Oxidative Decarbonylation Research Articles

Inclusion complexes of cucurbit[n]urils (n = 7, 8) with η5‐cyclopentadienyl methyl tricarbonyl molybdenum(II) and their use in epoxidation catalysis

There are very few known examples of supramolecular compounds comprising molybdenum species hosted inside the portals/cavities of cucurbit[n]urils (CBn). In this work, CB7 and CB8 macrocycles have been studied as hosts for the carbonyl complex [CpMo(CO)3Me] (1) (Cp = η5‐C5H5). Compounds were isolated in the solid state and characterized as genuine 1:1 inclusion complexes (1@CBn) by elemental and thermogravimetric analyses, powder X‐ray diffraction, scanning electron microscopy, 13C{1H} cross‐polarization magic‐angle spinning NMR, FT‐IR, Raman, and diffuse reflectance UV–Vis spectroscopies. The host–guest structures can act as supramolecular precatalysts for olefin epoxidation. Based on the model reaction of cis‐cyclooctene with hydroperoxide oxidants (tert‐butylhydroperoxide or hydrogen peroxide), the structural features of 1@CBn as well as the operating conditions influence the catalytic process. The metal species in 1@CBn undergo oxidative decarbonylation in situ, giving oxidized metal species that are catalytically active for olefin epoxidation. The type of oxidant and solvent influences the catalytic activity and stability. 1@CB8 was more stable than 1@CB7 with regard to catalyst recycling and reuse. Based on the substrate scope investigation, for relatively large olefins, such as the fatty acid methyl ester methyl oleate, the size of the macrocyclic host may be a determining factor for catalytic activity.

Oxidative Decarbonylation of an Azacalixpyridine-Supported Mo(0)-Tricarbonyl to a Mo(VI)-Trioxo Complex with Dioxygen in Solution and on Au(111): Determination of Molecular Mechanism.

The conversion of an azacalixpyridine-supported Mo(0) tricarbonyl into a Mo(VI) trioxo complex with dioxygen (O2) is investigated in homogeneous solution and in a molecular film adsorbed on Au(111) using a variety of spectroscopic and analytical methods. These studies in particular show that the dome-shaped carbonyl complex adsorbed on the metal surface has the ability to bind and activate gaseous oxygen, overcoming the so-called surface trans-effect. Furthermore, the rate of the conversion dramatically increases by irradiation with light. This observation is explained with the help of complementary DFT calculations and attributed to two different pathways, a thermal and a photochemical one. Based on the experimental and theoretical findings, a molecular mechanism for the conversion of the carbonyl to the oxo complex is derived.

Diiron azadithiolate models with bulky bridgehead moiety: Synthesis, structure and electrochemistry

To further explore the function of azadithiolate (ADT) bridges in diiron complexes and to develop new biomimics for the active site of [FeFe]-H2ases, here a new model complex [Fe2{(μ-SCH2)2NCHPh2}(CO)6] (1), featuring a bulky bridgehead (CHPh2) was prepared by condensation reaction of [Fe2(μ-SCH2OH)2(CO)6] and NH2CHPh2. The corresponding monophosphine-substituted diiron azadithiolate complexes, [Fe2{(μ-SCH2)2NCHPh2}(CO)5 L] (2–7) [L = PPh3, PPh2(2-C5H4N), PPh2(C6H11), P(C6H4–4-CH3)3, P(C6H4–4–OCH3)3, P(2-C4H3O)3], were prepared via the one-pot method that involves [Fe2(μ-SCH2OH)2(CO)6], phosphine ligand and NH2CHPh2. The diphosphine-substituted complexes, [Fe2{(μ-SCH2)2NCHPh2}(CO)5(κ1-dppm)] [dppm = CH2(PPh2)2] (8), [Fe2{(μ-SCH2)2NCHPh2} (CO)4{(κ2-Ph2P)2NCH2C6H5}] (9), [Fe2{(μ-SCH2)2NCHPh2}(CO)4(μ-dppm)] (10) and [Fe2{(μ-SCH2)2NCHPh2}(CO)4{(μ-Ph2P)2NCH2Ph}] (11) were synthesized using either Me3NO-assisted oxidative decarbonylation reaction or thermal reaction. All the new complexes were fully structurally characterized by elemental analysis, spectroscopies, and particularly for 2–10 by X-ray crystallography. Furthermore, the electrochemical and electrocatalytic properties of these model complexes were investigated by cyclic voltammetry, demonstrating their ability to catalyze the reduction of protons to produce H2 when acetic acid was used as the proton source.

