New Nickel(II) Complexes with N-donor Ligands and Anions as Coligands PDF Download
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Author: Vladislav Abramov
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Author: Vladislav Abramov
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 494
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Author: Abhijit Pramanik
Publisher:
ISBN:
Category :
Languages : en
Pages : 95
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Ni(II) pincer complexes are among the most important and useful compounds in homogeneous catalysis. Significant advancement has been made in this field in recent years. Many Ni(II) pincer complexes have been prepared and utilized in various catalytic reactions e.g. cross coupling reactions, C-H activation, carbon dioxide activation etc. Still, nickel(II) complexes supported by the pincer ligand with three nitrogen donors are relatively less explored and catalytic applications with those complexes are scarce in literature. This thesis describes the synthesis of a new pyrrolyl pyridine based pincer ligand and its Ni(II) complexes. The pyrrolyl pyridine pincer ligand, a relatively new class of dianionic, tridentate, nitrogen-based ligands in coordination chemistry, was prepared starting with a modified method for the synthesis of pyrrolyl pyridine. This modified procedure is simpler, less time consuming making it cheaper than the classical method and provides 2,6-bis(3,5-ditolyl-2-pyrrolyl)pyridine in good yields. Reaction of its potassium salt with Ni(OTf)2 resulted in three different stable nickel(II) pincer complexes. The novel nickel(II) pincer complexes were fully characterized by 1H NMR spectroscopy, 13C NMR spectroscopy, infrared spectroscopy and high resolution mass spectrometry. The X-ray crystal structures of the new ligand and metal complexes have been described.
Author: Jelena Jenter
Publisher: Cuvillier Verlag
ISBN: 3736933428
Category : Science
Languages : en
Pages : 134
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Bis(phosphinimino)methanide rare earth metal bisborohydrides, as illustrated in Scheme I, were successfully synthesized by salt metathesis reactions of [K{CH(PPh2NSiMe3)2}] with [Ln(BH4)3(THF)n] (Ln = Sc (n = 2); Ln = La, Nd, Lu (n = 3)) or in the case of yttrium by the reaction of [{(Me3SiNPPh2)2CH}YCl2]2 with NaBH4. Interestingly, the BH4- anions are ?3-coordinated in the solid state structures of 3, 4, 6 and 7, while for the scandium complex 5 two different conformational polymorphs were identified, in which either both BH4- groups are ?3-coordinated or one BH4- anion shows an ?2-coordination mode. Furthermore, complexes 3, 6 and 7 showed high activities in the ring-opening polymerization (ROP) of e-caprolactone (CL). At 0 °C, the molar mass distribution reached the narrowest values ever obtained for the ROP of CL initiated by a rare earth metal borohydride species. In collaboration with N. Meyer, rare earth metal chlorides and borohydrides of the 2,5-bis{N-(2,6-diisopropylphenyl)iminomethyl}pyrrolyl ligand were synthesized, as shown in Scheme II. The reaction of [(DIP2pyr)K] (10) with anhydrous neodymium trichloride afforded [(DIP2pyr)NdCl2(THF)]2 (12) which is dimeric in the solid state. Excitingly, the reaction of [(DIP2pyr)K] (10) with [Ln(BH4)3(THF)n] (Ln = Sc (n = 2); Ln = La, Nd, Lu (n = 3)) depends on the ionic radii of the center metals. For the larger rare earth metals lanthanum and neodymium, the expected products [(DIP2pyr)Ln(BH4)2(THF)2] (Ln = La (13), Nd (14)) were obtained; while for the smaller rare earth metals scandium and lutetium, an unusual redox reaction of a BH4- anion with one of the Schiff-base functions of the ligand was observed and the products [{DIP2pyr*-BH3}Ln(BH4)(THF)2] (Ln = Sc (15), Lu (16)) were formed (Scheme II). Moreover, the two neodymium containing complexes 12 and 14 were investigated as Ziegler-Natta catalysts for the polymerization of 1,3-butadiene to form poly-cis-1,4-butadiene, by using various cocatalyst mixtures. Very high activities and good selectivities were observed for 12. The 2,5-bis{N-(2,6-diisopropylphenyl)iminomethyl}pyrrolyl