Studies on the Condensation Pathway to and Properties of Diiron Azadithiolate Carbonyls

Reaction of Fe2(SH)2(CO)6 and HCHO, which gives Fe2[(SCH2)2NH](CO)6 in the presence of NH3, affords the possible intermediate Fe2(SCH2OH)2(CO)6, which has been characterized crystallographically as its axial−equatorial isomer. Fe2(SCH2OH)2(CO)6 was shown to react with ammonia and amines to give Fe2[(SCH2)2NR](CO)6 (R = H, alkyl). Related hemithioacetal intermediates were generated by treatment of Fe2(SH)2(CO)6 with RC(O)C(O)R (R = H, Ph, 4-F-C6H4) to give cycloadducts. The benzil derivative Fe2[S2C2(OH)2Ph2](CO)6, a C2-symmetric species, was also characterized crystallographically. The acylated azadithiolate Fe2[(SCH2)2NAc](CO)6 was prepared by reaction of Li2Fe2S2(CO)6 with (ClCH2)2NC(O)Me. DNMR experiments show that the free energies of activation for rotation of the amide bond are the same for Fe2[(SCH2)2NAc](CO)6 and Fe2[(SCH2)2NAc](CO)4(PMe3)2, which implies that the ligands on the iron centers do not strongly affect the basicity of the nitrogen. As a control, we showed that the thioamide Fe2[(SCH2)2NC(S)Me](CO)6 does exhibit a significantly higher barrier to rotation, attributable to the increased double-bond character of the N−C(S) bond.二巯基六羰基二铁（Fe₂(SH)₂(CO)₆）与甲醛（HCHO）在氨（NH₃）存在下反应生成二[(亚甲氨基)二硫]六羰基二铁（Fe₂[(SCH₂)₂NH](CO)₆），该反应可得到可能的中间体二(羟甲基巯基)六羰基二铁（Fe₂(SCH₂OH)₂(CO)₆），该中间体已通过晶体学表征确定其为轴向-赤道异构体。实验表明，二(羟甲基巯基)六羰基二铁可与氨及各类胺反应，生成二[(亚烷基氨基)二硫]六羰基二铁（Fe₂[(SCH₂)₂NR](CO)₆，其中R为氢或烷基）。通过将二巯基六羰基二铁与二羰基化合物RC(O)C(O)R（R为氢、苯基（Ph）、对氟苯基（4-F-C₆H₄））反应，可得到相关的半缩硫醛（hemithioacetal）中间体与环加合物。苯偶酰（benzil）衍生物二[二(羟基二苯基二硫)]六羰基二铁（Fe₂[S₂C₂(OH)₂Ph₂](CO)₆）为C₂对称（C2-symmetric）物种，同样通过晶体学完成表征。酰化氮杂二硫醇盐（azadithiolate）配合物二[(亚甲乙酰氨基)二硫]六羰基二铁（Fe₂[(SCH₂)₂NAc](CO)₆），可通过二锂六羰基二铁二硫盐（Li₂Fe₂S₂(CO)₆）与N,N-二(氯甲基)乙酰胺[(ClCH₂)₂NCOCH₃]反应制备得到。动态核磁共振（DNMR）实验结果显示，二[(亚甲乙酰氨基)二硫]六羰基二铁与二[(亚甲乙酰氨基)二硫]四(三甲基膦（PMe₃）)二铁（Fe₂[(SCH₂)₂NAc](CO)₄(PMe₃)₂）的酰胺键旋转活化自由能一致，这表明铁中心的配体并不会显著影响氮原子的碱性。作为对照实验，我们发现硫代酰胺（thioamide）配合物二[(亚甲硫代乙酰氨基)二硫]六羰基二铁（Fe₂[(SCH₂)₂NC(S)Me](CO)₆）确实表现出显著更高的旋转能垒，这可归因于N−C(S)键的双键特性增强。