Search

Recently, it was shown that the double Ca−H−Ca bridged calcium hydride cation dimer complex [LCaH2CaL]2+ (macrocyclic ligand L=NNNN‐tetradentate Me4TACD) exhibited remarkable activity in catalyzing the hydrogenation of unactivated 1‐alkenes as well as the H2 isotope exchange under mild conditions, tentatively via the terminal Ca−H bond of cation monomer LCaH+. In this DFT mechanistic work, a novel substrate‐dependent catalytic mechanism is disclosed involving cooperative Ca−H−Ca bridges for H2 isotope exchange, competitive Ca−H−Ca bridges and terminal Ca−H bonds for anti‐Markovnikov addition of unactivated 1‐alkenes, and terminal Ca−H bonds for Markovnikov addition of conjugation‐activated styrene. THF‐coordination plays a key role in favoring the anti‐Markovnikov addition while strong cation‐π interactions direct the Markovnikov addition to terminal Ca−H bonds. [ABSTRACT FROM AUTHOR]

Recently, it was shown that the double Ca−H−Ca‐bridged calcium hydride cation dimer [LCaH2CaL]2+ when stabilized by a larger macrocyclic N,N',N",N"',N""‐pentadentate ligand showed evidently higher activity than when stabilized by a smaller N,N',N",N"'‐tetradentate ligand in the catalytic hydrogenation of unactivated 1‐alkenes. In this DFT‐mechanistic work, the origin of the observed ring‐size effect is examined in detail using 1‐hexene, CH2=CH2 and H2 as substrates. It is shown that, at room temperature, both the N,N',N",N"',N""‐stabilized dimer and the monomer are not coordinated by THF in solution, while the corresponding N,N',N",N"'‐stabilized structures are coordinated by one THF molecule mimicking the fifth N‐coordination. Catalytic 1‐alkene hydrogenation may occur via anti‐Markovnikov addition over the terminal Ca−H bonds of transient monomers, followed by faster Ca−C bond hydrogenolysis. The higher catalytic activity of the larger N,N',N",N"',N""‐stabilized dimer is due to not only easier formation of but also due to the higher reactivity of the catalytic monomeric species. In contrast, despite unfavorable THF‐coordination in solution, the smaller N,N',N",N"'‐stabilized dimer shows a 3.2 kcal mol−1 lower barrier via a dinuclear cooperative Ca−H−Ca bridge for H2 isotope exchange than the large N,N',N",N"',N""‐stabilized dimer, mainly due to less steric hindrance. The observed ring‐size effect can be understood mainly by a subtle interplay of solvent, steric and cooperative effects that can be resolved in detail by state‐of‐the‐art quantum chemistry calculations. [ABSTRACT FROM AUTHOR]

Abstract Recently, it was shown that the double Ca−H−Ca‐bridged calcium hydride cation dimer [LCaH2CaL]2+ when stabilized by a larger macrocyclic N,N’,N’’,N’’’,N’’’’‐pentadentate ligand showed evidently higher activity than when stabilized by a smaller N,N’,N’’,N’’’‐tetradentate ligand in the catalytic hydrogenation of unactivated 1‐alkenes. In this DFT‐mechanistic work, the origin of the observed ring‐size effect is examined in detail using 1‐hexene, CH2=CH2 and H2 as substrates. It is shown that, at room temperature, both the N,N’,N’’,N’’’,N’’’’‐stabilized dimer and the monomer are not coordinated by THF in solution, while the corresponding N,N’,N’’,N’’’‐stabilized structures are coordinated by one THF molecule mimicking the fifth N‐coordination. Catalytic 1‐alkene hydrogenation may occur via anti‐Markovnikov addition over the terminal Ca−H bonds of transient monomers, followed by faster Ca−C bond hydrogenolysis. The higher catalytic activity of the larger N,N’,N’’,N’’’,N’’’’‐stabilized dimer is due to not only easier formation of but also due to the higher reactivity of the catalytic monomeric species. In contrast, despite unfavorable THF‐coordination in solution, the smaller N,N’,N’’,N’’’‐stabilized dimer shows a 3.2 kcal mol−1 lower barrier via a dinuclear cooperative Ca−H−Ca bridge for H2 isotope exchange than the large N,N’,N’’,N’’’,N’’’’‐stabilized dimer, mainly due to less steric hindrance. The observed ring‐size effect can be understood mainly by a subtle interplay of solvent, steric and cooperative effects that can be resolved in detail by state‐of‐the‐art quantum chemistry calculations.

