Synthetic and structural studies of mixed sodium bis(trimethylsilyl)amide/sodium halide aggregates in the presence of η2-N,N-, η3-N,N,N/N,O,N-, and η4-N,N,N,N-donor ligands

When the important utility amide sodium bis(trimethylsilyl)amide is combined with hydrocarbon-soluble molecular forms of sodium halide salts, a complex structural chemistry is observed. Through utilization of several different multidentate donor molecules, it is possible to isolate a series of compounds that have structural motifs previously not observed in sodium chemistry

Monodentate coordination of the normally chelating chiral diamine (R,R)-TMCDA

After isolating an unusual binuclear, but monosolvated NaHMDS complex [{(R,R)-TMCDA}·(NaHMDS)2]∞ which polymerises via intermolecular electrostatic Na···MeHMDS interactions, further (R,R)-TMCDA was added to produce the discrete binuclear amide [κ2-{(R,R)-TMCDA}·(NaHMDS)2{κ1-(R,R)-TMCDA}], whose salient feature is the unique monodentate coordination of one of the chiral diamine ligands

Structural studies of cesium, lithium/cesium and sodium/cesium bis(trimethylsilyl)amide (HMDS) complexes

Reacting cesium fluoride with an equimolar n-hexane solution of lithium bis(trimethylsilyl)amide (LiHMDS), allows the isolation of CsHMDS (1) in 80% yield (after sublimation). This preparative route to 1 negates the need for pyrophoric Cs metal or organocesium reagents in its synthesis. If a 2:1 LiHMDS:CsF ratio is employed the heterobimetallic polymer [LiCs(HMDS)2]∞ 2 was isolated (57% yield). By combining equimolar quantities of NaHMDS and CsHMDS in hexane/toluene [NaCs(HMDS)2(toluene)]∞ 3 was isolated (62% yield). Attempts to prepare the corresponding potassium-cesium amide failed, and instead yielded the known monometallic polymer [Cs(HMDS)(toluene)]∞ 4. With the aim of expanding the structural diversity of Cs(HMDS) species, 1 was reacted with several different Lewis basic donor molecules of varying denticity; namely, (R,R)-N,N,N′,N′-tetramethylcyclohexane-1,2-diamine [(R,R)-TMCDA] and N,N,Nʹ,Nʹ-tetramethylethylenediamine (TMEDA), N,N,Nʹ,Nʹʹ,Nʹʹ-pentamethyldiethylenetriamine (PMDETA), tris[2-(dimethylamino)ethyl]amine (Me6-TREN) and tris[2-(2-methoxyethoxy)ethyl]amine (TMEEA). These reactions yielded dimeric [Cs(HMDS)·donor]2 5-7 [where donor is (R,R)-TMCDA, TMEDA and PMDETA respectively], the tetranuclear ‘open’-dimer [{Me6-TREN·Cs(HMDS)}2{Cs(HMDS)}2] 8 and the monomeric Cs(HMDS)·TMEEA 9. Complexes 2,3 and 5-9 were characterized by X-ray crystallography and in solution by multinuclear NMR spectroscopy

Selective Oxidation of Glycerol via Acceptorless Dehydrogenation Driven by Ir(I)-NHC Catalysts

After pandemic, healthcare workers experienced a series of emotional and psychological disturbances that could impact their mental well-being. In this study, the feasibility of morphological characteristics of photoplethysmographic (PPG) waveform to quantify stress and depression level posed by COVID-19 in first-line healthcare workers is explored. Results show that higher stress and depression level are moderately correlated with large systolic amplitude and parameters that might indicate early wave reflection. These results suggest that an arterial stiffness, quantified with PPG morphological characteristics, could provide valuable information in assessing mental healt

Exploring the solid state and solution structural chemistry of the utility amide potassium hexamethyldisilazide (KHMDS)

The structural chemistry of eleven donor complexes of the important Brønsted base potassium 1,1,1,3,3,3-hexamethyldisilazide (KHMDS) has been studied. Depending on the donor, each complex adopted one of four general structural motifs. Specifically, in this study the donors employed were toluene (to give polymeric 1 and dimeric 2), THF (dimeric 3), N,N,N',N'-tetramethylethylenediamine (TMEDA) (dimeric 4), (R,R)-N,N,N',N'-tetramethyl-1,2-diaminocyclohexane [(R,R)-TMCDA] (dimeric 5), 12-crown-4 (dimeric 6), N,N,N',N'-tetramethyldiaminoethyl ether (TMDAE) (tetranuclear dimeric 8 and monomeric 10), N,N,N',N',N''-pentamethyldiethylentriamine (PMDETA) (tetranuclear dimeric 7), tris[2-dimethyl(amino)ethyl]amine (Me6TREN) (tetranuclear dimeric 9) and tris{2-(2-methoxyethoxy)ethyl}amine (TMEEA) (monomeric 11). The complexes were also studied in solution by 1H and 13C NMR spectroscopy as well as DOSY NMR spectroscopy

