cyclohexadienes. The control of the regiochemistry in the intermolecular cobalt-catalysed Diels-Alder reaction is realised utilising different ligand designs. The functionalised 1,4-cyclohexadiene derivatives are valuable building blocks in follow-up transformations. Finally, the oxidation of the 1,4-cyclohexadienes can be accomplished under mild conditions to generate the corresponding arene derivatives.

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Section: Methodssupporting

confidence: 77%

1,4‐Cyclohexadienes—Easy Access to a Versatile Building Block via Transition‐Metal‐Catalysed Diels–Alder Reactions

Hilt

2014

The Chemical Record

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“…The desired compounds were purified through recrystallization in hexane ( L1 , L3 ), reduced pressure distillation ( L4 ) or column chromatography ( L2 , L5 ). Ligands L1 , L2 , L4 , and L5 were confirmed according to the references [29,30,31,32,33] and novel ligand L3 was characterized by 1 H NMR, 13 C NMR, 19 F NMR, and HRMS-ESI (See Supplementary Materials, Figures S1–S4).…”

Section: Resultsmentioning

confidence: 99%

“…Isoprene was purchased from Aladdin Industrial Corporation (Shanghai, China), dried over CaH 2 and distilled prior to use. 1-(pyridin-2-yl)- N -(4-(trifluoromethyl)phenyl)methanimine ( L1 ), ( E )- N -(2,6-difluorophenyl)-1-(pyridin-2-yl)methanimine ( L2 ), ( E )-2,4,4-Trimethyl- N -(pyridin-2-ylmethylene)pentan-2-amine ( L4 ) and 1-(pyridin-2-yl)- N -(2,4,6-(triphenyl)phenyl)methanimine ( L5 ) are not commercially available and can be prepared using reported procedure [29,30,31,32,33]. Complexes 4a (C 14 H 22 Cl 2 FeN 2 ), 5a (C 60 H 44 Cl 4 Fe 2 N 4 ) and 4b (C 14 H 22 Cl 2 CoN 2 ), 5b (C 30 H 22 Cl 2 CoN 2 ) were synthesized using reported routes [27,28].…”

Section: Methodsmentioning

confidence: 99%

Influences of Fluorine Substituents on Iminopyridine Fe(II)- and Co(II)-Catalyzed Isoprene Polymerization

et al. 2018

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A series of iminopyridine complexes of Fe(II) and Co(II) complexes bearing fluorinated aryl substituents were synthesized for the polymerization of isoprene. The structures of complexes 3a, 2b and 3b were determined by X-ray diffraction analysis. Complex 3a contained two iminopyridine ligands coordinated to the iron metal center forming an octahedral geometry, whereas 2b adopted a chloro-bridged dimer, and 3b featured with two patterns of cobalt centers bridged via chlorine atoms. Complexes 2b and 3b represented rare examples of chlorine bridged bimetallic Co(II) complexes. The fluorine substituents effects, particularly on catalytic activity and polymer properties such as molecular weight and regio-/stereo-selectivity were investigated when these complexes were employed for isoprene polymerization. Among the Fe(II)/methylaluminoxane (MAO) systems, the 4-CF3 substituted iminopyridine Fe(II) complex 1a was found as a highly active isoprene polymerization catalyst exhibiting the highest activity of 106 g·(mol of Fe)−1·h−1. The resultant polymer displayed lower molecular weight (Mn = 3.5 × 104 g/mol) and moderate polydispersity index (PDI = 2.1). Furthermore, the ratio of cis-1,4-/3,4 was not affected by the F substituents. In the series of Co(II)/AlEt2Cl binary systems, complexes containing electron-withdrawing N-aryl substituents (R = 4-CF3, 2,6-2F) afforded higher molecular weights polyisoprene than that was obtained by the complex containing electron-donating N-alkyl substituents (R = octyl). However, ternary components system, complex/MAO/[Ph3C][B(C6F5)4] resulted in low molecular weight polyisoprene (Mn < 2000) with high trans-1,4-unit (>95%).

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“…All solvents were distilled from appropriate drying agents under an atmosphere of nitrogen prior to use. Ligand precursors [C 5 H 4 N‐2‐C(H) = N‐C 6 H 4 ‐R] [R = H ( 1 ); CH 3 ( 2 ); OMe ( 3 ); CF 3 ( 4 ); Cl ( 5 ); Br ( 6 )] were prepared according to the literature methods …”

Section: Methodsmentioning

confidence: 99%

Synthesis of a series of new ruthenium organometallic complexes derived from pyridine‐imine ligands and their catalytic activity in oxidation of secondary alcohols

Hao

et al. 2018

Applied Organom Chemis

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Reactions of pyridine imines [C5H4N‐2‐C(H) = N‐C6H4‐R] [R = H (1), CH3 (2), OMe (3), CF3 (4), Cl (5), Br (6)] with Ru3(CO)12 in refluxing toluene gave the corresponding dinuclear ruthenium carbonyl complexes of the type {μ‐η2‐CH[(2‐C5H4N)(N‐C6H4‐R)]}2Ru2(CO)4(μ‐CO) [R = H (7); CH3 (8); OMe (9); CF3 (10); Cl (11); Br (12)]. All six novel complexes were separated by chromatography, and fully characterized by elemental analysis, IR, NMR spectroscopy. Molecular structures of 7, 10, 11, and 12 were determined by X‐ray crystal diffraction. Further, the catalytic performance of these complexes was also tested. The combination of {μ‐η2‐CH[(2‐C5H4N)(N‐C6H4‐R)]}2Ru2(CO)4(μ‐CO) and NMO afforded an efficient catalytic system for the oxidation of a variety secondary alcohols.

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Studies of electronic effects of modified pyridine-imine ligands utilized in cobalt-catalyzed meta-selective Diels–Alder reactions

Cited by 14 publications

References 40 publications

1,4‐Cyclohexadienes—Easy Access to a Versatile Building Block via Transition‐Metal‐Catalysed Diels–Alder Reactions

1,4‐Cyclohexadienes—Easy Access to a Versatile Building Block via Transition‐Metal‐Catalysed Diels–Alder Reactions

Influences of Fluorine Substituents on Iminopyridine Fe(II)- and Co(II)-Catalyzed Isoprene Polymerization

Synthesis of a series of new ruthenium organometallic complexes derived from pyridine‐imine ligands and their catalytic activity in oxidation of secondary alcohols

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