Methane (CH4) is a sustainable carbon feedstock for value-added chemical production in aerobic CH4-oxidizing bacteria (methanotrophs). Under substrate-limited (e.g., oxygen and nitrogen) conditions, CH4 oxidation results in the production of various short-chain organic acids and platform chemicals. These CH4-derived products could be broadened by utilizing them as feedstocks for heterotrophic bacteria. As a proof of concept, a two-stage system for CH4 abatement and 1-alkene production was developed in this study. Type I and Type II methanotrophs, Methylobacter tundripaludum SV96 and Methylocystis rosea SV97, respectively, were investigated in batch tests under different CH4 and air supplementation schemes. CH4 oxidation under either microaerobic or aerobic conditions induced the production of formate, acetate, succinate, and malate in M. tundripaludum SV96, accounting for 4.8–7.0% of consumed carbon from CH4 (C-CH4), while M. rosea SV97 produced the same compounds except for malate, and with lower efficiency than M. tundripaludum SV96, accounting for 0.7–1.8% of consumed C-CH4. For the first time, this study demonstrated the use of organic acid-rich spent media of methanotrophs cultivating engineered Acinetobacter baylyi ADP1 ' tesA-undA cells for 1-alkene production. The highest yield of 1-undecene was obtained from the spent medium of M. tundripaludum SV96 at 68.9 ± 11.6 μmol mol Csubstrate–1. However, further large-scale studies on fermenters and their optimization are required to increase the production yields of organic acids in methanotrophs. [ABSTRACT FROM AUTHOR]

Methane (CH4) is a sustainable carbon feedstock for value-added chemical production in aerobic CH4-oxidizing bacteria (methanotrophs). Under substrate-limited (e.g., oxygen and nitrogen) conditions, CH4 oxidation results in the production of various short-chain organic acids and platform chemicals. These CH4-derived products could be broadened by utilizing them as feedstocks for heterotrophic bacteria. As a proof of concept, a two-stage system for CH4 abatement and 1-alkene production was developed in this study. Type I and Type II methanotrophs, Methylobacter tundripaludum SV96 and Methylocystis rosea SV97, respectively, were investigated in batch tests under different CH4 and air supplementation schemes. CH4 oxidation under either microaerobic or aerobic conditions induced the production of formate, acetate, succinate, and malate in M. tundripaludum SV96, accounting for 4.8–7.0% of consumed carbon from CH4 (C-CH4), while M. rosea SV97 produced the same compounds except for malate, and with lower efficiency than M. tundripaludum SV96, accounting for 0.7–1.8% of consumed C-CH4. For the first time, this study demonstrated the use of organic acid-rich spent media of methanotrophs cultivating engineered Acinetobacter baylyi ADP1 ‘tesA-undA cells for 1-alkene production. The highest yield of 1-undecene was obtained from the spent medium of M. tundripaludum SV96 at 68.9 ± 11.6 μmol mol Csubstrate–1. However, further large-scale studies on fermenters and their optimization are required to increase the production yields of organic acids in methanotrophs.

