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

Platinum Complexes of Alkynyl-Substituted Dimethyldihydropyrenes

A series of lanthanide complexes, {[CpCo(P═O(OR)2)3]2Ln(H2O)x}+Cl– (Ln = Nd, 3; Eu, 4; Tb, 5; Yb, 6; R = Et, a; R = Ph, b) bearing two cobalt metalloligands were prepared. Electrospray mass spectrometry and thermogravimetric analysis suggest that the cations are either solvent-free or contain very weakly bound water molecules. The related complex {[CpCo(P═O(OPh)2)3]2Yb}+ [CoCl3(THF)]−, 7, was crystallographically characterized, and the cation in this case was confirmed to be 6-coordinate and solvent-free. Ligand exchange rates between the d0- and d60-isotopomers of 3a–6a and 5b were determined in acetonitrile by electrospray mass spectrometry. The ligand exchange rate was found to increase by almost 4 orders of magnitude from the smallest (Yb, 6a, k = 0.3 M–1 s–1) to largest ion (Nd, 3a, >2500 M–1 s–1) in acetonitrile. Additionally, the ligand exchange rate increased rapidly for 5a (Tb) with increasing water concentration from 30 M–1 s–1 in pure acetonitrile to 268 M–1 s–1 in 50:50 (v/v) acetonitrile/wate...

Lanthanide complexes of the Kläui metalloligand, CpCo(P═O(OR)2)3: an examination of ligand exchange kinetics between isotopomers by electrospray mass spectrometry.

A series of aminodiols RN(CH2CH2C(OH)Rprime2)2 (R, Rprime = Me, Me 4; Me, Ph 5; tert-butyl, Me 6; tert-Bu, Ph 7; (S)-PhCH(Me), Me 8) were prepared by the Michael addition of a primary amine to methyl acrylate followed by reaction of the resulting aminodiester with excess methyl or phenyl lithium. Reaction of two equivalents of the aminodiols 4-8 with tetrabenzylzirconium afforded the zirconium bis(aminodiolates) 10-14 in excellent yield. Complex 11 (R, Rprime = Me, Ph) adopts a cis, fac-octahedral geometry in solution and in the solid state. Complexes 10-14 are fluxional in solution by NMR spectroscopy: small substituents at nitrogen and large substituents at the alkoxide carbons slow the rate of exchange. The chiral complex 14 functions as a Lewis acid catalyst in the nitroaldol (Henry) reaction and the oxidation of geraniol by tert-butyl hydroperoxide with modest enantioselectivities (30 and 46% enantiomeric excess (ee), respectively).Key words: diol, Michael addition, zirconium, synthesis, structure, f...

Synthesis and structural characterization of zirconium complexes containing aminodiolate ligands and their use as Lewis acid catalysts

Novel, air-stable, yttrium and ytterbium complexes were found effective in the catalysis of the typical hetero Diels–Alder reaction of crotonaldehyde and ethylvinyl ether. They represent an attractive solution to the problem of ligand lability in the realm of lanthanide catalysts. Key words: lanthanide, catalyst, hetero Diels–Alder, yttrium, ytterbium.

Novel, air-stable, lanthanide catalysts for the hetero Diels–Alder reaction

Chelating triarylgermyl anions as ligands in lanthanide chemistry: synthesis of Ln[GeAr3]2 [Ar = C6H4(2-CH2NMe2); Ln = Sm, Yb] and the crystal structure of an unusual μ-(o-tolylene) digermane byproduct

David J. Berg

Papers

Platinum Complexes of Alkynyl-Substituted Dimethyldihydropyrenes

Lanthanide complexes of the Kläui metalloligand, CpCo(P═O(OR)2)3: an examination of ligand exchange kinetics between isotopomers by electrospray mass spectrometry.

Synthesis and structural characterization of zirconium complexes containing aminodiolate ligands and their use as Lewis acid catalysts

Novel, air-stable, lanthanide catalysts for the hetero Diels–Alder reaction

Chelating triarylgermyl anions as ligands in lanthanide chemistry: synthesis of Ln[GeAr3]2 [Ar = C6H4(2-CH2NMe2); Ln = Sm, Yb] and the crystal structure of an unusual μ-(o-tolylene) digermane byproduct