N-Substituted Derivatives of the Azadithiolate Cofactor from the [FeFe] Hydrogenases: Stability and Complexation

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• 作者：Raja Angamuthu ; Chi-Shian Chen ; Tyler R. Cochrane ; Danielle L. Gray ; David Schilter ; Olbelina A. Ulloa ; Thomas B. Rauchfuss
• 刊名：Inorganic Chemistry
• 出版年：2015
• 出版时间：June 15, 2015
• 年：2015
• 卷：54
• 期：12
• 页码：5717-5724
• 全文大小：429K
• ISSN：1520-510X

文摘

Experiments are described that probe the stability of N-substituted derivatives of the azadithiolate cofactor recently confirmed in the [FeFe] hydrogenases (Berggren, G., et al. Nature 2013, 499, 66). Acid-catalyzed hydrolysis of bis(thioester) BnN(CH₂SAc)₂ gives [BnNCH₂SCH₂]₂ rather than azadithiol BnN(CH₂SH)₂. Treatment of BnN(CH₂SAc)₂ with NaO^tBu generates BnN(CH₂SNa)₂, which was trapped with NiCl₂(diphos) (diphos = 1,2-C₂H₄(PR₂)₂; R = Ph (dppe) and Cy (dcpe)) to give fully characterized complexes Ni[(SCH₂)₂NBn](diphos). The related N-aryl derivative Ni[(SCH₂)₂NC₆H₄Cl](diphos) was prepared analogously from 4-ClC₆H₄N(CH₂SAc)₂, NaO^tBu, and NiCl₂(dppe). Crystallographic analysis confirmed that these rare nonbridging [adt^R]^{2鈥?/sup> complexes feature distorted square planar Ni centers. The analogue Pd[(SCH₂)₂NBn](dppe) was also prepared. 31P NMR analysis indicates that Ni[(SCH₂)₂NBn](dppe) has basicity comparable to typical amines. As shown by cyclic voltammetry, the couple [M[(SCH₂)₂NBn](dppe)]+/0 is reversible near 鈭?.0 V versus Fc+/0. The wave shifts to 鈭?.78 V upon N-protonation. In the presence of CF₃CO₂H, Ni[(SCH₂)₂NBn](dppe) catalyzes hydrogen evolution at rate of 22 s鈥? in the acid-independent regime, at room temperature in CH₂Cl₂ solution. In contrast to the instability of RN(CH₂SH)₂ (R = alkyl, aryl), the dithiol of tosylamide TsN(CH₂SH)₂ proved sufficiently stable to allow full characterization. This dithiol reacts with Fe₃(CO)₁₂ and, in the presence of base, NiCl₂(dppe) to give Fe₂[(SCH₂)₂NTs](CO)₆ and Ni[(SCH₂)₂NTs](dppe), respectively.}