LongLarf

The scent of sustainability: White biotechnology has emerged in manufacturing processes to deliver perfumery ingredients satisfying novel interests of the society for natural, eco‐responsible, and sustainable materials. In this Minireview, we present a selection of novel biotechnological processes and ingredients encompassing combinations of state‐of‐the‐art approaches in biocatalysis, metabolic engineering, synthetic biology, biosynthesis elucidation, gene edition and cloning, and analytical chemistry.

Abstract

White biotechnology has emerged in biochemical manufacturing processes to deliver perfumery ingredients satisfying interests of the society for natural, eco‐responsible, and sustainable materials. As a result, an intense R&D activity has taken place on these subjects, resulting in both scientific publications and patent applications reporting combinations of state‐of‐the‐art approaches in biocatalysis, metabolic engineering, synthetic biology, biosynthesis elucidation, gene edition and cloning, and analytical chemistry. In this Minireview, a smelly selection of novel biotechnological processes and ingredients from a scientific articles and patents survey covering the last 6 years is presented and analysed in terms of chemistry, sustainability and naturality. Classification has been made between metabolic engineering on one side, allowing either biotechnological synthesis of essential oil surrogates or single molecule ingredients, and on the other side the optimisation of properties of natural complex substances by specific and selective enzymatic modifications of their chemical composition.

Si−Si bonds in polysilanes can be converted to Si−H bonds under mild conditions by using low‐valent anionic Ni⁰ hydride catalysts. The reaction is reversible and dehydrogenative coupling of hydrosilanes is also possible. Experiments and DFT calculations indicate that low‐coordinated 14‐ and 16‐electron d¹⁰‐Ni hydrides, silyl, and silane intermediates are involved in the catalytic cycle.

Abstract

The dehydrogenation of organosilanes (R _x SiH_4−x ) under the formation of Si−Si bonds is an intensively investigated process leading to oligo‐ or polysilanes. The reverse reaction is little studied. To date, the hydrogenolysis of Si−Si bonds requires very harsh conditions and is very unselective, leading to multiple side products. Herein, we describe a new catalytic hydrogenation of oligo‐ and polysilanes that is highly selective and proceeds under mild conditions. New low‐valent nickel hydride complexes are used as catalysts and secondary silanes, RR′SiH₂, are obtained as products in high purity.

Simple, illustrative words nicely explain the fundamental characteristics of organometallic compounds and their reactivity. For Group 4 metallocene complexes unusual descriptors like “tuck(ed)‐in”, “merry‐go‐round reaction”, and “sliding”, “migration”, or “tobogganing” have been used. These terms are explained and discussed in detail. Unusual wording is helpful for a better understanding of complex structures and reaction motifs.

Abstract

Three selected examples for the use of unusual wording to describe the organometallic chemistry of Group 4 metallocenes are explained and discussed. The term “tuck(ed)‐in” concerns the behavior of decamethyltitanocene [(C₅Me₅)₂Ti] and similar complexes in which one or two methyl groups form the titanium hydride complex [(C₅Me₅)(C₅Me₄CH₂)TiH] or other hydride complexes by C−H activation. In the so‐called “merry‐go‐round reaction” the rearrangement of C atoms bound to titanium in organometallic molecules is described which corresponds to the rotation of two C atoms along with a rotation of the six‐membered ring in a dihydroindenyl moiety at titanium. In the third example “migration” or “tobogganing” concerns the “sliding” of titanocene along the chain of a linear polyyne by coordination to one or more triple bonds. In all these reactions changes of the coordination mode of the metal at Cp or substrate ligands by intramolecular dynamics occur.

A highly active bifunctional organoboron catalyst with the advantages of scalable preparation, thermostability, and recyclability was reported for the cyclization of CO₂ and epoxides. An intramolecular cooperative mechanism was substantiated by investigations into the crystal structure of the catalysts, structure– performance relationships, kinetic studies, and the key reaction intermediates.

Abstract

A series of highly active organoboron catalysts for the coupling of CO₂ and epoxides with the advantages of scalable preparation, thermostability, and recyclability is reported. The metal‐free catalysts show high reactivity towards a wide scope of cyclic carbonates (14 examples) and can withstand a high temperature up to 150 °C. Compared with the current metal‐free catalytic systems that use mol % catalyst loading, the catalytic capacity of the catalyst described herein can be enhanced by three orders of magnitude (epoxide/cat.=200 000/1, mole ratio) in the presence of a cocatalyst. This feature greatly narrows the gap between metal‐free catalysts and state‐of‐the‐art metallic systems. An intramolecular cooperative mechanism is proposed and certified on the basis of investigations on crystal structures, structure–performance relationships, kinetic studies, and key reaction intermediates.

