ChemInform Abstract: Reduction of Substituted 1H‐4,5‐Dihydroimidazolium Salts.

Salerno, Alejandra; Ceriani, Vanina; Perillo, Isabel A.

doi:10.1002/chin.199321156

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(1 citation statement)

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“…It has been previously shown that 1,3-disubstituted imidazolinium cations are reduced to the corresponding imidazolidines by relatively strong reducing agents such as Zn/HCl, 21 NaBH 4 , 22 or LiAlH 4 . 22,23 The results in this study revealed that such conversion can be performed under very mild conditions by the catalytic reaction using H 2 as a reducing agent. 24 To gain an insight into the mechanisms of the catalysis, the effects of proton acceptors and solvents were further investigated for the representative catalysts 4 and 6.…”

Section: ■ Introductionmentioning

confidence: 99%

Reversible Hydride Transfer to N,N′-Diarylimidazolinium Cations from Hydrogen Catalyzed by Transition Metal Complexes Mimicking the Reaction of [Fe]-Hydrogenase

2017

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[Fe]-hydrogenase is a key enzyme involved in methanogenesis and facilitates reversible hydride transfer from H to N,N-methenyltetrahydromethanopterin (CH-HMPT). In this study, a reaction system was developed to model the enzymatic function of [Fe]-hydrogenase by using N,N'-diphenylimidazolinium cation (1) as a structurally related alternative to CH-HMPT. In connection with the enzymatic mechanism via heterolytic cleavage of H at the single metal active site, several transition metal complex catalysts capable of such activation were utilized in the model system. Reduction of 1[BF] to N,N'-diphenylimidazolidine (2) was achieved under 1 atm H at ambient temperature in the presence of an equimolar amount of NEt as a proton acceptor. The proposed catalytic pathways involved the generation of active hydride complexes and subsequent intermolecular hydride transfer to 1. The reverse reaction was accomplished by treatment of 2 with HNMePh as the proton source, where [(η-CMe)Ir{(p-MeCHSO)NCHPhCHPhNH}] was found to catalyze the formation of 1 and H with high efficiency. These results are consistent with the fact that use of 2,6-lutidine in the forward reaction or 2,6-lutidinium in the reverse reaction resulted in incomplete conversion. By combining these reactions using the above Ir amido catalyst, the reversible hydride transfer interconverting 1/H and 2/H was performed successfully. This system demonstrated the hydride-accepting and hydride-donating modes of biologically relevant N-heterocycles coupled with proton concentration. The influence of substituents on the forward and reverse reactivities was examined for the derivatives of 1 and 2 bearing one para-substituted N-phenyl group.

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Section: ■ Introductionmentioning

confidence: 99%