Synthetic and Structural Studies on l-Cysteinyl Group-Containing Diiron/Triiron Azadithiolates as Active Site Models of [FeFe]-Hydrogenases

Five new l-cysteinyl group-containing diiron/triiron azadithiolate complexes (3−6, 10), which could be regarded as the active site models of [FeFe]-hydrogenases, have been successfully synthesized. Treatment of l-cysteinyl sodium mercaptide CytSNa (1, Cyt = CH2CH(CO2Et)NH(CO2Bu-t) with complex [(μ-SCH2)2NCH2CH2Br]Fe2(CO)6 (2) in THF at room temperature resulted in formation of model complex [(μ-SCH2)2NCH2CH2SCyt]Fe2(CO)6 (3). Further treatment of 3 with decarbonylating agent Me3NO in MeCN at room temperature afforded model complex [(μ-SCH2)2NCH2CH2SCyt]Fe2(CO)5 (4). Similarly, treatment of 3 with an equimolar mixture of Me3NO and Ph3P gave model complex [(μ-SCH2)2NCH2CH2SCyt]Fe2(CO)5(Ph3P) (5) and further treatment of 5 with Me3NO produced model complex [(μ-SCH2)2NCH2CH2SCyt]Fe2(CO)4(Ph3P) (6). More interestingly, model complex [(μ-SCH2)2NCH(CO2Et)CH2SFe(CO)2Cp]Fe2(CO)5 (10) could be synthesized by a “one pot” reaction of the in situ prepared (μ-HS)2Fe2(CO)6 (9) with 37% aqueous formaldehyde followed by treatment with the N-deprotected l-cysteinyl iron mercaptide Cp(CO)2FeSCH2CH(CO2Et)NH2 (8). Complex 8 is new, which was prepared by treatment of complex Cp(CO)2FeSCyt (7) with CF3CO2H followed by 25% aqueous NH3. All the new complexes 3−6, 8, and 10 were characterized by elemental analysis and various spectroscopic techniques, whereas complexes 5 and 10 were further characterized by X-ray crystallography.

本研究成功合成了5种新型含L-半胱氨酰基的二铁/三铁氮杂二硫醇盐配合物（3~6、10），该类配合物可作为[FeFe]-氢化酶的活性位点模型。将L-半胱氨酰巯基钠CytSNa（1，其中Cyt=CH2CH(CO2Et)NH(CO2Bu-t)）与配合物[(μ-SCH2)2NCH2CH2Br]Fe2(CO)6（2）在四氢呋喃（THF）中室温下反应，得到模型配合物[(μ-SCH2)2NCH2CH2SCyt]Fe2(CO)6（3）。进一步将3与脱羰试剂三甲基氮氧化物（Me3NO）在乙腈（MeCN）中室温下反应，得到模型配合物[(μ-SCH2)2NCH2CH2SCyt]Fe2(CO)5（4）。类似地，将3与等摩尔的Me3NO和三苯基膦（Ph3P）混合反应，得到模型配合物[(μ-SCH2)2NCH2CH2SCyt]Fe2(CO)5(Ph3P)（5）；再将5与Me3NO反应，生成模型配合物[(μ-SCH2)2NCH2CH2SCyt]Fe2(CO)4(Ph3P)（6）。更值得关注的是，通过原位制备的(μ-HS)2Fe2(CO)6（9）与37%甲醛水溶液反应后，再经N-脱保护的L-半胱氨酰铁巯基配合物环戊二烯基（Cp）二羰基铁配合物Cp(CO)2FeSCH2CH(CO2Et)NH2（8）处理，可通过“一锅法”合成模型配合物[(μ-SCH2)2NCH(CO2Et)CH2SFe(CO)2Cp]Fe2(CO)5（10）。配合物8为新型化合物，其制备方法为：将配合物Cp(CO)2FeSCyt（7）用三氟乙酸（CF3CO2H）处理后，再经25%氨水处理得到。所有新型配合物3~6、8及10均通过元素分析及多种光谱技术进行了表征，其中配合物5和10还通过X射线晶体衍射进行了进一步的结构表征。