A synthetic cycle for iminophosphorane synthesis involving direct intermolecular NP bond formation on N2-derived molybdenum nitride.

NP bonds were built straightforwardly between N2-derived molybdenum terminal nitride and phosphines. Subsequent PCET, oxidative decarbonylation and then reduction regenerated the N2 complex, developing a synthetic cycle transferring N2 into various iminophosphoranes. Both aryl and alkyl substituted phosphines proceeded smoothly.

Kinetics-Based Quantification of Peroxynitrite Using the Oxidative Decarbonylation of Isatin.

Peroxynitrite and its radical decomposition products are highly reactive nitrogen and oxygen species that can influence the balance between health and disease in multiple organ systems. Despite vigorous research activity, real-time quantitative monitoring of peroxynitrite generated by donor compounds remains challenging. Here, we report a kinetics-based fluorescence method for quantitative tracking of peroxynitrite generation using the oxidative decarbonylation of isatin to form anthranilic acid as a fluorescent probe. This method relies on knowledge of the rate of the reaction of peroxynitrite with the probe, which we measure using stopped-flow fluorescence techniques. To the best of our knowledge, this is the first optical method capable of providing real-time quantitative measures of peroxynitrite concentrations generated from donor compounds, as demonstrated herein for SIN-1 and Angeli's salt.

Pd-Promoted Cyclization of (Z)-Pent-2-en-4-yn-1-yl Alkanoates Leading to Furans via an Acyl Group Shift and Further Synthetic Transformation.

Palladium-promoted acyl migration was observed in the reaction of (Z)-pent-2-en-4-yn-1-yl alkanoates in the presence of DBU to yield 2-(alkanoylmethyl)furan derivatives (2) in high yields. Compounds 2 then underwent oxidative decarbonylation to afford 2-acylfurans with O2 as the oxidant under mild and metal-free conditions. The mechanistic pathway of the reaction involving an intramolecular cyclization and acyl group shift is discussed.

Expeditious Synthesis of Fluorescent Bis(phenylfuryl)benzenes

AbstractVersatile fluorescent polyaromatic compounds of alternating benzene and furan rings, para- and meta-bis(5-phenylfur-3-yl)benzenes, were expeditiously synthesized by double Mn(OAc)3-catalyzed oxidative decarbonylation and Paal–Knorr reactions of β-ketoesters, prepared from the conjugate addition of ethyl acetoacetate to para- and meta-bis(chalcones). Stronger fluorescence intensity was observed for meta-bis(phenylfuryl)benzene with ortho-methoxy substitution, whereas longer fluorescence wavelength was observed for para-bis(phenylfuryl)benzene with para-methoxy substitution.

Exploring replacement of axially coordinated ligands in ruthenium(II) phthalocyaninates

We report an extensive study of axial ligand replacement in ruthenium(II) complexes with tetra-tert-butyl-phthalocyanine (tBu4Pc). For this purpose oxidative decarbonylation of [tBu4PcRu](CO) in the presence of trimethylamine was performed providing [tBu4PcRu](NMe3)2 complex in 92% yield. Its heating with pyrazine in o-dichlorobenzene at 100 °C gave [tBu4PcRu](Pyz)2 in quantitative yield. A simplified TD-DFT approximation has been used to explain the difference in the appearance of UV–Vis spectra of synthesized complexes with different N-donor ligands in terms of π-π* or charge transfer excitations, assignment was validated by the studies of solvatochromism of synthesized complexes. The reported finding can pave a convenient way to a relatively mild selective synthesis of ruthenium phthalocyaninates carrying N-donor aromatic ligands. Such complexes attract interest for various photo- and electroactive applications, catalysis and medicine.

