Search

The reaction chemistry of the bis-tetrazinyl pyridine ligand (btzp) towards nitrogen oxyanions coordinated to zinc is studied in order to explore the reduction of the NOx- substrates with a redox-active ligand in the absence of redox activity at the metal. Following syntheses and characterization of (btzp)ZnX2 for X=Cl, NO3 and NO2 , featuring O-Zn linkage of both nitrogen oxyanions, it is shown that a silylating agent selectively delivers silyl substituents to tetrazine nitrogens, without reductive deoxygenation of NOx-1 . A new synthesis of the highly hydrogenated H4 btzp, containing two dihydrotetrazine reductants is described as is the synthesis and characterization of (H4 btzp)ZnX2 for X=Cl and NO3 , both of which show considerable hydrogen bonding potential of the dihydrotetrazine ring NH groups. The (H4 btzp)ZnCl2 complex does not bind zinc in the pincer pocket, but instead H4 btzp becomes a bridge between neighboring atoms through tetrazine nitrogen atoms, forming a polymeric chain. The reaction of AgNO2 with (H4 btzp)ZnCl2 is shown to proceed with fast nitrite deoxygenation, yielding water and free NO. Half of the H4 btzp reducing equivalents form Ag0 and thus the chloride ligand remains coordinated to the zinc metal center to yield (btzp)ZnCl2 . To compare with AgNO2 , experiments of (H4 btzp)ZnCl2 with NaNO2 result in salt metathesis between chloride and nitrite, highlighting the importance of a redox-active cation in the reduction of nitrite to NO.

The transition-metal-catalyzed cyclopropanation of alkenes by the decomposition of diazo compounds is a powerful and straightforward strategy to produce cyclopropanes, but is tempered by the potentially explosive nature of diazo substrates. Herein we report the Mo-catalyzed regiospecific deoxygenative cyclopropanation of readily available and bench-stable 1,2-dicarbonyl compounds, in which one of the two carbonyl groups acts as a carbene equivalent upon deoxygenation and engages in the subsequent cyclopropanation process. The use of a commercially available Mo catalyst afforded an array of valuable cyclopropanes with exclusive regioselectivity in up to 90 % yield. The synthetic utility of this method was further demonstrated by gram-scale syntheses, late-stage functionalization, and the cyclopropanation of a simple monocarbonyl compound. Preliminary mechanistic studies suggest that phosphine (or silane) acts as both a mild reductant and a good oxygen acceptor that efficiently regenerates the catalytically active Mo catalyst through reduction of the Mo-oxo complexes.

Bis(silylethynylated) 5,7‐ and 5,12‐diazapentacenes were synthesized from cis‐ and trans‐quinacridone using protection, alkynylation and deoxygenation. The solid‐state packing of the targets is determined by choice and position of the silylethynyl substituents. The position of the substituents and nitrogen atoms influence the optical properties of the targets., Piecing together a diazaacene: Starting from linear cis‐ and trans‐quinacridones, the synthesis, characteristics and stability of four diazapentacenes are reported leading to a design rule for 12,14‐alkynylated heteroacenes for organic electronics (see figure).

Xylitol is commonly known as one of the top platform intermediates for biomass conversion. Catalytic deoxygenation of xylitol provides an atomic and energetic efficient way to produce a variety of renewable chemicals including ethylene glycol, 1,2-propanediol, lactic acid and 1,4-anhydroxylitol. Despite a few initial attempts in converting xylitol into those products, improving catalyst selectivity towards C-O and C-C cleavage reactions remains a grand challenge in this area. To our best knowledge, there is lack of comprehensive review to summarize the most recent advances on catalyst design and mechanisms in deoxygenation of xylitol, offering important perspective into future development of xylitol transformation technologies. Therefore, in this mini-review, we have critically discussed the conversion routes involved in xylitol deoxygenation over solid catalyst materials, the nanostructures of supported metal catalysts for C-H, C-C and C-O bond cleavage reactions, and mechanistic investigation for xylitol conversion. The outcome of this work provides new insights into rational design of effective deoxygenation catalyst materials for upgrading of xylitol and future process development in converting hemicellulosic biomass.

