Hydride Transfer from Iron(II) Hydride Compounds to NAD(P)+ Analogues

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• 作者：Fanjun Zhang ; Jiong Jia ; Shuli Dong ; Wenguang Wang ; Chen-Ho Tung
• 刊名：Organometallics
• 出版年：2016
• 出版时间：April 25, 2016
• 年：2016
• 卷：35
• 期：8
• 页码：1151-1159
• 全文大小：551K
• 年卷期：0
• ISSN：1520-6041

文摘

Iron(II) hydride complexes of the “piano-stool” type, Cp*(P-P)FeH (P-P = dppe (1H), dppbz (2H), dppm (3H), dcpe (4H)) were examined as hydride donors in the reduction of N-benzylpyridinium and acridinium salts. Two pathways of hydride transfer, “single-step H^–” transfer to pyridinium and a “two-step (e^–/H^•)” transfer for acridinium reduction, were observed. When 1-benzylnicotinamide cation (BNA⁺) was used as an H^– acceptor, kinetic studies suggested that BNA⁺ was reduced at the C6 position, affording 1,6-BNAH, which can be converted to the more thermally stable 1,4-product. The rate constant k of H^– transfer was very sensitive to the bite angle of P–Fe–P in Cp*(P-P)FeH and ranged from 3.23 × 10^–3 M^–1 s^–1 for dppe to 1.74 × 10^–1 M^–1 s^–1 for dppm. The results obtained from reduction of a range of N-benzylpyridinium derivatives suggest that H^– transfer is more likely to be charge controlled. In the reduction of 10-methylacridinium ion (Acr⁺), the reaction was initiated by an e^– transfer (ET) process and then followed by rapid disproportionation reactions to produce Acr₂ dimer and release of H₂. To achieve H^• transfer after ET from [Cp*(P-P)FeH]⁺ to acridine radicals, the bulkier acridinium salt 9-phenyl-10-methylacridinium (PhAcr⁺) was selected as an acceptor. More evidence for this “two-step (e^–/H^•)” process was derived from the characterization of PhAcr^• and [4H]⁺ radicals by EPR spectra and by the crystallographic structure confirmation of [4H]⁺. Our mechanistic understanding of fundamental H^– transfer from iron(II) hydrides to NAD⁺ analogues provides insight into establishing attractive bio-organometallic transformation cycles driven by iron catalysis.