Robby Vroemans

Publication date: 15 November 2022

Source: Coordination Chemistry Reviews, Volume 471

Author(s): Xinlong Lin, Sue-Faye Ng, Wee-Jun Ong

Nature Synthesis, Published online: 04 August 2022; doi:10.1038/s44160-022-00129-x

The 20π porphyrinoids are immediate higher homologues of 18π porphyrins which shows intriguing structural and spectral properties depending on their aromaticity. The review summarises the synthetic strategies and properties of this unique class of porphyrinoids.

Abstract

The 20π porphyrinoids are immediate higher homologues of 18π porphyrins and differ from porphyrins in aromaticity which in turn affects the structure, properties and chemical reactivities. Research over the years indicated that the 20π porphyrinoids can be stabilized as non-aromatic/anti-aromatic or Mobius aromatic macrocycles using different strategies such as core-modification of porphyrins, non-metal/metal complexation of porphyrins, peripheral modification of porphyrins and expanded porphyrinoids. The structural properties such as aromaticity of the macrocycle can be controlled by choosing the right synthetic strategy. This review will provide an overview of the development in the chemistry of 20π porphyrinoids giving emphasize on the synthesis, structure and electronic properties of these macrocycles which have huge potential for various applications.

Tertiary amines from lignin model monomers: A heterogeneous Cu-ZrO₂ catalyzed hydrogen borrowing strategy was developed to synthesize tertiary amines from lignin (model) monomers. Reusability of the easily recoverable catalyst was investigated by recycle experiments and in depth analysis of the spent catalyst (ToF-SIMS, N₂O chemisorption, XPS and TGA). Thermal reduction proved to be an efficient catalyst regeneration strategy.

Abstract

Upcoming biorefineries, such as lignin-first provide renewable aromatics containing unique aliphatic alcohols. In this context, a Cu-ZrO₂ catalyzed hydrogen borrowing approach was established to yield tertiary amine from the lignin model monomer 3-(3,4-dimethoxyphenyl)-1-propanol and the actual lignin-derived monomers, (3-(4-hydroxyphenyl)-1-propanol and dihydroconiferyl alcohol), with dimethylamine. Various industrial metal catalysts were evaluated, resulting in nearly quantitative mass balances for most catalysts. Identified intermediates, side and reaction products were placed into a corresponding reaction network, supported by kinetic evolution experiments. Cu-ZrO₂ was selected as most suitable catalyst combining high alcohol conversion with respectable aliphatic tertiary amine selectivity. Low pressure H₂ was key for high catalyst activity and tertiary amine selectivity, mainly by hindering undesired reactant dimethylamine disproportionation and alcohol amidation. Besides dimethylamine model, diverse secondary amine reactants were tested with moderate to high tertiary amine yields. As most active catalytic site, highly dispersed Cu species in strong contact with ZrO₂ is suggested. ToF-SIMS, N₂O chemisorption, TGA and XPS of spent Cu-ZrO₂ revealed that imperfect amine product desorption and declining surface Cu lowered the catalytic activity upon catalyst reuse, while thermal reduction readily restored the initial activity and selectivity demonstrating catalyst reuse.

A single-step construction of atropisomers with vicinal C−C and C−N chiral diaxes by cyclopentadiene (Cp)-free cobalt-catalyzed intramolecular atroposelective C−H annulation with decent stereocontrols (up to >99 % ee and 70/1 dr) was reported. Atropisomerization experiments and DFT calculations are done to study the rotational barriers and pathways of the diaxes.

Abstract

The atroposelective synthesis of atropisomers with vicinal diaxes remains rare and challenging, due to the steric influence between the two axes and their unique topology. Herein, we disclose a single-step construction of atropisomers with vicinal C−C and C−N chiral diaxes by cyclopentadiene (Cp)-free cobalt-catalyzed intramolecular atroposelective C−H annulation, providing the desired diaxial atropisomers of unique structures with decent stereocontrols of both axes (up to >99 % ee and 70 : 1 dr). The optically pure products bearing fluorophores show circular polarized luminescence (CPL) properties, being candidate materials for potential CPL applications. Atropisomerization experiments and density function theory (DFT) calculations are conducted to study the rotational barriers and rotation pathways of the diaxes.

The transformation of olefins to branched amines is presented by combining a hydroformylation/aldol condensation tandem reaction with the reductive amination in a combined multiphase system that each can be recycled 9 times. The product phase of the first system is the substrate phase for the second recycling. The yields are stable during those recycling runs and the leaching is low with 0.09 % over the two recycling stages.

Abstract

This study presents the transformation of olefins to branched amines by combining a hydroformylation/aldol condensation tandem reaction with the reductive amination in a combined multiphase system that can be recycled 9 times. The products are branched amines that are precursors for surfactants. Since the multiphase hydrofomylation/aldol condensation system has already been studied, the first step was to develop the partial hydrogenation of unsaturated aldehydes together with a subsequent reductive amination. The rhodium/phosphine catalyst is immobilized in a polar polyethylene phase which separates from the product phase after the reaction. Reaction and catalyst recycling are demonstrated by the conversion of the C₁₄-aldehyde 2-pentylnonenal with the dimethylamine surrogate dimethylammonium dimethylcarbamate to the corresponding tertiary amine with yields up to 88 % and an average rhodium leaching of less than 0.1 % per recycling run. Furthermore, the positive influence of a Bronsted acid and carbon monoxide on the selectivity are discussed. Finally, the two PEG based systems have been merged in one recycling approach, by using the product phase of the hydroformylation aldol condensation reaction for the reductive amination reaction. The yields are stable during a nine recycling runs and the leaching low with 0.09 % over the two recycling stages.

Synlett
DOI: 10.1055/a-1890-9162

Electrosynthesis is undergoing a renaissance, but it is still far from being considered a standard method within the chemists’ synthetic toolbox. In this article, we will demystify organic electrochemistry by reviewing some practical methodologies developed in our laboratory to prepare highly reactive synthetic intermediates.1 Introduction2 Acyloxy Radicals3 Orthoesters4 Isocyanates5 Isocyanides6 Diazo Compounds7 Conclusion
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

Article in Thieme eJournals:
Table of contents  |  Abstract  |  Full text

The direct chemoselective carbonylative cross-coupling reaction of allylic alcohols and organoalanes with 1 atm CO via nickel catalysis has been developed to access the β,γ-unsaturated ketones with broad scope. The use of organoalanes as both the coupling components and the activators for the alcohol functionalization was found to be both crucial and advantageous as the method does not require any external activators.

Abstract

A nickel-catalyzed three-component carbonylative cross-coupling reaction of allylic alcohols and organoalanes with CO at atmospheric pressure is reported, enabling the expedient formation of β,γ-unsaturated ketones with broad scope. Particularly, the chemoselective allylic carbonylation of diols further highlights the practicability of this protocol. The leverage of organoalanes as both the coupling components and the activators for the alcohol functionalization is crucial for this method, thus no extraneous activators are required.