Using fatty acids as renewable sources of biofuels requires deoxygenation. While a number of promising catalysts have been developed to achieve this, their operating mechanisms are poorly understood. Here, model molecular systems are studied in the gas phase using mass spectrometry experiments and DFT calculations. The coordinated metal complexes [(phen)M(O2CR)]+ (where phen=1,10‐phenanthroline; M=Ni or Pd; R=CnH2n+1, n≥2) are formed via electrospray ionization. Their collision‐induced dissociation (CID) initiates deoxygenation via loss of CO2 and [C,H2,O2]. The CID spectrum of the stearate complexes (R=C17H35) also shows a series of cations [(phen)M(R’)]+ (where R’ 17) separated by 14 Da (CH2) corresponding to losses of C2H4‐C16H32 (cracking products). Sequential CID of [(phen)M(R’)]+ ultimately leads to [(phen)M(H)]+ and [(phen)M(CH3)]+, both of which react with volatile carboxylic acids, RCO2H, (acetic, propionic, and butyric) to reform the coordinated carboxylate complexes [(phen)M(O2CR)]+. In contrast, cracking products with longer carbon chains, [(phen)M(R)]+ (R>C2), were unreactive towards these carboxylic acids. DFT calculations are consistent with these results and reveal that the approach of the carboxylic acid to the “free” coordination site is blocked by agostic interactions for R > CH3.

Catalytic deoxygenation of even-numbered fatty acids into odd-chain linear α-olefins (LAOs) has emerged as a complementary strategy to oligomerization of ethylene, which only affords even-chain LAOs. Although enzymes and homogeneous catalysts have shown promising potential for this application, industrial production of LAOs through these catalytic systems is still very difficult to accomplish to date. A recent breakthrough involves the use of an expensive noble-metal catalyst, Pd/C, through a phosphine ligands-assisted method for LAOs production from fatty acid conversion. This study presents a unique, cost-friendly, non-noble bimetallic NiFe/C catalyst for highly selective LAOs production from fatty acids through decarbonylative dehydration. In the presence of acetic anhydride and phosphine ligand, a remarkable improvement in the yield of 1-heptadecene from the conversion of stearic acid was found over the supported bimetallic catalyst (NiFe/C) as compared to corresponding monometallic counterparts (Ni/C and Fe/C). Through optimization of the reaction conditions, a 70.1 % heptadecene yield with selectivity to 1-heptadecene as high as 92.8 % could be achieved over the bimetallic catalyst at just 190 °C. This unique bimetallic NiFe/C catalyst is composed of NiFe alloy in the material bulk phase and a surface mixture of NiFe alloy and oxidized NiFeδ+ species, which offer a synergized contribution towards decarbonylative dehydration of stearic acid for 1-heptadecene production.

The use of carbon monoxide as a direct reducing agent for the deoxygenation of terminal and internal epoxides to the respective olefins is presented. This reaction is homogeneously catalyzed by a carbonyl pincer‐iridium(I) complex in combination with a Lewis acid co‐catalyst to achieve a pre‐activation of the epoxide substrate, as well as the elimination of CO2 from a γ‐2‐iridabutyrolactone intermediate. Especially terminal alkyl epoxides react smoothly and without significant isomerization to the internal olefins under CO atmosphere in benzene or toluene at 80–120 °C. Detailed investigations reveal a substrate‐dependent change in the mechanism for the epoxide C−O bond activation between an oxidative addition under retention of the configuration and an SN2 reaction that leads to an inversion of the configuration., Deoxygenate it! Carbon monoxide is the direct and environmentally benign deoxygenation agent for epoxides. This reaction is catalyzed by an iridium pincer complex and co‐catalyst LiNTf2 via an unprecedented γ‐2‐iridabutyrolactone intermediate. LiNTf2 is not only necessary for the epoxide activation, but also for the decarboxylation of the iridalactone (see scheme).

Deoxygenation in coastal and open-ocean ecosystems rarely exists in isolation but occurs concomitantly with acidification. Here, we first combine meta-data of experimental assessments from across the globe to investigate the potential interactive impacts of deoxygenation and acidification on a broad range of marine taxa. We then characterize the differing degrees of deoxygenation and acidification tested in our dataset using a ratio between the partial pressure of oxygen and carbon dioxide (pO2 /pCO2 ) to assess how biological processes change under an extensive, yet diverse range of pO2 and pCO2 conditions. The dataset comprised 375 experimental comparisons and revealed predominantly additive but variable effects (91.7%, additive; 6.0%, synergistic; and 2.3%, antagonistic) of the dual stressors, yielding negative impacts across almost all responses examined. Our data indicate that the pO2 /pCO2 -ratio offers a simplified metric to characterize the extremity of the concurrent stressors and shows that more severe impacts occurred when ratios represented more extreme deoxygenation and acidification conditions. Importantly, our analysis highlights the need to assess the concurrent impacts of deoxygenation and acidification on marine taxa and that assessments considering the impact of O2 depletion alone will likely underestimate the impacts of deoxygenation events and their ecosystem-wide consequences.