A CYP380C10 gene is required for waterproofing and water retention in the insect integument

Cuticular hydrocarbons (CHCs) are important components in the integument of insects and are required for development and survival. Insect-specific CYP4G subfamily, of the P450 enzymes, catalyze the oxidative decarbonylation step in the biosynthesis of CHCs. Here, we characterized CYP380C10 gene function in a Hemiptera rice pest, Nilaparvata lugens. We used RNA interference–mediated expression silencing to reveal that NlCYP380C10 played a key role in waterproofing and water–retention in the integument of N. lugens. Knockdown of NlCYP380C10 significantly reduced body weight and caused mortality. Scanning electron microscopy showed the loss of the lipid layer on the surface of the abdominal cuticle of the dsNlCYP380C10-injected adults. Furthermore, CHC profile analysis revealed that NlCYP380C10 knockdown significantly decreased the amounts of CHCs in adult females. This suggested that NlCYP380C10 was involved in CHC biosynthesis. Reduction of CHC content caused the loss of the intact lipid layer of the cuticle, which resulted in loss of the waterproofing and water-retention functions. This led to failure of molting and eclosion. Our findings expanded the knowledge of CHC biosynthesis in the insect integument and led to a better understanding of the functional roles of CYP450 genes involved in waterproofing and water–retention in insects.

Assembly of functionalized π-extended indolizine polycycles through dearomative [3+2] cycloaddition/oxidative decarbonylation.

Reported herein is an unexpected construction of functionalized π-extended indolizine polycycles through a one-pot two-step cascade process comprising the base-promoted dearomative [3+2] cycloaddition of quinilinium salts and 3-alkenyl oxindoles, followed by a DDQ-mediated oxidative decarbonylation. Moreover, we could achieve the substrate-controlled diverse synthesis of structurally strained cyclopropane spirooxindole by using pyridinium salts as starting materials.

A long-wavelength turn-on fluorescent probe for intracellular nanomolar level peroxynitrite sensing with second-level response

As a typical kind of endogenous reactive nitrogen species, peroxynitrite (ONOO−) is believed heavily involved in the pathogenesis of many diseases such as inflammation, neurodegenerative conditions, and cardiovascular disorders. Precisely estimating ONOO− level in cell compartments is crucial for unraveling the biological relevance of ONOO− and enabling effective control of ONOO−-associated pathogenicity but suffers from serious difficulty owing to the daunting elusive features of ONOO−, namely nanomolar level physiological concentration and millisecond level biological half-life. A new fluorescent probe capable of detecting ONOO− with limit of detection down to 1.2 nM, response time less than 1s, and high recognition specificity over other similarly interfering species was developed in this work. For the probe constructed by conjugating an isatin moiety with an electron-withdrawing tricyanofuran (TCF) moiety, the former enabled a highly selective ONOO−-mediated oxidative decarbonylation reaction while the latter significantly improved the electrophilicity of the 3-position carbonyl group of isatin moiety and therefore accelerate the ONOO−-mediated nucleophilic attack, which eventually enabled prompt and efficient recognition reaction. For the decarbonylated product featured with a released primary aniline moiety, TCF acted as an acceptor for enabling an intramolecular charge transfer (ICT) process and the remarkable change in electronic feature upon reaction with ONOO−, which generated turn-on fluorescence with large contrast and therefore the basis for ONOO− sensing. The cell fluorescence imaging performed in this work definitely verified the capability of the probe for mapping intracellular ONOO−, despite the daunting elusive features of such physiological species.

