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 <b>2013b>, 499, 66). Acid-catalyzed hydrolysis of bis(thioester) BnN(CHb>2b>SAc)b>2b> gives [BnNCHb>2b>SCHb>2b>]b>2b> rather than azadithiol BnN(CHb>2b>SH)b>2b>. Treatment of BnN(CHb>2b>SAc)b>2b> with NaO^tBu generates BnN(CHb>2b>SNa)b>2b>, which was trapped with NiClb>2b>(diphos) (diphos = 1,2-Cb>2b>Hb>4b>(PRb>2b>)b>2b>; R = Ph (dppe) and Cy (dcpe)) to give fully characterized complexes Ni[(SCHb>2b>)b>2b>NBn](diphos). The related N-aryl derivative Ni[(SCHb>2b>)b>2b>NCb>6b>Hb>4b>Cl](diphos) was prepared analogously from 4-ClCb>6b>Hb>4b>N(CHb>2b>SAc)b>2b>, NaO^tBu, and NiClb>2b>(dppe). Crystallographic analysis confirmed that these rare nonbridging [adt^R]^{2鈥?/sup> complexes feature distorted square planar Ni centers. The analogue Pd[(SCHb>2b>)b>2b>NBn](dppe) was also prepared. 31P NMR analysis indicates that Ni[(SCHb>2b>)b>2b>NBn](dppe) has basicity comparable to typical amines. As shown by cyclic voltammetry, the couple [M[(SCHb>2b>)b>2b>NBn](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 CFb>3b>COb>2b>H, Ni[(SCHb>2b>)b>2b>NBn](dppe) catalyzes hydrogen evolution at rate of 22 s鈥? in the acid-independent regime, at room temperature in CHb>2b>Clb>2b> solution. In contrast to the instability of RN(CHb>2b>SH)b>2b> (R = alkyl, aryl), the dithiol of tosylamide TsN(CHb>2b>SH)b>2b> proved sufficiently stable to allow full characterization. This dithiol reacts with Feb>3b>(CO)b>12b> and, in the presence of base, NiClb>2b>(dppe) to give Feb>2b>[(SCHb>2b>)b>2b>NTs](CO)b>6b> and Ni[(SCHb>2b>)b>2b>NTs](dppe), respectively.}