European rivers experience increased loading of total organic carbon (TOC) from terrestrial sources due to factors involving changes in land use, climate and soil acidity. However, little is known about how increased TOC is linked to changes in the bioreactivity of organic matter in these rivers on a continental scale. We compiled paired measurements of TOC and biological oxygen demand in 5‐day 20°C dark incubations from 3,486 EU monitoring rivers. Assuming first‐order decay and a fixed respiratory quotient, annual average TOC and biological oxygen demand values were used to calculate 11,060 values of the decay coefficient k . The k decreased by two orders of magnitude as a power function of increasing TOC. This relationship could partly be explained by carbon quality, as the C:N ratio of the organic matter was the lowest in high‐reactivity low‐TOC rivers, and vice versa. A trend analysis showed that TOC increased by 18% from 1996 to 2012, while k decreased by as much as 50%. As a consequence, the biological oxygen demand in the water decreased over time in spite of the water browning trend (increased TOC). Together, these results suggest that reactivity is low near terrestrial hot spots for TOC export, and low during years with high terrestrial TOC loading, but increases in rivers with low TOC concentrations where internal processes in the water have high relative influence on bulk TOC quality. Thus, browning of European freshwaters is linked to strong decreases in TOC reactivity on a continental scale, suggesting that the impacts of browning on microbial water deoxygenation and greenhouse gas production are less severe than previously thought. (Less)

In this study, we report catalytic fast pyrolysis of biomass using multifunctional hybrid spinel-oxide@zeolite catalysts prepared by using the steam-assisted crystallization (SAC) method to create the mesoporous zeolite followed by urea hydrolysis of metal nitrates to deposit spinel-oxides. This hybrid catalyst was quite effective in the deoxygenation of pinewood sawdust pyrolysis vapours, while avoiding over cracking of the lignin precursors, which are already ideal as chemical and fuel precursors. In the first step, multiple spinel oxides MgB2O4 (where B=Fe, Al, Ce, Ga, Cr) were screened as catalysts for the pyrolysis of pinewood sawdust and the resultant bio-oil (bio-oil on the water-free basis) was assessed in terms of carbon efficiency, oxygen content and chemical composition. While all the tested spinel oxides deoxygenated the pyrolysis vapour, MgAl2O4 and MgFe2O4 were found to provide a well-balanced deoxygenation degree and producing bio-oil with acceptable carbon efficiency. Catalytic activity and product distribution were affected by the density and strength of the acid sites of the spinel oxides. Subsequently, CFP over MgFe2O4@ZSM5 and MgAl2O4@ZSM5 was investigated under similar condition. The better performance of the hybrid catalyst was attributed to the deposition of small particles of MgFe2O4 in the external surface of the zeolite. The presence of this spinel oxide on the external surface depolymerized bulky oxygenates to lighter fractions that could easily access the active sites within the mesoporous structure of the zeolite, thus providing the catalytic function needed for the oxygen removal after aromatic ring saturation.

The simple and efficient conversion of carbonyl compounds into functionalized alkanes via deoxygenation is highly enabling in chemical synthesis. This Review covers the recent methodology development in carbonyl and carboxyl deoxygenative functionalizations, highlighting some representative and significant contributions in this field. These advances are categorized based on the reactivity patterns of some oxygenated feedstock compounds, including aldehydes, ketones and carboxylic acids. Four types of reactive intermediates arising from aldehydes and ketones during the deoxygenation, namely, bis-electrophiles, carbenoids, bis-nucleophiles and alkyl radical equivalents, are presented, while the carboxylic acids mainly behave as tris-electrophiles when deoxygenated. In each subcategory, selected examples are organized according to the type of bond formation and discussed from a generalized mechanistic perspective.