Sophisticated control: We demonstrate that secondary coordination sphere motifs can be applied to trigger a radical change in the electronic structure of copper complexes with a redox‐active guanidine ligand through ligand–metal intramolecular electron transfer (IET). Crown ether functions attached to the ligand allow manipulation of the degree of IET between the guanidine ligand and the copper atom through metal encapsulation.

Abstract

Intramolecular electron transfer (IET) between a redox‐active organic ligand and a metal in a complex is of fundamental interest and used in a variety of applications. In this work it is demonstrated that secondary coordination sphere motifs can be applied to trigger a radical change in the electronic structure of copper complexes with a redox‐active guanidine ligand through ligand–metal IET. Hence, crown ether functions attached to the ligand allow the manipulation of the degree of IET between the guanidine ligand and the copper atom through metal encapsulation.

Nature Catalysis, Published online: 24 August 2020; doi:10.1038/s41929-020-0495-0

Site selectivity and stereocontrol remain major challenges in C–H bond functionalization chemistry, especially in linear aliphatic saturated hydrocarbon scaffolds. We report the highly enantioselective and site-selective catalytic borylation of remote C(sp³)–H bonds to the carbonyl group in aliphatic secondary and tertiary amides and esters. A chiral C–H activation catalyst was modularly assembled from an iridium center, a chiral monophosphite ligand, an achiral urea-pyridine receptor ligand, and pinacolatoboryl groups. Quantum chemical calculations support an enzyme-like structural cavity formed by the catalyst components, which bind the substrate through multiple noncovalent interactions. Versatile synthetic utility of the enantioenriched -borylcarboxylic acid derivatives was demonstrated.

Fully electrified: For the first time, a electrochemical system for a one‐pot Wittig olefination reaction (WOR) is reported, which includes a very efficient recycling of triphenylphosphine from triphenylphosphine oxide waste and subsequent carbonyl olefinations through in situ base‐free Wittig ylide formation, avoiding chemical reductants or sacrificial electrodes.

Abstract

An unprecedented one‐pot fully electrochemically driven Wittig olefination reaction system without employing a chemical reductant or sacrificial electrode material to regenerate triphenylphosphine (TPP) from triphenylphosphine oxide (TPPO) and base‐free in situ formation of Wittig ylides, is reported. Starting from TPPO, the initial step of the phosphoryl P=O bond activation proceeds through alkylation with RX (R=Me, Et; X=OSO₂CF₃ (OTf)), affording the corresponding [Ph₃POR]⁺X⁻ salts which undergo efficient electroreduction to TPP in the presence of a substoichiometric amount of the Sc(OTf)₃ Lewis acid on a Ag‐electrode. Subsequent alkylation of TPP affords Ph₃PR⁺ which enables a facile and efficient electrochemical in situ formation of the corresponding Wittig ylide under base‐free condition and their direct use for the olefination of various carbonyl compounds. The mechanism and, in particular, the intriguing role of Sc³⁺ as mediator in the TPPO electroreduction been uncovered by density functional theory calculations.

What fluorine can do in CO₂ chemistry: Fluorinated materials in the form of homogeneous or heterogeneous states have demonstrated good performance in CO₂ chemistry in terms of capture and fixation. This Minireview focuses on the synthesis, characterization, performance, comparison, and interaction mechanism of the materials with CO₂ and other substrates, to shed light on the merits, outcomes, and potential progress in this field.

Abstract

CO₂ chemistry including capture and fixation has attracted great attention towards the aim of reducing the consumption of fossil fuels and CO₂ accumulation in the atmosphere. “CO₂‐philic” materials are required to achieve good performance owing to the intrinsic properties of the CO₂ molecule, that is, thermodynamic stability and kinetic inertness. In this respect, fluorinated materials have been deployed in CO₂ capture (physical and chemical pathway) or fixation (thermo‐ and electrocatalytic procedure) with good performances, including homogeneous (e. g., ionic liquids and small organic molecules) and heterogeneous counterparts (e. g., carbons, porous organic polymers, covalent triazine frameworks, metal–organic frameworks, and membranes). In this Minireview, these works are summarized and analyzed from the aspects of (1) the strategy used for fluorine introduction, (2) characterization of the targeted materials, (3) performance of the fluorinated systems in CO₂ chemistry, and comparison with the nonfluorinated counterparts, (4) the role of fluorinated functionalities in the working procedure, and (5) the relationship between performance and structural/electronic properties of the materials. The systematic summary in this Minireview will open new opportunities in guiding the design of “CO₂‐philic” materials and pave the way to stimulate further progress in this field.

