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1. Activator-free single-component Co( i )-catalysts for regio- and enantioselective heterodimerization and hydroacylation reactions of 1,3-dienes. New reduction procedures for synthesis of [L]Co( i )-complexes and comparison to in situ generated catalysts

   https://doi.org/10.1039/d2dt01484j  

   Parsutkar, Mahesh M.; Moore, Curtis E.; RajanBabu, T. V. (June 2022, Dalton Transactions)

   Warren Piers (Ed.)

   Although cobalt( i ) bis-phosphine complexes have been implicated in many selective C–C bond-forming reactions, until recently relatively few of these compounds have been fully characterized or have been shown to be intermediates in catalytic reactions. In this paper we present a new practical method for the synthesis and isolation of several cobalt( i )-bis-phosphine complexes and their use in Co( i )-catalyzed reactions. We find that easily prepared ( in situ generated or isolated) bis-phosphine and (2,6- N -aryliminoethyl)pyridine (PDI) cobalt( ii ) halide complexes are readily reduced by 1,4-bis-trimethylsilyl-1,4-dihydropyrazine or commercially available lithium nitride (Li 3 N), leaving behind only innocuous volatile byproducts. Depending on the structures of the bis-phosphines, the cobalt( i ) complex crystallizes as a phosphine-bridged species [(P∼P)(X)Co I [μ-(P∼P)]Co I (X)(P∼P)] or a halide-bridged species [(P∼P)Co I [μ-(X)] 2 Co I (P∼P)]. Because the side-products are innocuous, these methods can be used for the in situ generation of catalytically competent Co( i ) complexes for a variety of low-valent cobalt-catalyzed reactions of even sensitive substrates. These complexes are also useful for the synthesis of rare cationic [(P∼P)Co I -η 4 -diene] + X − or [(P∼P)Co I -η 6 -arene] + X − complexes, which are shown to be excellent single-component catalysts for the following regioselective reactions of dienes: heterodimerizations with ethylene or methyl acrylate, hydroacylation and hydroboration. The reactivity of the single-component catalysts with the in situ generated species are also documented. 

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2. Tellurorhodamine photocatalyzed aerobic oxidation of organo-silanes and phosphines by visible-light

   https://doi.org/10.1039/C9DT00487D  

   Rettig, Irving D.; Van, Jackson; Brauer, Jacob B.; Luo, Wentai; McCormick, Theresa M. (April 2019, Dalton Transactions)

   Tellurorhodamine, 9-mesityl-3,6-bis(dimethylamino)telluroxanthylium hexafluorophosphate ( 1 ), photocatalytically oxidizes aromatic and aliphatic silanes and triphenyl phosphine under mild aerobic conditions. Under irradiation with visible light, 1 can react with self-sensitized 1 O 2 to generate the active telluroxide oxidant ( 2 ). Silanes are oxidized to silanols and triphenyl phosphine is oxidized to triphenyl phoshine oxide either using 2 , or 1 with aerobic irradiation. Kinetic experiments coupled with a computational study elucidate possible mechanisms of oxidation for both silane and phosphine substrates. First-order rates were observed in the oxidation of triphenyl phosphine and methyldiphenyl silane, indicating a substitution like mechanism for substrate binding to the oxidized tellurium( iv ). Additionally, these reactions exhibited a rate-dependence on water. Oxidations were typically run in 50 : 50 water/methanol, however, the absence of water decreased the rates of silane oxidation to a greater degree than triphenyl phosphine oxidation. Parallel results were observed in solvent kinetic isotope experiments using D 2 O in the solvent mixture. The rates of oxidation were slowed to a greater degree in silane oxidation by 2 ( k H / k D = 17.30) than for phosphine ( k H / k D = 6.20). Various silanes and triphenyl phosphine were photocatalytically oxidized with 1 (5%) under irradiation with warm white LEDs using atmospheric oxygen as the terminal oxidant. 

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3. The Pursuit of Perphenylterphenyls

   https://doi.org/10.1002/chem.202200931  

   Du, Yuchen; McSkimming, Alex; Mague, Joel_T; Pascal, Jr., Robert_A (June 2022, Chemistry – A European Journal)

   Abstract Tetradecaphenyl‐p‐terphenyl (2) was synthesized from 2,3,5,6‐tetraphenyl‐1,4‐diiodobenzene (11) by two methods. Ullmann coupling of11with pentaphenyliodobenzene (9) gave compound2in 1.7 % yield, and Sonogashira coupling of11with phenylacetylene, followed by a double Diels‐Alder reaction of the product diyne12with tetracyclone (6), gave2in 1.5 % overall yield. The latter reaction also gave the monoaddition product 4‐(phenylethynyl)‐2,2′,3,3′,4′,5,5′,6,6′‐nonaphenylbiphenyl (13) in 4 % overall yield. The X‐ray structures of compounds2and13show them to possess core aromatic rings distorted into shallow boat conformations. Density functional calculations indicate that these unusual structures are not the lowest energy conformations in the gas phase and may be the result of packing forces in the crystal. In addition, while uncorrected DFT calculations indicate that the strain energy in compound2is approximately 50 kcal/mol, dispersion‐corrected DFT calculations suggest that it is essentially unstrained, due to compensating, favorable, intramolecular interactions of its many phenyl rings. An attempted synthesis of tetradecaphenyl‐o‐terphenyl (4) by reaction of diphenylhexatriyne (14) with three equivalents of tetracyclone at 350 °C gave only the diadduct 2‐(phenylethynyl)‐2′,3,3′,4,4′,5,5′,6,6′‐nonaphenylbiphenyl (15) in 17 % yield. Even higher temperatures failed to produce4and lowered the yield of15, perhaps due to rapid decomposition of the starting materials. Ullmann coupling of 3,4,5,6‐tetraphenyl‐1,2‐diiodobenzene (16) and compound9also failed to give compound4. 