Catalytic applications of zwitterionic transition metal compounds

This frontiers article highlights recent developments on the application of transition metal-based zwitterionic complexes in catalysis. Recent applications of selected zwitterionic catalysts in polymerization reactions, including the carbonylative polymerization of cyclic ethers, carbon–carbon coupling reactions, the asymmetric hydrogenation of unfunctionalized olefins, and the hydrofunctionalization of alkenes are reviewed. In addition, advances in the field of hydrogenation/dehydrogenation reactions related to energy applications, including the hydrogenation of CO2 and the dehydrogenation of formic acid and N-heterocycles, the functionalization of CO2 with amines and hydrosilanes, and the valorization of polyfunctional bio-based feedstocks, such as the dehygrogenation of glycerol to lactic acid or the reduction of levulinic acid into γ-valerolactone, are also described.Financial support from the Spanish Ministerio de Ciencia e Innovación (MICINN/FEDER) under the Project PID2019-103965GB-I00/AEI/10.13039/501100011033, and the “Departamento de Ciencia, Universidad y Sociedad del Conocimiento del Gobierno de Aragón” (group E42_20R) is gratefully acknowledged.Peer reviewe

Selective Oxidation of Glycerol via Acceptorless Dehydrogenation Driven by Ir(I)-NHC Catalysts

Iridium(I) compounds featuring bridge-functionalized bis-NHC ligands (NHC = N-heterocyclic carbene), [Ir(cod)(bis-NHC)] and [Ir(CO)2(bis-NHC)], have been prepared from the appropriate carboxylate- or hydroxy-functionalized bis-imidazolium salts. The related complexes [Ir(cod)(NHC)2]+ and [IrCl(cod)(NHC)(cod)] have been synthesized from a 3-hydroxypropyl functionalized imidazolium salt. These complexes have been shown to be robust catalysts in the oxidative dehydrogenation of glycerol to lactate (LA) with dihydrogen release. High activity and selectivity to LA were achieved in an open system under low catalyst loadings using KOH as a base. The hydroxy-functionalized bis-NHC catalysts are much more active than both the carboxylate-functionalized ones and the unbridged bis-NHC iridium(I) catalyst with hydroxyalkyl-functionalized NHC ligands. In general, carbonyl complexes are more active than the related 1,5-cyclooctadiene ones. The catalyst [Ir(CO)2{(MeImCH2)2CHOH}]Br exhibits the highest productivity affording TONs to LA up to 15,000 at very low catalyst loadings

Mechanistic Insights on the Functionalization of CO 2

The zwitterionic complex [Cp*IrCl{(MeIm)CHCOO}] (1) efficiently catalyzes the selective hydrosilylation of CO to afford the corresponding silylformate. The best reaction performance has been achieved in acetonitrile at 348 K using HSiMePh. The 1-catalyzed reaction of pyrrolidine with CO and HSiMePh strongly depends on the CO pressure. At low concentration of CO (1 bar) formation of the corresponding silylcarbamate, by insertion of CO into the Si−N bond of the in situ generated silylamine was observed, while at higher pressure (3 bar) the formamide derivative was obtained as major reaction product. The unexpected formation of pyrrolidin-1-ium formate as intermediate of the reaction the 1-catalyzed of CO with pyrrolidine and HSiMePh has been observed, and its role in the formation of 1-formylpyrrolidine rationalized. Moreover, a mechanism for the reaction of CO with hydrosilanes, in the presence and in the absence of amines, based on theoretical calculations has been proposed.The authors express their appreciation for the financial support from MICINN/FEDER projects PGC2018‐099383‐B‐100 and CTQ2016‐75884‐P, and the Regional Government of Aragón/FEDER 2014‐2020 “Building Europe from Aragón” (group E42_17R). J.M. acknowledges the financial support provided by the Spanish “Ministerio de Ciencia, Innovación y Universidades” (FPU14/06003). In addition, the resources from the supercomputer “Memento”, technical expertise and assistance provided by BIFIZCAM (Universidad de Zaragoza) are acknowledged.Peer reviewe

Mechanistic insights on the functionalization of CO2 with amines and hydrosilanes catalyzed by a zwitterionic iridium carboxylate-functionalized bis-NHC catalyst

The zwitterionic complex [Cp*IrCl{(MeIm)CHCOO}] (1) efficiently catalyzes the selective hydrosilylation of CO to afford the corresponding silylformate. The best reaction performance has been achieved in acetonitrile at 348 K using HSiMePh. The 1-catalyzed reaction of pyrrolidine with CO and HSiMePh strongly depends on the CO pressure. At low concentration of CO (1 bar) formation of the corresponding silylcarbamate, by insertion of CO into the Si−N bond of the in situ generated silylamine was observed, while at higher pressure (3 bar) the formamide derivative was obtained as major reaction product. The unexpected formation of pyrrolidin-1-ium formate as intermediate of the reaction the 1-catalyzed of CO with pyrrolidine and HSiMePh has been observed, and its role in the formation of 1-formylpyrrolidine rationalized. Moreover, a mechanism for the reaction of CO with hydrosilanes, in the presence and in the absence of amines, based on theoretical calculations has been proposed.The authors express their appreciation for the financial support from MICINN/FEDER projects PGC2018‐099383‐B‐100 and CTQ2016‐75884‐P, and the Regional Government of Aragón/FEDER 2014‐2020 “Building Europe from Aragón” (group E42_17R). J.M. acknowledges the financial support provided by the Spanish “Ministerio de Ciencia, Innovación y Universidades” (FPU14/06003). In addition, the resources from the supercomputer “Memento”, technical expertise and assistance provided by BIFIZCAM (Universidad de Zaragoza) are acknowledged.Peer reviewe