P450 fatty acid decarboxylases (FADCs) have recently been attracting considerable attention owing to their one‐step direct production of industrially important 1‐alkenes from biologically abundant feedstock free fatty acids under mild conditions. However, attempts to improve the catalytic activity of FADCs have met with little success. Protein engineering has been limited to selected residues and small mutant libraries due to lack of an effective high‐throughput screening (HTS) method. Here, we devise a catalase‐deficient Escherichia coli host strain and report an HTS approach based on colorimetric detection of H2O2‐consumption activity of FADCs. Directed evolution enabled by this method has led to effective identification for the first time of improved FADC variants for medium‐chain 1‐alkene production from both DNA shuffling and random mutagenesis libraries. Advantageously, this screening method can be extended to other enzymes that stoichiometrically utilize H2O2 as co‐substrate. [ABSTRACT FROM AUTHOR]

A comparative reactivity study of 1-alkene fuels from ethylene to 1-heptene has been performed using ignition delay time (IDT) measurements from both a high-pressure shock tube and a rapid compression machine, at an equivalence ratio of 1.0 in 'air', at a pressure of 30 atm in the temperature range of 600–1300 K. At low temperatures (< 950 K), the results show that 1-alkenes with longer carbon chains show higher fuel reactivity, with 1-pentene being the first fuel to show negative temperature coefficient (NTC) behavior followed by 1-hexene and 1-heptene. At high temperatures (> 950 K), the experimental results show that all of the fuels except propene show very similar fuel reactivity, with the IDTs of propene being approximately four times longer than for all of the other 1-alkenes. To analyze the experimental results, a chemistry mechanism has been developed using consistent rate constants for these alkenes. At 650 K, flux analyses show that hydroxyl radicals add to the double bond, followed by addition to molecular oxygen producing hydroxy‑alkylperoxy radicals, which can proceed via the Waddington mechanism or alternate internal H-atom isomerizations in chain branching similar to those for alkanes. We have found that the major chain propagation reaction pathways that compete with chain branching pathyways mainly produce hydroxyl rather than hydroperoxyl radicals, which explains the less pronounced NTC behavior for larger 1-alkenes compared to their corresponding alkanes. At 1200 K, flux analyses show that the accumulation of hydroperoxyl radicals is important for the auto-ignition of 1-alkenes from propene to 1-heptene. The rate of production of hydroperoxyl radicals for 1-alkenes from 1-butene to 1-heptene is higher than that for propene, which is due to the longer carbon chain facilitating hydroperoxyl radical formation via more efficient reaction pathways. This is the major reason that propene presents lower fuel reactivity than the other 1-alkenes at high temperatures. [ABSTRACT FROM AUTHOR]

Trace dimethoxymethane (DMM) was formed by aldol condensation of formaldehyde with methanol in industrial propene oxide production via a hydrogen peroxide (HPPO process). Probing the behaviour of catalytic action in oxidative cleavage reaction of C C bond of alkene is urgently needed for the development of production technology. Using 1-hexene as a probe, the oxidation of alkenes with H 2 O 2 was investigated via titanium silicalite-1 (TS-1) catalysis. Influences of solvent, temperature, additives and H 2 O 2 /alkene molar ratio on alkene conversion and oxidation product distribution were studied. Interestingly, besides the epoxidation products, aldehydes were also produced by double-bond oxidative cleavage in this system. The results showed that ethyl acetate as solvent was favor for the generation of aldehyde, but the additives [Na 2 HPO 4 ·12H 2 O (A) and NaH 2 PO 4 (B)] could significantly inhibit it. These phenomena indicated that the catalytic oxidative cleavage of 1-hexene in TS-1/H 2 O 2 system was probably based on an addition and cleavage oxidation process in an acidic environment. Unlabelled Image • Aldehydes were produced by C C oxidative cleavage of 1-alkenes in TS-1/H 2 O 2 system. • The addition of additives can greatly inhibit the C C oxidative cleavage reaction. • The C C cleavage reaction maybe based on an addition and cleavage oxidation process. [ABSTRACT FROM AUTHOR]

Homo- and copolymers of propylene and 1-decene were synthesized by controlled chain-walking (co)polymerization using phenyl substituted α-diimine nickel complexes activated with modified methylaluminoxane (MMAO). This catalytic system was found to polymerize propylene in a living fashion to furnish high molecular weight ethylene-propylene (EP) copolymers. The copolymerizations proceeded to give high molecular weight P/1-decene copolymers with narrow molecular weight distribution (Mw/Mn ≈ 1.2), which indicated a living nature of copolymerization at room temperature. The random copolymerization results indicated the possibility of precise branched structure control, depending on the polymerization temperature and time.