We report a novel example of electro-mediated photoredox catalysis (e-PRC) in the reductive cleavage of C(sp 3 )-O bonds of phosphinated alcohols to alkyl carbanions. As well as deoxygenations, olefinations are reported which are E -selective and can be made Z -selective in a tandem reduction/photosensitization process where both steps are photoelectrochemically promoted. Spectroscopy, computation and catalyst structural variations reveal that our new naphthalene monoimide-type catalyst allows for a more intimate dispersive precomplexation of its radical anion form with the phosphinate substrate, facilitating a reactivity-determining C(sp 3 )-O cleavage. Surprisingly and in contrast to previously reported photoexcited radical anion chemistries, our conditions i) tolerate aryl chlorides/bromides and ii) do not give rise to Birch-type reductions., Accepted Article

Deoxygenation of heteroaromatic N-oxides is commonly accomplished using chemical or enzymatic methods. In this work, we report on an expedient protocol for electrochemical reduction of pyridine N-oxide derivatives under mild conditions. A diverse range of mono- and bis-N-oxides were converted into the corresponding nitrogen bases in good yields. Importantly, the method is highly selective towards N-oxides and tolerates challenging halo and nitro substituents in the heteroaromatic ring.

We have demonstrated B2 pin2 as superior deoxidizing agent for the reductive deoxygenation of quinol derivatives under basic conditions. A wide range of highly functionalized phenols were obtained in good yields including a complex drug molecule, which revealed the high functional group tolerance of this protocol.

The Ψ[CH2 NH] reduced amide bond is a peptide isostere widely used in the development of bioactive pseudopeptides. Reported here is a method of chemoenzymatic posttranslational modification for the synthesis of Ψ[CH2 NH]-containing peptides converted from ribosomally expressed peptides. The posttranslational conversion composed of an enzymatic cyclodehydration and facile two-step chemical reduction achieves deoxygenation of a specific amide bond present in a nonprotected peptide in water. This method generates the Ψ[CH2 NH] bond in peptides and is applicable to various peptide sequences, potentially enabling the preparation of a library of Ψ[CH2 NH]-containing peptides.

Phenolic, lignin-derived substrates have emerged as desirable biorenewable chemical feedstocks for coupling reactions. A radical-mediated conversion of phenol derivatives to anilines is reported, using unfunctionalized hydroxamic acids as the N-centered radical source. The applicability of this triethyl phosphite mediated O-atom transfer approach, which tolerates a range of steric and electronic demands to naturally occurring phenols and lignin models, has been demonstrated in this work to access the corresponding aniline derivatives.

An ongoing challenge in trifluoromethylthiolation reactions is the use of less expensive and easily available trifluoromethylthio sources. Herein, we disclose an unprecedented usage of trifluoromethanesulfonic anhydride (Tf2 O) as a radical trifluoromethylthiolating reagent. Hydrotrifluoromethylthiolation of unactivated alkenes and alkynes with Tf2 O in the presence of PMePh2 and H2 O under visible-light photoredox catalysis gave the addition products. The trifluoromethylthio radical (. SCF3 ) was first formed from Tf2 O through a photoredox radical processes and deoxygenative reduction of PMePh2 , and H2 O serves as the H-atom donor for the hydrotrifluoromethylthiolation reaction. This reaction provides a new strategy for radical trifluoromethylthiolation.

BACKGROUND: Oils derived from plants, animal fats, and algae contain both saturated and unsaturated fatty acids. These fatty acids can be converted into liquid fuels and chemicals in the presence of active solid catalysts. RESULTS: Nickel‐based catalysts were supported on mordenite via ion exchange synthesis and evaluated for the deoxygenation of stearic acid to diesel fuels. By tuning the synthesis pH, loadings of over 20 wt% Ni were obtained. Catalysts synthesized at pH 8.5 displayed the highest Ni loading and the highest activity for the decarboxylation/decarbonylation of stearic acid under inert nitrogen gas atmospheres, yielding 47% heptadecane. Characterization included scanning transmission electron microscopy‐energy‐dispersive spectroscopy (STEM‐EDS), X‐ray diffraction (XRD), field emission scanning electron microscopy (FE‐SEM), inductively coupled plasma atomic emission spectroscopy (ICP‐AES), N₂ physisorption and thermogravimetric analysis (TGA), providing new insights into the recyclability of the catalyst. The observed loss of catalytic activity upon recycling was attributed to the agglomeration of Ni nanoparticles and the accumulation of carbonaceous coke. CONCLUSION: This work demonstrates that Ni‐based catalysts supported on mordenite zeolite can effectively convert stearic acid into heptadecane. Yields to heptadecane were as high as 47%. Mechanistically, the reaction proceeds by decarboxylation and decarbonylation pathways. © 2019 Society of Chemical Industry

The second case of linear end-on and evidence for an unprecedented bridging end-on coordination mode of CO2 have been discovered for vanadium aryloxide complexes of the tetradentate ligand system (ONNO)2- (ONNO=2,4-Me2 -2-(OH) C6 H2 CH2 ]2 N(CH2 )2 NMe2 ). The reaction of divalent (ONNO)VII (TMEDA) with CO2 and under the appropriate reaction conditions affords the trivalent (ONNO)VIII (OH)(η1 -CO2 ) resulting from an intermediate CO2 deoxygenation pathway followed by H-atom abstraction from the aromatic solvent, and CO2 fixation. In contrast, the reduction of trivalent (ONNO)VIII Cl(THF) with K, followed by exposure to CO2 in ethereal solvent, afforded the dinuclear [(ONNO)VII ]2 (μ, η1 -CO2 ).

