- Insight into the Alkaline Stability of N-Heterocyclic Ammonium Groups for Anion-Exchange Polyelectrolytes
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The alkaline stability of N-heterocyclic ammonium (NHA) groups is a critical topic in anion-exchange membranes (AEMs) and AEM fuel cells (AEMFCs). Here, we report a systematic study on the alkaline stability of 24 representative NHA groups at different hydration numbers (λ) at 80 °C. The results elucidate that γ-substituted NHAs containing electron-donating groups display superior alkaline stability, while electron-withdrawing substituents are detrimental to durable NHAs. Density-functional-theory calculations and experimental results suggest that nucleophilic substitution is the dominant degradation pathway in NHAs, while Hofmann elimination is the primary degradation pathway for NHA-based AEMs. Different degradation pathways determine the alkaline stability of NHAs or NHA-based AEMs. AEMFC durability (from 1 A cm?2 to 3 A cm?2) suggests that NHA-based AEMs are mainly subjected to Hofmann elimination under 1 A cm?2 current density for 1000 h, providing insights into the relationship between current density, λ value, and durability of NHA-based AEMs.
- Chen, Nanjun,Fan, Jiantao,Hu, Chuan,Jin, Yiqi,Lee, Young Moo,Li, Hui,Liu, Haijun,Wu, Bo,Xu, Shaoyi
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supporting information
p. 19272 - 19280
(2021/07/25)
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- A general and practical sulfonylation of benzylic ammonium salts with sulfonyl hydrazides for the synthesis of sulfones
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A practical and efficient approach adopting transition-metal-free cross-coupling of sulfonyl hydrazides with benzyl ammonium salts has been developed to synthesize benzyl sulfones using Cs2CO3 as base under mild conditions. The protocol employs stable and easy to handle coupling partners, and is endowed with good substrate compatibility, leading to functional benzyl sulfones in good yields.
- Zhu, Haibo,Zhang, Yingying,Liu, Yishuai,Yang, Liu,Xie, Zongbo,Jiang, Guofang,Le, Zhang-Gao
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supporting information
(2020/05/06)
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- Ni-Catalyzed Iterative Alkyl Transfer from Nitrogen Enabled by the in Situ Methylation of Tertiary Amines
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Current methods to achieve transition-metal-catalyzed alkyl carbon-nitrogen (C-N) bond cleavage require the preformation of ammonium, pyridinium, or sulfonamide derivatives from the corresponding alkyl amines. These activated substrates permit C-N bond cleavage, and their resultant intermediates can be intercepted to affect carbon-carbon bond-forming transforms. Here, we report the combination of in situ amine methylation and Ni-catalyzed benzalkyl C-N bond cleavage under reductive conditions. This method permits iterative alkyl group transfer from tertiary amines and demonstrates a deaminative strategy for the construction of Csp3-Csp3 bonds. We demonstrate PO(OMe)3 (trimethylphosphate) to be a Ni-compatible methylation reagent for the in situ conversion of trialkyl amines into tetraalkylammonium salts. Single, double, and triple benzalkyl group transfers can all be achieved from the appropriately substituted tertiary amines. Transformations developed herein proceed via recurring events: The in situ methylation of tertiary amines by PO(OMe)3, Ni-catalyzed C-N bond cleavage, and concurrent Csp3-Csp3 bond formation.