1-Alkenes are traditionally used as basic chemicals with great importance. Biosynthetic 1-alkenes also have the potential to serve as biofuels. In this study, we engineered a Pseudomonas lipolytic microbial platform for 1-alkene production using hydrophobic substrate as sole carbon source. Fatty acid decarboxylase UndA and UndB were cloned and expressed, which successfully produced 1-alkenes. Optimal culturing temperature and the interruption of competitive pathway were proven to be beneficial to 1-alkene synthesis. Chromosomal integration of UndB conferred 177.8 mg/L 1-alkenes (mainly 1-undecene) in lauric acid medium and 128.9 mg/L 1-alkenes (mainly 1-pentadecene) in palm oil medium. Thioesterase expression, adjustments of fatty acid degradation pathway and a second copy of UndB improved 1-alkene titer to 1102.6 mg/L using lauric acid and 778.4 mg/L using palm oil. All in all, this study offers the first demonstration of lipolytic microbial 1-alkene producing platform with highest reported 1-alkene product titer up to date. [ABSTRACT FROM AUTHOR]

• Global sensitivity analysis is utilized to build a skeletal oxidation mechanism for 1-hexene. • A set of skeletal oxidation mechanisms for C7–C14 1-alkenes is derived using reaction rate rules. • The effect of the C = C double bond is evaluated by BDE calculation and ROP analysis. • Satisfactory agreements between simulations and experiments are obtained for all test fuels. Olefins, accounting for one-fifth proportion of gasoline fuel, are also essential intermediates in the combustion of large hydrocarbons and vital precursors of large polycyclic aromatic hydrocarbons and soot. The unsaturated C = C bond of alkenes renders a more complex low-temperature reaction scheme compared with their corresponding n -alkanes. Thus, it is of great necessity to obtain a thorough knowledge of the chemical kinetics of alkenes. However, the studies on the chemical kinetics of long-chain olefins are far from sufficient. In this work, a collection of skeletal oxidation mechanisms for 1-alkenes from 1-hexene (C 6 H 12 -1) to 1-tetradecene (C 14 H 28 -1) were constructed in light of recent advances in skeletal mechanism construction for fuels sharing similar structures based on reaction rate rules. For each 1-alkene, the skeletal mechanism includes ∼54 species and ∼216 reactions. Meanwhile, the effect of the C = C double bond was evaluated by conducting a bond dissociation energy calculation to assist the skeletal mechanism construction and derivation. It is discovered that the allylic position is preferred for H-atom abstraction reactions owing to its lowest bond dissociation energy among different locations for all heavy 1-alkenes. Furthermore, the reactions of OH addition to the C = C bond become important at low temperatures, which competes with the H-atom abstraction reactions. This results in the lower reactivity of 1-alkenes compared with corresponding n -alkanes at low temperatures. The acquired skeletal mechanisms were validated against extensive experimental data including laminar flame speeds, ignition delay times in shock tubes, and key species concentrations in jet-stirred reactors, flow reactors, and premixed laminar flames. The good agreements between experiments and simulations demonstrate the prediction capability of all the skeletal mechanisms of 1-alkenes although minor discrepancies exist in the concentration predictions for C 2 –C 3 species, which might stem from a highly reduced C 2 –C 3 sub-mechanism being utilized in the present mechanism. [ABSTRACT FROM AUTHOR]