TBHP/TBAI–Mediated simple and efficient synthesis of 3,5-disubstituted and 1,3,5-trisubstituted 1H-1,2,4-triazoles via oxidative decarbonylation of aromatic aldehydes and testing for antibacterial activities

The author has developed a simple, efficient and eco–friendly convenient general method for synthesis of 3,5–disubstituted–1,2,4–triazoles and 1,3,5–trisubstituted–1,2,4–triazoles from 3–monosubstituted–1,2,4–triazoles and 1,3–disubstituted–1,2,4–triazoles respectively using tetrabutylammonium iodide (TBAI) as catalyst and TBHP as oxidant under mid reaction conditions. This method provides structurally diverse 3,5–disubstituted 1,2,4–triazoes and 1,3,5––trisubstituted–1,2,4–triazoles in good to excellent yields. 3,5–Disubstituted 1,2,4–triazoes and 1,3,5––trisubstituted–1,2,4–triazoles derivatives are biologically and pharmaceutically active molecules, and therefore, this protocol could be of wide applications in medicinal chemistry and organic chemistry.

Two functionally distinct CYP4G genes of Anopheles gambiae contribute to cuticular hydrocarbon biosynthesis

Cuticular hydrocarbon (CHC) biosynthesis is a major pathway of insect physiology. In Drosophila melanogaster the cytochrome P450 CYP4G1 catalyses the insect-specific oxidative decarbonylation step, while in the malaria vector Anopheles gambiae, two CYP4G paralogues, CYP4G16 and CYP4G17 are present. Analysis of the subcellular localization of CYP4G17 and CYP4G16 in larval and pupal stages revealed that CYP4G16 preserves its PM localization across developmental stages analyzed; however CYPG17 is differentially localized in two distinct types of pupal oenocytes, presumably oenocytes of larval and adult developmental specificity. Western blot analysis showed the presence of two CYP4G17 forms, potentially associated with each oenocyte type. Both An. gambiae CYP4Gs were expressed in D. melanogaster flies in a Cyp4g1 silenced background in order to functionally characterize them in vivo. CYP4G16, CYP4G17 or their combination rescued the lethal phenotype of Cyp4g1-knock down flies, demonstrating that CYP4G17 is also a functional decarbonylase, albeit of somewhat lower efficiency than CYP4G16 in Drosophila. Flies expressing mosquito CYP4G16 and/or CYP4G17 produced similar CHC profiles to ‘wild-type’ flies expressing the endogenous CYP4G1, but they also produce very long-chain dimethyl-branched CHCs not detectable in wild type flies, suggesting that the specificity of the CYP4G enzymes contributes to determine the complexity of the CHC blend. In conclusion, both An. gambiae CYP4G enzymes contribute to the unique Anopheles CHC profile, which has been associated to defense, adult desiccation tolerance, insecticide penetration rate and chemical communication.

Mn(II)-Catalyzed C-H Alkylation of Imidazopyridines and N-Heteroarenes via Decarbonylative and Cross-Dehydrogenative Coupling.

A Mn(II)-catalyzed efficient C-H alkylation of imidazoheterocycles and N-heteroarenes with aliphatic aldehydes has been developed via oxidative decarbonylation. Other alkylating agents such as cyclic alkanes, ethers, and alcohols also coupled with N-heteroarenes through cross-dehydrogenative coupling. Regioselectively C5-alkylated imidazoheterocycles were synthesized in good yields. Experimental results show that radical pathway might be involved in this reaction.

Mountain pine beetle (Dendroctonus ponderosae) CYP4Gs convert long and short chain alcohols and aldehydes to hydrocarbons