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4. Viral Infection Leads to a Unique Suite of Allelopathic Chemical Signals in Three Diatom Host–Virus Pairs

   https://doi.org/10.3390/md22050228  

   Edwards, Bethanie R; Thamatrakoln, Kimberlee; Fredricks, Helen F; Bidle, Kay D; Van_Mooy, Benjamin_A S (May 2024, Marine Drugs)

   Lauritano, Chiara; Ianora, Adrianna (Ed.)

   Ecophysiological stress and the grazing of diatoms are known to elicit the production of chemical defense compounds called oxylipins, which are toxic to a wide range of marine organisms. Here we show that (1) the viral infection and lysis of diatoms resulted in oxylipin production; (2) the suite of compounds produced depended on the diatom host and the infecting virus; and (3) the virus-mediated oxylipidome was distinct, in both magnitude and diversity, from oxylipins produced due to stress associated with the growth phase. We used high-resolution accurate-mass mass spectrometry to observe changes in the dissolved lipidome of diatom cells infected with viruses over 3 to 4 days, compared to diatom cells in exponential, stationary, and decline phases of growth. Three host virus pairs were used as model systems: Chaetoceros tenuissimus infected with CtenDNAV; C. tenuissimus infected with CtenRNAV; and Chaetoceros socialis infected with CsfrRNAV. Several of the compounds that were significantly overproduced during viral infection are known to decrease the reproductive success of copepods and interfere with microzooplankton grazing. Specifically, oxylipins associated with allelopathy towards zooplankton from the 6-, 9-, 11-, and 15-lipogenase (LOX) pathways were significantly more abundant during viral lysis. 9-hydroperoxy hexadecatetraenoic acid was identified as the strongest biomarker for the infection of Chaetoceros diatoms. C. tenuissimus produced longer, more oxidized oxylipins when lysed by CtenRNAV compared to CtenDNAV. However, CtenDNAV caused a more statistically significant response in the lipidome, producing more oxylipins from known diatom LOX pathways than CtenRNAV. A smaller set of compounds was significantly more abundant in stationary and declining C. tenuissimus and C. socialis controls. Two allelopathic oxylipins in the 15-LOX pathway and essential fatty acids, arachidonic acid (ARA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) were more abundant in the stationary phase than during the lysis of C. socialis. The host–virus pair comparisons underscore the species-level differences in oxylipin production and the value of screening more host–virus systems. We propose that the viral infection of diatoms elicits chemical defense via oxylipins which deters grazing with downstream trophic and biogeochemical effects. 

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5. Ligand-enforced intimacy between a gold cation and a carbenium ion: impact on stability and reactivity

   https://doi.org/10.1039/D0SC05777K  

   Litle, Elishua D.; Wilkins, Lewis C.; Gabbaï, François P. (March 2021, Chemical Science)

   null (Ed.)

   Controlling the reactivity of transition metal complexes by positioning non-innocent functionalities around the catalytic pocket is a concept that has led to significant advances in catalysis. Here we describe our efforts toward the synthesis of dicationic phosphine gold complexes of general formula [( o -Ph 2 P(C 6 H 4 )Carb)Au(tht)] 2+ decorated by a carbenium moiety (Carb) positioned in the immediate vicinity of the gold center. While the most acidic examples of such compounds have limited stability, the dicationic complexes with Carb + = 9- N -methylacridinium and Carb + = [C(Ar N ) 2 ] + (Ar N = p -(C 6 H 4 )NMe 2 ) are active as catalysts for the cycloisomerization of N -propargyl-4-fluorobenzamide, a substrate chosen to benchmark reactivity. The dicationic complex [( o -Ph 2 P(C 6 H 4 )C(Ar N ) 2 )Au(tht)] 2+ , which also promotes hydroarylation and enyne cyclization reactions, displays a higher catalytic activity than its acridinium analog, indicating that the electrophilic reactivity of these complexes scales with the Lewis acidity of the carbenium moiety. These results support the role of the carbenium unit as a non-innocent functionality which can readily enhance the activity of the adjacent metal center. Finally, we also describe our efforts toward the generation and isolation of free γ-cationic phosphines of general formula [( o -Ph 2 P(C 6 H 4 )Carb)] + . While cyclization into phosphonium species is observed for Carb + = [C(Ar N ) 2 ] + , [C(Ph)(Ar N )] + , and 9-xanthylium, [( o -Ph 2 P(C 6 H 4 )-9- N -methylacridinium)] + can be isolated as an air stable, biphilic derivative with uncompromised Lewis acidic and basic properties. 

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