A series of α-diimine Ni(II) complexes containing bulky phenyl groups, [ArN = C(Naphth)C = NAr]NiBr2 (Naphth: 1,8-naphthdiyl, Ar = 2,6-Me2-4-PhC6H2 (C1); Ar = 2,4-Me2-6-PhC6H2 (C2); Ar = 2-Me-4,6-Ph2C6H2 (C3); Ar = 4-Me-2,6-Ph2C6H2 (C4); Ar = 4-Me-2-PhC6H3 (C5); Ar = 2,4,6-Ph3C6H2 (C6)), were synthesized and characterized. Upon activation with either diethylaluminum chloride (Et2AlCl) or modified methylaluminoxane (MMAO), all Ni(II) complexes showed high activities in ethylene polymerization and produced highly branched amorphous polyethylene (up to 145 branches/1000 carbons). Interestingly, the sec-butyl branches were observed in polyethylene depending on polymerization temperature. Polymerization of 1-alkene (1-hexene, 1-octene, 1-decene and 1-hexadecene) with C1-MMAO at room temperature resulted in branched polyolefins with narrow Mw/Mn values (ca. 1.2), which suggested a living polymerization. The polymerization results indicated the possibility of precise microstructure control, depending on the polymerization temperature and types of monomers. [ABSTRACT FROM AUTHOR]

Recently, it was shown that the double Ca-H-Ca bridged calcium hydride cation dimer complex [LCaH 2 CaL] 2+ (macrocyclic ligand L=NNNN-tetradentate Me 4 TACD) exhibited remarkable activity in catalyzing the hydrogenation of unactivated 1-alkenes as well as the H 2 isotope exchange under mild conditions, tentatively via the terminal Ca-H bond of cation monomer LCaH + . In this DFT mechanistic work, a novel substrate-dependent catalytic mechanism is disclosed involving cooperative Ca-H-Ca bridges for H 2 isotope exchange, competitive Ca-H-Ca bridges and terminal Ca-H bonds for anti-Markovnikov addition of unactivated 1-alkenes, and terminal Ca-H bonds for Markovnikov addition of conjugation-activated styrene. THF-coordination plays a key role in favoring the anti-Markovnikov addition while strong cation-π interactions direct the Markovnikov addition to terminal Ca-H bonds., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Die enzymatische oxidative Decarboxylierung von linearen kurzkettigen Fettsäuren (C4:0-C9:0) unter Verwendung der P450-Monooxygenase OleT, O2 und NAD(P)H als Elektronendonor ermöglicht die Synthese terminaler C3- bis C8-Alkene mit Produkttitern von bis zu 0.93 g L−1 und TTNs >2000. Essentiell für diesen Prozess war die Entwicklung einer effizienten Elektronentransferkette unter Verwendung von Putidaredoxin (CamAB) und NAD(P)H-Regeneration basierend auf Glukose, Ameisensäure oder Phosphonat. Mithilfe dieses Reaktionssystems lassen sich auf biokatalytischem Weg industriell wichtige Alkene, wie z. B. Propen und 1-Octen zum ersten Mal vollständig aus nachwachsenden Rohstoffen herstellen. [ABSTRACT FROM AUTHOR]

We report the results of a joint theoretical and experimental investigation into the copolymerisation of acrylamides and acrylates with α-olefins in free-radical processes. The transition-state structures of models for free-radical homo- and copolymerisation involving acrylamide, methylacrylamide, methacrylate, methyl methacrylate, and ethylene have been determined using density functional theory. The reaction energies and barrier heights comport with the experimentally observed properties, including the prevalence of monomer alternation, the realised stereospecificity, and the reaction yield. Continuum solvation models have been applied to determine the sensitivity of the relative energies to the bulk solvent properties. Experimentally, a Lewis acid catalyst is demonstrated to increase the incorporation of nonpolar 1-alkenes in copolymerisations with polar acrylamides and acrylates. In the presence of the Lewis acid, scandium (III) trifluoromethanesulfonate, the copolymerisation of 1-hexene and acrylamide results in an 8.5 mol % incorporation, up from 3.9 mol % in the absence of the Lewis acid. Computations incorporating Mg2+as a model Lewis acid elucidate the mechanism of this catalysis. In the addition of methacrylate to a methyl methacrylate radical terminated polymer, the Lewis acid binds to the carbonyls on both promoting isotactic addition, while for the addition of an alkene to the same polymer, the Lewis acid binds to the polymer, reducing the barrier for alkenyl addition inductively by withdrawing electron density. We have demonstrated the ability of computational studies to aid experimentalists in the synthesis of new copolymers with desired properties. [ABSTRACT FROM PUBLISHER]

