Formate received significant attention for storing H 2 in chemical bonds using the concept of H 2 carriers. In this report, hydrogen generation from formate was optimized systematically by varying reaction variables. Initial mass activity with a turnover frequency of 3200 mol H 2 mol Pd −1 h −1 and 92% H 2 yield were obtained in sodium formate (7 M 2.0 mL) dehydrogenation over Pd(3 wt %)/C at 80 °C. Influence of formate cations (Na, K, and NH 4 ) on dehydrogenation was also elucidated, presenting that the fastest initial reaction kinetics was achieved with ammonium formate, whereas the highest H 2 yield was obtained with potassium formate (PF) in multiple catalyst recycle tests. Finally, an on-site power generation system was integrated, where a proton exchange membrane fuel cell (PEMFC) was operated in conjunction with H 2 produced from the custom developed semibatch dehydrogenation reactors. The system operation was demonstrated with continuous feeding of PF to generate H 2 and power on demand without an external heat source by utilizing waste heat produced from the PEMFC in a highly efficient manner.
1H-Azadienes were synthesized from allyl azides by ruthenium catalysis under mild and neutral conditions. Applications of the 1H-azadienes were demonstrated for the one-pot synthesis of N-benzyl-1-azadienes, hydrazones, tertiary carbinamines, dieneamide, and N-cyclohexenylacetamides. Two 1H-azatrienes were also synthesized, which were transformed to pyridine derivatives. a,b-Unsaturated imines are highly versatile building blocks for the synthesis of various nitrogen-containing compounds, because they act as N-nucleophiles 1 as well as electrophiles in 1,2-addition and Michael-type 1,4-addition reactions. 2 They also participate as heterodienes in cycloaddition reactions to give heterocyclic compounds. Including the classical condensation reaction between a,b-unsaturated carbonyl compounds and amines, 2a,c,g there are many methods to afford a,b-unsaturated imines having various substituents on the nitrogen. 3 However, those for N-unsubstituted a,b-unsaturated imines (1H-azadienes), which can be regarded as the synthetically most versatile type, are rare and limited in substrate scope. 4-6 In fact, N-unsubstituted imines (N-H imines) are known to have low stability and utilized as in situ generated intermediates (Scheme 1). One of the most common methods to generate 1H-azadienes is the three component reaction of phosphonates, nitriles, and aldehydes. 4 However, the substrate scope is limited to linear a,b-unsaturated N-H ketimines that can survive under conditions using organolithium reagents. Another method is the indium-mediated 1,2-addition reaction toward a,b-unsaturated nitriles. 5 This method also has a limited substrate scope, because only simple allyl-and benzyl bromides are effective to give a,b-unsaturated N-H ketimines. An intermediate 1H-azadiene in the reaction of ammonia and an a,b-unsaturated carbonyl compound has been reported, which was subjected to the in situ reaction with allyl boronates to give a homoallylic amine. However, the use of excessive ammonia was required for the tandem reaction, and only the result of employing nonenolizable verbenone was reported. 6 Recently, a variation of the condensation reaction using Ti(OiPr) 4 and triethylamine as additives has been developed and applied for the synthesis of dienamides. 7 The use of excessive Ti(OiPr) 4 requires a complicated work-up procedure to remove titanium species from the reaction mixture. Herein we wish to report a new and simple method for the synthesis of a wide range of 1H-azadienes from allyl azides under mild and neutral conditions using a diruthenium catalyst 1. The 1H-azadienes were characterized by NMR and IR spectroscopy and utilized in one-pot transformations to give valuable nitrogen-containing compounds.Recently, we found an interesting catalytic activity of the diruthenium complex 1 transforming alkyl azides to N-H imines under the illumination of household uorescent light. 8 Although the N-H imines produced from aliphatic azides are generally unstable due to isomerization and self-condensation reactions, those from ben...
Enamides were synthesized by a ruthenium‐catalyzed one‐pot, one‐step procedure from alkyl azides and acid anhydrides. The substrate scope includes not only secondary azides, but also primary aliphatic ones to give a wide range of enamides containing various functional groups. This one‐step procedure was based on the newly discovered activity of Severin's diruthenium complex ([Cp^RuCl2]2: Cp^=η5‐1‐methoxy‐2,4‐di‐tert‐butyl‐3‐neopentylcyclopentadienyl) for the transformation of alkyl azides into the corresponding N−H imine intermediates in ionic liquids. The formation of ruthenium tetrazene complexes was observed in the stoichiometric reaction of Severin's complex with alkyl azides, which acted as the catalyst for the formation of N−H imine intermediates.
N‐Acylketimines were synthesized through a ruthenium‐catalyzed generation of N–H ketimines from secondary azides and subsequent acylation with mixed anhydrides under mild conditions. The synthetic scope was broad to give N‐acylimines having various functional groups, including those with aliphatic groups that are prone to tautomerization to the corresponding enamides. In addition, various acyl moieties were accommodated. The synthetic utility of this chemoselective imine generation was illustrated by a highly diastereoselective nucleophilic addition of a Grignard reagent to a cyclic N‐acylimine.magnified image
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