An expansive NMR-based structural analysis of elusive glycosyl cations derived from natural and non-natural monosaccharides in superacids is disclosed. For the first time, it has been possible to explore the consequence of deoxygenation and halogen substitution at the C2 position in a series of 2-halogenoglucosyl, galactosyl, and mannosyl donors in the condensed phase. These cationic intermediates were characterized using low-temperature in situ NMR experiments supported by DFT calculations. The 2-bromo derivatives display intramolecular stabilization of the glycosyl cations. Introducing a strongly electron-withdrawing fluorine atom at C2 exerts considerable influence on the oxocarbenium ion reactivity. In a superacid, these oxocarbenium ions are quenched by weakly coordinating SbF6 - anions, thereby demonstrating their highly electrophilic character and their propensity to interact with poor nucleophiles.

BACKGROUND The application of riboflavin/UV-based pathogen inactivation (PI) to whole blood (WB) is currently limited by its negative impact on red blood cell (RBC) quality. The generation of reactive oxidative species in RBC products contributes to increased hemolysis. This study evaluated the impact of deoxygenation of WB prior to riboflavin/UV light treatment versus deoxygenation of RBC concentrates after PI treatment by monitoring RBC in vitro quality parameters. STUDY DESIGN AND METHODS Six ABO-matched WB units were pooled and split. Within three pairs, one unit was treated with riboflavin/UV light while the other was kept as an untreated control prior to manufacture into red cell concentrates (RCCs). The first pair (Cntr; Cntr-PI) served as the normoxic controls. Deoxygenation was performed at the RCC level for the second pair (RCCdeox; PI-RCCdeox), and at the WB level of the third pair (WBdeox; WBdeox-PI). In vitro qualities of the respective RBC units were assessed throughout storage. RESULTS The data for the Cntr and Cntr-PI units were comparable to previous reports. The PI-RCCdeox units exhibited worse in vitro quality for most parameters tested compared to Cntr-PI and WBdeox-PI units throughout storage. Hemolysis and microvesicle release was significantly (p

Lignin-rich digested stillage from second-generation bioethanol production is a unique biomass-derived feedstock, not only because it contains high amounts of lignin but also due to its residual amounts of cellulose and hemicellulose. In this study, catalytic hydrotreatment experiments were conducted on pyrolysis liquids obtained from the lignin-rich feedstock using sulphided NiMo/Al2O3 and CoMo/Al2O3 catalysts. The aim was to obtain a high conversion of the initial pyrolysis feed into a hydrotreated oil with a high phenolics and aromatics fractions. Experiments were carried out in a stirred batch reactor at 350 degrees C and 10 MPa of H-2 (initial pressure). Product oils were obtained in about 60-65% w/w, the remainder being an aqueous phase (12-14% w/w), solids (7-8% w/w) and gas phase components (all on initial pyrolysis oil feed basis). The product oils were characterised in detail using various techniques (elemental composition, GCxGC-FID, GPC, and 2D HSQC NMR). The oxygen content was reduced from 23% w/w in the pyrolysis oils to 7.5-11.5% in the hydrotreated oils, indicative of the occurrence of hydrodeoxygenation reactions. This was also evident from the chemical composition, showing an increase in the amounts of low molecular weight aromatics, alkylphenolics, alkanes and cycloalkanes in hydrotreated oils. Performance of the two catalysts was compared, and a higher degree of deoxygenation was observed for the NiMo catalyst. The implications of the findings for the valorisation of second-generation bioethanol residues are also discussed.

1,4-Bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadiene, 1, was tested as a reagent for the reductive silylation of various unsaturated functionalities, including N-heterocycles, quinones, and other redox-active moieties in addition to deoxygenation of main group oxides. Whereas most reactions tested are thermodynamically favorable, based on DFT calculations, a few do not occur, perhaps giving limited insight on the mechanism of this very attractive reductive process. Of note, reductive silylation reactions show a strong solvent dependence where a polar solvent facilitates conversions.