Hydrocarbon biosynthesis in insects involves the elongation of fatty acyl-CoAs to very-long chain fatty acyl-CoAs that are then reduced and converted to hydrocarbon, with the last step involving the oxidative decarbonylation of an aldehyde to hydrocarbon and carbon dioxide. Cytochromes P450 in the 4G family decarbonylate aldehydes to hydrocarbon. All insect acyl-CoA reductases studied to date reduce fatty acyl-CoAs to alcohols. The results of the work reported herein demonstrate that CYP4G55 and CYP4G56 from the mountain pine beetle, Dendroctonus ponderosae, expressed as fusion proteins with house fly cytochrome P450 reductase (CPR), convert both long chain aldehydes and long chain alcohols to hydrocarbons. CYP4G55 and CYP4G56 appear to prefer primary alcohols to aldehydes as substrates. These data strongly suggest that hydrocarbon biosynthesis in insects occurs by the two-step reduction of very long chain fatty acyl-CoAs to alcohols, which are then oxidized to aldehydes and then oxidatively decarbonylated to hydrocarbon by CYP4G enzymes. In addition, both CYP4G55 and CYP4G56 fusion proteins convert C10 alcohols and aldehydes to hydrocarbons, including the conversion of (Z)-7-decenal, a putative intermediate in the exo-brevicomin pheromone biosynthetic pathway, to (Z)-3-nonene. These data demonstrate that the highly conserved CYP4G enzymes accept a broad range of carbon chain lengths, including C10 and C18, and have evolved to function in cuticular hydrocarbon biosynthesis and pheromone production.

A chemiluminescent probe for cellular peroxynitrite using a self-immolative oxidative decarbonylation reaction.

Peroxynitrite (ONOO-) is a highly reactive oxygen species which has been recognized as an endogenous mediator of physiological activities like the immune response as well as a damaging agent of oxidative stress under pathological conditions. While its biological importance is becoming clearer, many of the details of its production and mechanism of action remain elusive due to the lack of available selective and sensitive detection methods. Herein, we report the development, characterization, and biological applications of a reaction-based chemiluminescent probe for ONOO- detection, termed as PNCL. PNCL reacts with ONOO-via an isatin moiety through an oxidative decarbonylation reaction to initiate light emission that can be observed instantly with high selectivity against other reactive sulphur, oxygen, and nitrogen species. Detailed studies were performed to study the reaction between isatin and ONOO-, which confirm selectivity for ONOO- over NO2˙. PNCL has been applied for ONOO- detection in aqueous solution and live cells. Moreover, PNCL can be employed to detect cellular ONOO- generated in macrophages stimulated to mount an immune response with lipopolysaccharide (LPS). The sensitivity granted by chemiluminescent detection together with the specificity of the oxidative decarbonylation reaction provides a useful tool to explore ONOO- chemistry and biology.

Molybdenum(0) tricarbonyl and tetracarbonyl complexes with a cationic pyrazolylpyridine ligand: synthesis, crystal structures and catalytic performance in olefin epoxidation.

The synthesis of molybdenum(0) tricarbonyl and tetracarbonyl complexes of the form [Mo(CO)3(ptapzpy)Br] (1) and cis-[Mo(CO)4(ptapzpy)]Br (2) is reported, where ptapzpy = 2-(1-propyltrimethylammonium-3-pyrazolyl)pyridine. Preparation of these derivatives was accomplished either through thermal replacement of CO in Mo(CO)6 (for 1) or substitution under milder conditions of piperidine ligands in the precursor cis-[Mo(CO)4(pip)2] (for 2). The crystal structures of the ligand [ptapzpy]Br and complexes 1 and 2 were determined. Thermal treatment of 2 at 125–150 °C leads to mono decarbonylation and formation of 1. On the other hand, oxidative decarbonylation of 1 and 2 by reaction with tert-butylhydroperoxide (TBHP, 10 equiv.) gives a molybdenum oxide hybrid material formulated as [Mo3O9([ptapzpy]Br)2]·nH2O (3), which was characterised by FT-IR and Raman spectroscopy, thermogravimetric analysis, and 13C{1H} CP MAS NMR spectroscopy. Compounds 1–3 were effective (pre)catalysts for the epoxidation of cis-cyclooctene at 55 °C with aqueous H2O2 or TBHP (slightly better results were obtained with the former). The characterisation of the Mo-containing solids isolated after the catalytic reaction showed that poorly soluble β-octamolybdate salts, (L)x[Mo8O26], were formed from 1–3 with TBHP and from 1 with H2O2, while soluble oxoperoxo species were formed from 3 with H2O2. These findings helped to explain the different catalytic performances obtained.

