Catalytic Oxidations with Meta-Chloroperoxybenzoic Acid (m-CPBA) and Mono- and Polynuclear Complexes of Nickel: A Mechanistic Outlook

Selective catalytic functionalization of organic substrates using peroxides as terminal oxidants remains a challenge in modern chemistry. The high complexity of interactions between metal catalysts and organic peroxide compounds complicates the targeted construction of efficient catalytic systems. Among the members of the peroxide family, m-chloroperoxybenzoic acid (m-CPBA) exhibits quite complex behavior, where numerous reactive species could be formed upon reaction with a metal complex catalyst. Although m-CPBA finds plenty of applications in fine organic synthesis and catalysis, the factors that discriminate its decomposition routes under catalytic conditions are still poorly understood. The present review covers the advances in catalytic C–H oxidation and olefine epoxidation with m-CPBA catalyzed by mono- and polynuclear complexes of nickel, a cheap and abundant first-row transition metal. The reaction mechanisms are critically discussed, with special attention to the O–O bond splitting route. Selectivity parameters using recognized model hydrocarbon substrates are summarized and important factors that could improve further catalytic studies are outlined.

Composition and Corrosivity of Extracellular Polymeric Substances from The Hydrocarbon-Degrading Sulfate-Reducing Bacterium Desulfoglaeba alkanexedens ALDC

Sulfate-reducing bacteria (SRB) often exist as cell aggregates and in biofilms surrounded by a matrix of extracellular polymeric substances (EPSs). The chemical composition of EPSs may facilitate hydrophobic substrate biodegradation and promote microbial influenced corrosion (MIC). Although EPSs from non-hydrocarbon-degrading SRB have been studied; the chemical composition of EPSs from hydrocarbon-degrading SRBs has not been reported. The isolated EPSs from the sulfate-reducing alkane-degrading bacterium Desulfoglaeba alkanexedens ALDC was characterized with scanning and fluorescent microscopy, nuclear magnetic resonance spectroscopy (NMR), and by colorimetric chemical assays. Specific fluorescent staining and 1H NMR spectroscopy revealed that the fundamental chemical structure of the EPS produced by D. alkanexedens is composed of pyranose polysaccharide and cyclopentanone in a 2:1 ratio. NMR analyses indicated that the pyranose ring structure is bonded by 1,4 connections with the cyclopentanone directly bonded to one pyranose ring. The presence of cyclopentanone presumably increases the hydrophobicity of the EPS that may facilitate the accessibility of hydrocarbon substrates to aggregating cells or cells in a biofilm. Weight loss and iron dissolution experiments demonstrated that the EPS did not contribute to the corrosivity of D. alkanexedens cells.

A Photoredox-Catalyzed Approach for Formal Hydride Abstraction to Enable Csp3–H Functionalization with Nucleophilic Partners

While a great number of C–H functionalization methods have been developed in recent years, new mechanistic paradigms to deconstruct such bonds have been comparatively rare. Amongst possible strategies for breaking a C<i>_sp³</i>–H bond are deprotonation, oxidative addition with a metal catalyst, direct insertion via a nitrene intermediate, hydrogen atom transfer (HAT) with both organic and metal-based abstractors, and lastly, hydride abstraction. The latter is a relatively unexplored approach due to the unfavorable thermodynamics of such an event, and thus has not been developed as a general way to target both activated and unactivated C<i>_sp³</i>–H bonds on hydrocarbon substrates. Herein, we report our successful efforts in establishing a catalytic C–H functionalization manifold for accessing an intermediate carbocation by formally abstracting hydride from unactivated C<i>_sp³</i>–H bonds. The novel catalytic design relies on a stepwise strategy driven by visible light photoredox catalysis and is demonstrated in the context of a C–H fluorination employing nucleophilic fluorine sources. Difluorination of methylene groups is also demonstrated, and represents the first C–H difluorination with nucleophilic fluoride. Additionally, the formal hydride abstraction is shown to be amenable to several other classes of nucleophiles, allowing for the construction of C–C or C–heteroatom bonds.

A Photoredox-Catalyzed Approach for Formal Hydride Abstraction to Enable a General Csp3–H Fluorination with HF

While a great number of C–H functionalization methods have been developed in recent years, new mechanistic paradigms to deconstruct such bonds have been comparatively rare. Amongst possible strategies for breaking a C<i>_sp³</i>–H bond are deprotonation, oxidative addition with a metal catalyst, direct insertion via a nitrene intermediate, hydrogen atom transfer (HAT) with both organic and metal-based abstractors, and lastly, hydride abstraction. The latter is a relatively unexplored approach due to the unfavorable thermodynamics of such an event, and thus has not been developed as a general way to target both activated and unactivated C<i>_sp³</i>–H bonds on hydrocarbon substrates. Herein, we report our successful efforts in establishing a catalytic C–H functionalization manifold for accessing an intermediate carbocation by formally abstracting hydride from unactivated C<i>_sp³</i>–H bonds. The novel catalytic design relies on a stepwise strategy driven by visible light photoredox catalysis and is demonstrated in the context of a C–H fluorination employing nucleophilic fluorine sources. Difluorination of methylene groups is also demonstrated, and represents the first C–H difluorination with nucleophilic fluoride. Additionally, the formal hydride abstraction is shown to be amenable to several other classes of nucleophiles, allowing for the construction of C–C or C–heteroatom bonds.