ligand was successfully introduced into the coordination chemistry of the divalent lanthanides and the alkaline earth metals. As shown in Scheme III, salt metathesis reactions of [(DIP2pyr)K] (10) with either anhydrous lanthanide diiodides or alkaline earth metal diiodides afforded the corresponding heteroleptic iodo complexes [(DIP2pyr)LnI(THF)3] (Ln = Sm (19), Eu (20), Yb (21)) or [(DIP2pyr)MI(THF)n] (M = Ca (24), Sr (22) (n = 3); Ba (23) (n = 4)). Surprisingly, all complexes 19-24 are monomeric in the solid state, independently from the ionic radii of their center metals. Instead of forming dimers, the coordination sphere of each metal center is satisfied by additionally coordinated THF molecules, which is a very rare structural motif in the chemistry of the larger divalent lanthanides and alkaline earth metals. While the (DIP2pyr)- ligands in 19-23 are ?3-coordinated in the solid state, for the calcium complex 24 an ?2-coordination mode was observed (Scheme III). Interestingly, the calcium complex 24 and the analogous ytterbium compound 21 show different structures in the solid state. In order to obtain catalytically active species, [(DIP2pyr)M{N(SiMe3)2}(THF)2] (M = Ca (25), Sr (26)) were prepared by the reaction of [(DIP2pyr)MI(THF)3] (M = Ca (24), Sr (22)) with [K{N(SiMe3)2}] (Scheme IV). Compounds 25 and 26 were investigated for the intramolecular hydroamination of aminoalkenes and one aminoalkyne. Unfortunately, both catalysts exhibit a limited reaction scope, caused by the formation of undesired side products by alkene isomerization and imine-enamine tautomerism. However, both compounds are active catalysts and show high yields and short reaction times. The highest activities were observed for the calcium complex 25 and can be compared to the results obtained with the ß-diketiminato calcium amide [{(DIPNC(Me))2CH}Ca{N(SiMe3)2}(THF)] as a catalyst. Finally, imidazolin-2-imide and cyclopentadienyl-imidazolin-2-imine rare earth metal alkyl complexes, synthesized by M. Tamm et al., were investigated for the intramolecular hydroamination of non-activated aminoalkenes and one aminoalkyne. Both compounds showed high selectivities and activities, and although they cannot compete with the metallocene analogues, the imidazolin-2-imide complexes are new and interesting examples for catalytically active post-metallocenes.
Author: Major Curt Thompson
Publisher:
ISBN:
Category : Nickel
Languages : en
Pages : 82
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Author: Michael Joseph Goldcamp
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Ligands containing two oxime donor groups with a variable third group in a tripodal amine motif have been designed and synthesized. Their Ni(II) complexes, and some Zn(II), Cu(II), and Fe(III) complexes, have been structurally and spectroscopically characterized. Deprotonation of the oxime groups gives Ni(II)--Polyoximate complexes that form bis(N-O) oximate bridged dimers with significantly low oxidation potentials for Ni(II). These Ni(II)-polyoximate complexes react with dioxygen, consuming multiple equivalents. This is unusual chemistry for Ni(II), especially in the absence of ligand oxidation. The Ni(II) / O 2 reaction system promotes oxidation of triphenyl phosphine, with oxygen atom transfer, benzyl alcohol, and 3,5-di-tert-butylcatechol. Reaction of the Ni(II)-polyoximate complexes with o-quinones causes the formation of high-valent nickel complexes of the reduced dioxolenes, semiquinones and catecholates.
Author: Julie Victoria Gilligan
Publisher:
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Category :
Languages : en
Pages : 0
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Author: Lou Anne Kayser
Publisher:
ISBN:
Category : DNA-ligand interactions
Languages : en
Pages : 270
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Author: Lars Valentin
Publisher:
ISBN:
Category :
Languages : en
Pages : 189
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Author: James Randolph Preer
Publisher:
ISBN:
Category :
Languages : en
Pages : 408
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