As substitute for hazardous and gaseous phosgene, phenyl chloroformate enables the activation of alcohols to halo alkanes in the presence of an appropriate Lewis base catalyst. Indeed, 1‐formylpyrrolidine (FPyr) or diethylcyclopropenone (DEC) are crucial as catalytic species to drive the chemoselectivity from phenyl carbonate to the desired alkyl halide formation. The isolation of the by‐product phenol shows that conceptually a recycling by means of inexpensive phosgene is feasible.

Abstract

Nucleophilic substitutions (S _N ) are typically promoted by acid chlorides as sacrificial reagents to improve the thermodynamic driving force and lower kinetic barriers. However, the cheapest acid chloride phosgene (COCl₂) is a highly toxic gas. Against this background, phenyl chloroformate (PCF) was discovered as inherently safer phosgene substitute for the S _N ‐type formation of C−Cl and C−Br bonds using alcohols. Thereby, application of the Lewis bases 1‐formylpyrroldine (FPyr) and diethylcyclopropenone (DEC) as catalysts turned out to be pivotal to shift the chemoselectivity in favor of halo alkane generation. Primary, secondary and tertiary, benzylic, allylic and aliphatic alcohols are appropriate starting materials. A variety of functional groups are tolerated, which includes even acid labile moieties such as tert‐butyl esters and acetals. Since the by‐product phenol can be isolated, a recycling to PCF with inexpensive phosgene would be feasible on a technical scale. Eventually, a thorough competitive study demonstrated that PCF is indeed superior to phosgene and other substitutes.

Numerous redox transformations that are essential to life are catalyzed by metalloenzymes that feature Earth-abundant metals. In contrast, platinum-group metals have been the cornerstone of many industrial catalytic reactions for decades, providing high activity, thermal stability, and tolerance to chemical poisons. We assert that nature’s blueprint provides the fundamental principles for vastly expanding the use of abundant metals in catalysis. We highlight the key physical properties of abundant metals that distinguish them from precious metals, and we look to nature to understand how the inherent attributes of abundant metals can be embraced to produce highly efficient catalysts for reactions crucial to the sustainable production and transformation of fuels and chemicals.

As substitute for hazardous and gaseous phosgene, phenyl chloroformate enables the activation of alcohols to halo alkanes in the presence of an appropriate Lewis base catalyst. Indeed, 1‐formylpyrrolidine (FPyr) or diethylcyclopropenone (DEC) are crucial as catalytic species to drive the chemoselectivity from phenyl carbonate to the desired alkyl halide formation. The isolation of the by‐product phenol shows that conceptually a recycling by means of inexpensive phosgene is feasible.

Abstract

Nucleophilic substitutions (S _N ) are typically promoted by acid chlorides as sacrificial reagents to improve the thermodynamic driving force and lower kinetic barriers. However, the cheapest acid chloride phosgene (COCl₂) is a highly toxic gas. Against this background, phenyl chloroformate (PCF) was discovered as inherently safer phosgene substitute for the S _N ‐type formation of C−Cl and C−Br bonds using alcohols. Thereby, application of the Lewis bases 1‐formylpyrroldine (FPyr) and diethylcyclopropenone (DEC) as catalysts turned out to be pivotal to shift the chemoselectivity in favor of halo alkane generation. Primary, secondary and tertiary, benzylic, allylic and aliphatic alcohols are appropriate starting materials. A variety of functional groups are tolerated, which includes even acid labile moieties such as tert‐butyl esters and acetals. Since the by‐product phenol can be isolated, a recycling to PCF with inexpensive phosgene would be feasible on a technical scale. Eventually, a thorough competitive study demonstrated that PCF is indeed superior to phosgene and other substitutes.

The repository Chemotion provides solutions for current challenges to store research data in a feasible manner. A main advantage of Chemotion is the comprehensive functionality, offering options to collect, prepare, and reuse data with discipline‐specific methods and data‐processing tools.