A Photoredox-Catalyzed Approach for Formal Hydride Abstraction to Enable a General Csp3–H Fluorination with HF

While a great number of C–H functionalization methods have been developed in recent years, new mechanistic paradigms to deconstruct such bonds have been comparatively rare. Amongst possible strategies for breaking a C<i>_sp³</i>–H bond are deprotonation, oxidative addition with a metal catalyst, direct insertion via a nitrene intermediate, hydrogen atom transfer (HAT) with both organic and metal-based abstractors, and lastly, hydride abstraction. The latter is a relatively unexplored approach due to the unfavorable thermodynamics of such an event, and thus has not been developed as a general way to target both activated and unactivated C<i>_sp³</i>–H bonds on hydrocarbon substrates. Herein, we report our successful efforts in establishing a catalytic C–H functionalization manifold for accessing an intermediate carbocation by formally abstracting hydride from unactivated C<i>_sp³</i>–H bonds. The novel catalytic design relies on a stepwise strategy driven by visible light photoredox catalysis and is demonstrated in the context of a C–H fluorination employing nucleophilic fluorine sources. Difluorination of methylene groups is also demonstrated, and represents the first C–H difluorination with nucleophilic fluoride. Additionally, the formal hydride abstraction is shown to be amenable to several other classes of nucleophiles, allowing for the construction of C–C or C–heteroatom bonds.

Ligand-Driven Advances in Iridium Catalyzed sp3 C-H Borylation: 2,2’-Dipyridylarylmethane

The field of catalytic C-H borylation has grown considerably since its founding, providing a means for the preparation of synthetically versatile organoborane products. While sp2 C-H borylation methods have found widespread and practical use in organic synthesis, the analogous sp3 C-H borylation reaction remains challenging and has seen limited application. Existing catalysts are often hindered by incomplete consumption of the diboron reagent, poor functional group tolerance, harsh reaction conditions, and the need for excess or neat substrate. These challenges acutely affect C-H borylation chemistry of unactivated hydrocarbon substrates, which has lagged in comparison to methods for the C-H borylation of activated compounds. Herein we discuss recent advances in sp3 C-H borylation of undirected substrates in the context of two particular challenges: (1) utilization of the diboron reagent and (2) the need for excess or neat substrate. Our recent work on the application of dipyridylarylmethane ligands in sp3 C-H borylation has allowed us to make contributions in this space and has presented an additional ligand scaffold to supplement traditional phenanthroline ligands.

Moniliella spathulata, an oil-degrading yeast, which promotes growth of barley in oil-polluted soil

The yeast strain Moniliella spathulata SBUG-Y 2180 was isolated from oil-contaminated soil at the Tengiz oil field in the Atyrau region of Kazakhstan on the basis of its unique ability to use crude oil and its components as the sole carbon and energy source. This yeast used a large number of hydrocarbons as substrates (more than 150), including n-alkanes with chain lengths ranging from C10 to C32, monomethyl- and monoethyl-substituted alkanes (C9–C23), and n-alkylcyclo alkanes with alkyl chain lengths from 3 to 24 carbon atoms as well as substituted monoaromatic and diaromatic hydrocarbons. Metabolism of this huge range of hydrocarbon substrates produced a very large number of aliphatic, alicyclic, and aromatic acids. Fifty-one of these were identified by GC/MS analyses. This is the first report of the degradation and formation of such a large number of compounds by a yeast. Inoculation of barley seeds with M. spathulata SBUG-Y 2180 had a positive effect on shoot and root development of plants grown in oil-contaminated sand, pointing toward potential applications of the yeast in bioremediation of polluted soils. Key points • Moniliella spathulata an oil-degrading yeast • Increase of the growth of barley

Horizontal ‘gene drives’ harness indigenous bacteria for bioremediation

Engineering bacteria to clean-up oil spills is rapidly advancing but faces regulatory hurdles and environmental concerns. Here, we develop a new technology to harness indigenous soil microbial communities for bioremediation by flooding local populations with catabolic genes for petroleum hydrocarbon degradation. Overexpressing three enzymes (almA, xylE, p450cam) in Escherichia coli led to degradation of 60–99% of target hydrocarbon substrates. Mating experiments, fluorescence microscopy and TEM revealed indigenous bacteria could obtain these vectors from E. coli through several mechanisms of horizontal gene transfer (HGT), including conjugation and cytoplasmic exchange through nanotubes. Inoculating petroleum-polluted sediments with E. coli carrying the vector pSF-OXB15-p450camfusion showed that the E. coli cells died after five days but a variety of bacteria received and carried the vector for over 60 days after inoculation. Within 60 days, the total petroleum hydrocarbon content of the polluted soil was reduced by 46%. Pilot experiments show that vectors only persist in indigenous populations when under selection pressure, disappearing when this carbon source is removed. This approach to remediation could prime indigenous bacteria for degrading pollutants while providing minimal ecosystem disturbance.

Microbial Degradation of Different Hydrocarbon Fuels with Mycoremediation of Volatiles

Naturally occurring microorganisms in soil matrices play a significant role in overall hydrocarbon contaminant removal. Bacterial and fungal degradation processes are major contributors to aerobic remediation of surface contaminants. This study investigated degradation of conventional diesel, heating diesel fuel, synthetic diesel (Syntroleum), fish biodiesel and a 20% biodiesel/diesel blend by naturally present microbial communities in laboratory microcosms under favorable environmental conditions. Visible fungal remediation was observed with Syntroleum and fish biodiesel contaminated samples, which also showed the highest total hydrocarbon mineralization (>48%) during the first 28 days of the experiment. Heating diesel and conventional diesel fuels showed the lowest total hydrocarbon mineralization with 18–23% under favorable conditions. In concurrent experiments with growth of fungi suspended on a grid in the air space above a specific fuel with little or no soil, fungi were able to survive and grow solely on volatile hydrocarbon compounds as a carbon source. These setups involved negligible bacterial degradation for all five investigated fuel types. Fungal species able to grow on specific hydrocarbon substrates were identified as belonging to the genera of Giberella, Mortierella, Fusarium, Trichoderma, and Penicillium.