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1. 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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2. Anodically Grown Pt(II) Oxide Microelectrode/Nanoelectrode pH Sensor

   https://doi.org/10.1149/1945-7111/ad8c35  

   Bahdad, Abdullah_Omar O; Leonard, Kevin C (November 2024, Journal of The Electrochemical Society)

   Operandomeasurements of local pH at the nanoscale can significantly improve the understanding of the complex microenvironments that exist in electrochemical systems. However, attempts to easily fabricate a nano-sized pH electrode that can operate under a wide range of pH conditions and have fast temporal responses have been difficult. Here, we show that an anodic-grown Pt/Pt(II) oxide pH sensor manufactured in alkaline conditions (1 M NaOH) shows a near-Nernstian response (−60 mV/pH) from pH 0 to pH 14, is insensitive to dissolved oxygen, cation, and anion identities, and responds correctly in solution with different ionic strengths. This is in contrast to Pt/Pt(II) oxide films grown in acidic media, which do not demonstrate a Nernstian relationship due to cation interference other than H⁺. We observed a response time of 2.25 s, corresponding to 90% of the final measured pH, for an approximately twelve-fold pH step change when growing the Pt(II) oxide layer on a platinum nanoelectrode. Our findings emphasize the influence of solution pH used for anodization synthesis on the anodic Pt(II) oxide pH sensing properties. The direct oxidation approach for fabricating Pt/Pt(II) oxide microelectrode/nanoelectrode pH sensors can simplify the manufacture of real-time pH sensors for complex aqueous environments. 

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3. Effect of synthesis pH and EDTA on iron hexacyanoferrate for sodium-ion batteries

   https://doi.org/10.1039/D0SE00120A  

   Neale, Zachary G.; Liu, Chaofeng; Cao, Guozhong (June 2020, Sustainable Energy & Fuels)

   Iron hexacyanoferrate (FeHCF) particles were synthesized at room temperature with ethylenediaminetetraacetic acid (EDTA) at varying pH. The presence of EDTA produced faceted particles and increasing synthesis pH resulted in slower reaction kinetics and larger particles with lower water content and fewer anion vacancies determined by TGA and Mössbauer spectroscopy. Electrochemical testing of sodium metal half cells revealed higher capacity in FeHCF particles grown at lower pH with EDTA, obtaining a maximum discharge capacity of 151 mA h g −1 with 79% capacity retention after 100 cycles at 100 mA g −1 and a rate capability of 122 mA h g −1 at 3.2 A g −1 . In contrast, particles grown at higher pH had stunted low-spin Fe redox activity but with improved long-term cyclic stability. These findings demonstrate that small changes in synthesis pH can greatly affect the growth and electrochemical properties of FeHCF when using a pH sensitive chelating agent such as EDTA. 

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4. Widespread scope for coral adaptation under combined ocean warming and acidification

   https://doi.org/10.1098/rspb.2024.1161  

   Jury, Christopher P; Toonen, Robert J (September 2024, Proceedings of the Royal Society B: Biological Sciences)

   Reef-building coral populations are at serious risk of collapse due to the combined effects of ocean warming and acidification. Nonetheless, many corals show potential to adapt to the changing ocean conditions. Here we examine the broad sense heritability (H²) of coral calcification rates across an ecologically and phylogenetically diverse sampling of eight of the primary reef-building corals across the Indo-Pacific. We show that all eight species exhibit relatively high heritability of calcification rates under combined warming and acidification (0.23–0.56). Furthermore, tolerance to each factor is positively correlated and the two factors do not interact in most of the species, contrary to the idea of trade-offs between temperature and pH sensitivity, and all eight species can co-evolve tolerance to elevated temperature and reduced pH. Using these values together with historical data, we estimate potential increases in thermal tolerance of 1.0–1.7°C over the next 50 years, depending on species. None of these species are probably capable of keeping up with a high global change scenario and climate change mitigation is essential if reefs are to persist. Such estimates are critical for our understanding of how corals may respond to global change, accurately parametrizing modelled responses, and predicting rapid evolution. 

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5. A cationic gold-fluorenyl complex with a dative Au → C ⁺ bond: synthesis, structure, and carbophilic reactivity

   https://doi.org/10.1039/D2CC05436A  

   Litle, Elishua D.; Gabbaï, François P. (January 2023, Chemical Communications)

   Aiming to study the interaction of gold with the highly Lewis acidic fluorenyl cation, we synthesised ( o -[Ph 2 P(C 6 H 4 )Flu)AuCl(tht)][BF 4 ] ([2][BF 4 ]) and ( o -Ph 2 P(C 6 H 4 )Flu)AuCl 2 (3) (Flu = 9-fluorenyl) and found that the latter could be converted into [( o -Ph 2 P(C 6 H 4 )Flu)AuCl] + ([4] + ) upon treatment with NaBArF 24 (BArF 24 = B(3,5-C 6 H 3 (CF 3 ) 2 ) 4 ). [4] + , which has been isolated as a chloride-bridged dimer, readily catalyses the cycloisomerisation of 2-allyl-2-(2-propynyl)malonate. Computational results show that [4] + possesses a strong Au → C + bond and readily activates enynes. 

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