Aminophosphine-substituted diiron dithiolate complexes: Synthesis, crystal structure, and electrocatalytic investigation

As the active site models of [FeFe]-hydrogenases, two new aminophosphine-monosubstituted diiron dithiolate compelxes with the general formulae Fe2(μ-pdt)(CO)5{PPh2NH(C6H4R-p)} (pdt = SCH2CH2CH2S; R = Br (1), Me (2)), were prepared by the oxidative decarbonylation of parent Fe2(μ-pdt)(CO)6 (A) with monophosphines Ph2PNH(C6H4Br-p) or Ph2PNH(C6H4Me-p) in the presence of decarbonylating agent Me3NO·2H2O in MeCN. Interestingly, the ambient temperature treatment of A and aminodiphosphine Ph2PN(C6H4Me-p)PPh2 resulted in the formation of the major chelated complex Fe2(μ-pdt)(CO)4{κ2-Ph2PN(C6H4Me-p)PPh2} (3) concomitant with the minor complex 2. All the complexes 1-3 have been well characterized by elemental analysis, FTIR, NMR (1H, 31P) spectroscopies, and X-ray crystallography. Additionally, the electrochemical and electrocatalytic properties of complexes 1-3 are studied using cyclic voltammetry, where the ratios of the catalytic current (icat) to the reductive peak current (ip) for similar complexes 1, 2, and parent A at 10 mM HOAc exhibit a ranking of 2 ≈ 1 > A.

Synthesis of Cyclopentadienyl-Based Trioxo-rhenium Complexes and Their Use as Deoxydehydration Catalysts

The cyclopentadienyl-based trioxo-rhenium complexes CptttReO3 (Cpttt = 1,2,4-tritert-butylcyclopentadienyl) 1b and Cp*ReO3 (Cp* = pentamethylcyclopentadienyl) 4b) are known to be active catalysts for the deoxydehydration (DODH) of vicinal diols to olefins. Here, we report on the preparation of a series of complexes of the general formula Cp′ReO3 (Cp′ = 1,3-di-tert-butylcyclopentadienyl (Cptt, 2b, 18%), 1,2,3-triisopropylcyclopentadienyl (3b, 4%), 1,2,3-trimethyl-4,5,6,7-tetrahydroindenyl (6b, 36%), and tetramethylcyclopentadienyl (7b, 33%)) in which the electronic and steric properties of the Cp′ ligand are varied. These complexes were synthesized via oxidative decarbonylation from the corresponding Cp′Re(CO)3 complexes with either H2O2 or tBuOOH. An in situ NMR investigation revealed that complexes 2b, 3b, and 6b are unstable under the oxidizing reaction conditions. This information was used to determine the optimal reaction time to isolate the complexes 2b, 3b, and 6b. These “piano-stool” configurated C...

Sequential Construction Strategy for Rational Design of Luminescent Iridacycles

A convenient and general strategy has been developed to synthesize stable iridapolycycles 5–8. Reaction of arylacetylenes with iridium-hydride complex [IrH(CO)Cl(PPh3)3]BF4 via nucleophilic addition, oxidative decarbonylation, and C–H bond activation results in the formation of a series of iridacyclopentadiene derivatives, including benzo-iridacyclopentadiene 5, naphtho-iridacyclopentadiene 6, pyreno-iridacyclopentadiene 7, and thieno-iridacyclopentadiene 8. These iridapolycycles display high thermal and air stability yet can be further functionalized via facile ligand substitution reactions. As an example, complex 5 was used as a metallosynthon to react with 2,2′-dipyridyl to give intensely luminescent Ir(III) complex 9 bearing one C∧C and one N∧N ligands. Density functional theory (DFT) calculations reveal that the lowest unoccupied molecular orbitals (LUMOs) of iridapolycycles 5–8 are located on the phosphonium groups while the highest occupied molecular orbitals (HOMOs) are mainly located on the metal...