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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.)

Recently, it was shown that the double Ca-H-Ca-bridged calcium hydride cation dimer [LCaH 2 CaL] 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, CH 2 =CH 2 and H 2 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 H 2 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., (© 2022 The Authors. Published by Wiley-VCH GmbH.)

Methane (CH 4 ) is a sustainable carbon feedstock for value-added chemical production in aerobic CH 4 -oxidizing bacteria (methanotrophs). Under substrate-limited (e.g., oxygen and nitrogen) conditions, CH 4 oxidation results in the production of various short-chain organic acids and platform chemicals. These CH 4 -derived products could be broadened by utilizing them as feedstocks for heterotrophic bacteria. As a proof of concept, a two-stage system for CH 4 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 CH 4 and air supplementation schemes. CH 4 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 CH 4 (C-CH 4 ), 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-CH 4 . 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 C substrate -1 . However, further large-scale studies on fermenters and their optimization are required to increase the production yields of organic acids in methanotrophs., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Khanongnuch, Mangayil, Santala, Hestnes, Svenning and Rissanen.)

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 ( M w / M n ≈ 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., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

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.