- Nwachukwu, Chideraa Iheanyi,McFadden, Timothy Patrick,Roberts, Andrew George
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p. 9979 - 9992
(2020/09/03)
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- Addition of amines to a carbonyl ligand: Syntheses, characterization, and reactivities of iridium(iii) porphyrin carbamoyl complexes
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Treatment of (carbonyl)chloro(meso-tetra-p-tolylporphyrinato)iridium(III), (TTP)Ir(CO)Cl (1), with excess primary amines at 23°C in the presence of Na2CO3 produces the trans-amine-coordinated iridium carbamoyl complexes (TTP)Ir(NH2R)[C(O)NHR] (R = Bn (2a), n-Bu (2b), i-Pr (2c), t-Bu (2d)) with isolated yields up to 94%. The trans-amine ligand is labile and can be replaced with quinuclidine (1-azabicyclo[2.2.2]octane, ABCO), 1-methylimidazole (1-MeIm), triethyl phosphite (P(OEt)3), and dimethylphenylphosphine (PMe2Ph) at 23°C to afford the hexacoordinated carbamoyl complexes (TTP)Ir(L)[C(O)NHR] (for R = Bn: L = ABCO (3a), 1-MeIm (4a), P(OEt)3 (5a), PMe2Ph (6a)). On the basis of ligand displacement reactions and equilibrium studies, ligand binding strengths to the iridium metal center were found to decrease in the order PMe2Ph > P(OEt)3 > 1-MeIm > ABCO > BnNH 2 ? Et3N, PCy3. The carbamoyl complexes (TTP)Ir(L)[C(O)NHR] (L = RNH2 (2a,b), 1-MeIm (4a)) undergo protonolysis with HBF4 to give the cationic carbonyl complexes [(TTP)Ir(NH2R)(CO)]BF4 (7a,b) and [(TTP)Ir(1-MeIm)(CO)] BF4 (8), respectively. In contrast, the carbamoyl complexes (TTP)Ir(L)[C(O)NHR] (L = P(OEt)3 (5a), PMe2Ph (6a,c)) reacted with HBF4 to afford the complexes [(TTP)Ir(PMe 2Ph)]BF4 (9) and [(TTP)IrP(OEt)3]BF4 (10), respectively. The carbamoyl complexes (TTP)Ir(L)[C(O)NHR] (L = RNH 2 (2a-d), 1-MeIm (4a), P(OEt)3 (5b), PMe2Ph (6c)) reacted with methyl iodide to give the iodo complexes (TTP)Ir(L)I (L = RNH2 (11a-d), 1-MeIm (12), P(OEt)3 (13), PMe2Ph (14)). Reactions of the complexes [(TTP)Ir(PMe2Ph)]BF4 (9) and [(TTP)IrP(OEt)3]BF4 (10) with [Bu4N]I, benzylamine (BnNH2), and PMe2Ph afforded (TTP)Ir(PMe 2Ph)I (14), (TTP)Ir[P(OEt)3]I (13), [(TTP)Ir(PMe 2Ph)(NH2Bn)]BF4 (16), and trans-[(TTP) Ir(PMe2Ph)2]BF4 (17), respectively. Metrical details for the molecular structures of 4a and 17 are reported.
- Dairo, Taiwo O.,Ellern, Arkady,Angelici, Robert J.,Woo, L. Keith
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p. 2266 - 2276
(2014/06/09)
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- Mechanism of the Stevens rearrangement of ammonium ylides
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Isomerization of trimethylammonium N-benzylide 2 failed to occur at room temperature in a non-basic medium (HMPA) or at -78°C in the presence of butyllithium in THF. However, N,N-dimethyl-1-phenylethylamine 4 (Stevens rearrangement product) was formed when the temperature of the latter reaction was raised to room temperature. The mechanism of the Stevens rearrangement is discussed.
- Maeda, Yasuhiro,Sato, Yoshiro
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p. 1491 - 1493
(2007/10/03)
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- A Microscopic Hydrophobicity Parameter
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p-Nitrophenyl laurate at 1x1E-5 M in water forms aggregates within which the ester groups hydrolyze slowly (about 1E3 less than a short-chain monomer).Salts of the general structure RNMe3+X- disrupt or destroy the aggregates; the ester groups are thereby "deshielded", and the observed hydrolysis rate increases.The magnitude of the rate increase at a given salt concentration depends on R: the more hydrophobic the R group, the greater the rate enhancement.This observation provided the basis of a "microscopic" hydrophobicity parameter MH which was evaluated for 25 different Rs (e.g., MH=0.73, 0.97, and 1.33 for R=ethyl, n-butyl, and n-hexyl).MH values were used to assess the role of branching, unsaturation, cyclization, aromaticity, halogenation, etc., in hydrophobic association.The parameters correlate well with Hansch ? values for aliphatic substituents but not for aromatic groups.Since the MH scale is based on the specific binding of one molecule to another, it may be well suited for modeling association among bioactive species.
- Menger, F. M.,Venkataram, U. V.
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p. 2980 - 2984
(2007/10/02)
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