The challenge of cyclic and acyclic schiff bases and related derivatives

International Tables for X-Ray Crystallography (Published for the International Union of Crystallography.) Vol. 1: Symmetry Groups. Edited by Norman F. M. Henry and Kathleen Lonsdale. Pp. xi + 558. (Birmingham: Kynoch Press, 1952.) 105s.

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International Tables for X-Ray Crystallography

This review is focused on the use of solid Lewis acids to promote catalytic oxidations. While the concept of using Lewis acids to promote the reaction of organic substrates with oxidizing reagents is widely accepted in homogeneous catalysis, this concept has not become evident and generally used in heterogeneous catalysis until recent days. Certainly the development of new Lewis acid solids active and selective for catalytic oxidations is an urgent need and a challenging scientific target for some substrates especially using environmentally friendly oxidants. Since the replacement of current stoichiometric oxidations for the production of fine chemicals by environmentally benign catalytic oxidations is one of the major tasks in green chemistry, solid Lewis acids are called to play a crucial role to accomplish this goal. In the review, we will see the still important role that stoichiometric oxidations play in our daily life, and how they are being substituted by catalytic oxidations. At this point, three general mechanisms in which Lewis acids are involved will be described, and the material has been organized starting from homogeneous and ending with solid catalysts for heterogeneous oxidations. A bridge between the two will be established by presenting catalytic systems that can fill the gap between the two systems helping to rationalize the nature of the catalytic active sites in solid systems. This review is obviously focused on solid oxidation catalysts, and the core of the review is organized to show the evolution from the simplest strategy for heterogeneizing homogeneous catalysts, i.e., supporting the active species on large surface area solids, to the more elaborate ones in which the active sites are part of the solid structure. Given the importance of metallosilicates, and more specifically titanosilicates, as catalysts in commercial processes, special attention has been paid to these types of materials. Although sufficient references are provided to early seminal work, special emphasis has been given to most recent contributions to this area, particularly of the last 10 years. Patent literature has also been extensively covered in this review. Examples to illustrate the concepts have been selected among recent publications, and an effort has been made to present a series of commercial and near commercial processes based on catalytic oxidations. Finally, two * E-mail: acorma@itq.upv.es. 3837 Chem. Rev. 2002, 102, 3837−3892

Lewis acids as catalysts in oxidation reactions: from homogeneous to heterogeneous systems.

N-silylated benzamidines: versatile building blocks in main group and coordination chemistry

https://escholarship.org/content/qt1kp1t47g/qt1kp1t47g.pdf?t=o0hb1w

Radical ligand-containing single-molecule magnets

The bulky amino-siloxide hybrid ligand −OSi(tBu)2((CH2)3NMe2) allows isolation of dinuclear, hydrocarbon-soluble barium complexes. The structures of two mono(ligand) complexes, {Ba[OSi(tBu)2((CH2)3...

Synthesis and structural characterization of barium complexes containing the bulky amino-siloxide hybrid ligand −OSi(tBu)2((CH2)3NMe2)

Trivalent lanthanide–alkene complexes: Crystallographic and NMR evidence for coordination of tethered alkenes in the solid state and solution

The synthesis of the protioligand 1,8-bis(2′-isopropyltetrazo-5′-yl)-3,6-di-tert-butylcarbazole, HCzTiPr2, is described. The acid–base reaction of 2 with various Ln[N(SiMe3)2]3 (Ln = Ce, Sm, Er, Yb, Y) precursors leads to products displaying a variety of different bonding modes for the CzTiPr− ligand as revealed by X-ray crystallographic studies. The smaller lanthanides form Ln(CzTiPr)[N(SiMe3)2]2 complexes (Ln = Er (3), Yb(4)) with a near planar, tridentate coordination mode for the CzTiPr− ligand. In contrast, the larger lanthanides form Ln(CzTiPr)2[N(SiMe3)2] complexes (Ln = Ce (5), Sm (6)) at room temperature that feature a sandwich structure with a highly distorted tridentate mode where tetrazole canting allows the metal to sit well out of the carbazole plane. Attempts to force additional CzTiPr− ligands onto Er or Yb at elevated temperature results in isolation of trace siloxide complexes Ln(CzTiPr)2(OSiMe3) (Ln = Er (3a), Yb (4a)) that adopt a flat tridentate ligand bonding mode similar to 3 and 4. Surprisingly, the high temperature reaction of 2 with Y[N(SiMe3)2]3 affords Y(CzTiPr)3, 7, featuring two tridentate and one bidentate CzTiPr ligands. Partial hydrolysis of 6 occurs over time to produce a hydroxo-bridged dimer that also features one bridging and one bidentate CzTiPr ligand, Sm(κ3-CzTiPr)(κ3-μ-CzTiPr)(μ-OH)2Sm(κ3-CzTiPr)(κ2-CzTiPr), 6a, further illustrating the remarkable coordinative flexibility of the CzTiPr ligand system.

Variable coordination of carbazolyl-bis(tetrazole) ligands in lanthanide chemistry

(.mu.-NO)2[Co(.eta.5-C5H5)]2 is not paramagnetic

The synthesis of tetrabenzo[a,c,g,i]fluorenyl (Tbf) yttrium dialkyl complexes, (Tbf)Y(CH2SiMe3)2(L) (L = tetrahydrofuran (THF), 1; L = bipy, 2), by direct protonolysis of the tris(alkyl) complex, Y(CH2SiMe3)3(THF)2, are reported. The X-ray crystal structures of 1 and 2 display the helical twisting typically observed for the Tbf ligand. Dynamic nuclear magnetic resonance (NMR) studies on 1 show a barrier to Tbf helical inversion (epimerization or “wagging”) of 38.1 ± 0.5 kJ mol−1. The reaction of 1 with acidic hydrocarbons such as 1,3-bis(trimethylsilyl)cyclopentadiene or trimethylsilylacetylene results in protonolysis to form the mixed Cp derivative [(Tbf){C5H3(SiMe3)2}Y(CH2SiMe3)(THF)] (3) or [(Tbf)Y(CCSiMe3)2(THF)]n (4), respectively. In the case of 4, a small amount of the trinuclear cluster (Tbf)Y3(μ3-CCSiMe3)2(μ2-CCSiMe3)3(CCSiMe3)3(THF)2 (5) was isolated and characterized by X-ray crystallography. Dialkyl 1 undergoes smooth insertion of trimethylsilyl isocyanate to afford [(Tbf)Y{κ2-(N,O)-Me3SiN(Me3...

https://tspace.library.utoronto.ca/bitstream/1807/75356/1/cjc-2016-0485.pdf

David J. Berg

Papers

Synthesis and structural characterization of barium complexes containing the bulky amino-siloxide hybrid ligand −OSi(tBu)2((CH2)3NMe2)

Trivalent lanthanide–alkene complexes: Crystallographic and NMR evidence for coordination of tethered alkenes in the solid state and solution

Variable coordination of carbazolyl-bis(tetrazole) ligands in lanthanide chemistry

(.mu.-NO)2[Co(.eta.5-C5H5)]2 is not paramagnetic

Supersize Cp! Tetrabenzo[a,c,g,i]fluorenyl complexes of yttrium