Abstract: Excess molar volumes V E measured at 288.15 and 308.15K for (1-hexanol+1-hexene), (1-hexanol+1-octene) and (1-hexanol+1-decene) systems are reported. The data and the measurements reported before at 298.15K for this series of mixtures were used to estimate the excess molar isobaric thermal expansion and the partial molar excess isobaric thermal expansions of the components at 298.15K. The as a function of concentration, changes from positive–negative for the systems formed by short-chain 1-alkenes like 1-hexene to positive for 1-decene over the whole concentration range. The modified Treszczanowicz and Benson model (TB) is applied to interpret and to predict changes in the size and shape of the and curves. The model predicts qualitatively well the changes of the and values in the series of mixtures as a superposition of the contributions due to self-association of alkanol, free volume, OH⋯π interactions and residual van der Waals interactions. These contributions to the properties investigated are estimated and discussed in the series of mixtures. The results obtained are compared with those for 1-alkanol+ n-alkane systems. [Copyright &y& Elsevier]

Abstract: This review describes thermal decomposition studies that have been carried out on metallacycloalkane compounds, and also includes discussion on reaction mechanisms. The decomposition pathways for these compounds are strongly dependent on the nature of the metal, the ligand system, as well as solvent and temperature. The organic product distribution on the decomposition of metallacycloalkanes is also discussed. [Copyright &y& Elsevier]

Homo- and copolymers of propylene and 1-decene were synthesized by controlled chain-walking (co)polymerization using phenyl substituted α-diimine nickel complexes activated with modified methylaluminoxane (MMAO). This catalytic system was found to polymerize propylene in a living fashion to furnish high molecular weight ethylene-propylene (EP) copolymers. The copolymerizations proceeded to give high molecular weight P/1-decene copolymers with narrow molecular weight distribution (Mw/Mn ≈ 1.2), which indicated a living nature of copolymerization at room temperature. The random copolymerization results indicated the possibility of precise branched structure control, depending on the polymerization temperature and time. [ABSTRACT FROM AUTHOR]

A series of α-diimine Ni(II) complexes containing bulky phenyl groups, [ArN = C(Naphth)C = NAr]NiBr₂ (Naphth: 1,8-naphthdiyl, Ar = 2,6-Me₂-4-PhC₆H₂ (C1); Ar = 2,4-Me₂-6-PhC₆H₂ (C2); Ar = 2-Me-4,6-Ph₂C₆H₂ (C3); Ar = 4-Me-2,6-Ph₂C₆H₂ (C4); Ar = 4-Me-2-PhC₆H₃ (C5); Ar = 2,4,6-Ph₃C₆H₂ (C6)), were synthesized and characterized. Upon activation with either diethylaluminum chloride (Et₂AlCl) or modified methylaluminoxane (MMAO), all Ni(II) complexes showed high activities in ethylene polymerization and produced highly branched amorphous polyethylene (up to 145 branches/1000 carbons). Interestingly, the sec- butyl branches were observed in polyethylene depending on polymerization temperature. Polymerization of 1-alkene (1-hexene, 1-octene, 1-decene and 1-hexadecene) with C1-MMAO at room temperature resulted in branched polyolefins with narrow M w / M n values ( ca. 1.2), which suggested a living polymerization. The polymerization results indicated the possibility of precise microstructure control, depending on the polymerization temperature and types of monomers.