Desymmetrized diiron azadithiolato, carbonyls: A step toward modeling the iron-only hydrogenases
Desymmetrized diiron azadithiolato, carbonyls: A step toward modeling the iron-only hydrogenases
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DOI：
10.1021/om7009599
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发表时间：
2008-01-14
期刊：
影响因子：
2.8
通讯作者：
Zampella, Guiseppe
中科院分区：
文献类型：
--
作者：
Stanley, Jane L.;Heiden, Zachariah M.;Zampella, Guiseppe
Fe-2（SH）（2）（CO）（6）、乙醛和（NH 4）（2）CO 3缩合得到甲基取代的氮杂二硫醇盐Fe-2[（SCHMe）（2）NH]（CO）（6）（1）。该配合物主要以内消旋体形式存在（约占95%），但也可检测到d，l非对映异构体。DFT计算预测，内消旋异构体将是2.5千卡/摩尔更稳定的比d，1异构体由于传统的非键的甲基基团和环氢原子之间的相互作用。内消旋-1的晶体学分析证实，两个甲基是赤道的，约束的diferraazadithiolate自行车的构象，desymmetrizes的二铁中心。通过在Fe（CO）（3）基团处快速旋转的条件下在FeCO区域中观察到两个C-13 NMR信号，证实了降低的对称性。1中的胺的p&值为7.89（所有pK（a）在MeCN溶液中测定），其类似于Fe-2[（SCH 2）（2）NH]（CO）（6）（2，pK（a）= 7.98）的重新测定值，并且仅比叔胺Fe-2[（SCH 2）（2）NMe]（CO）（6）（pK（a）= 8.14）碱性稍低。通过Fe-2[（SCHMe）（2）NH]（CO）（5）（PMe 3）的两种异构体的中间作用，1被PMe 3取代，得到Fe-2[（SCHMe）（2）NH]（CO）（4）（PMe 3）（2）（3）。P-31 NMR谱证实3中的两个PMe 3配体是不等价的，与二硫醇盐的去对称化效应一致。发现3中胺的pKa值为11.3。用三苯基膦合成了Fe-2[（SCHMe）（2）NH]（CO）（5）（PPh 3）的单一区域异构体。
Condensation of Fe-2(SH)(2)(CO)(6), acetaldehyde, and (NH4)(2)CO3 affords the methyl-substituted azadithiolate Fe-2[(SCHMe)(2)NH](CO)(6) (1). The complex exists mainly (similar to 95%) as the meso diastercomer, but the d,l diastereoisomers could be detected. DFT calculations predict that the meso isomer would be 2.5 kcal/mol more stable than the d, 1 isomer due to conventional nonbonding interactions between the methyl groups and the ring hydrogen atoms. Crystallographic analysis of meso-1 confirms that the two methyl groups are equatorial, constraining the diferraazadithiolate bicycle to a conformation that desymmetrizes the diiron center. The lowered symmetry is confirmed by the observation of two C-13 NMR signals in the FeCO region under conditions of fast turnstile rotation at the Fe(CO)(3) groups. The p& value of the amine in 1 is 7.89 (all pK(a)'s determined in MeCN solution), which is similar to a redetermined value for Fe-2[(SCH2)(2)NH](CO)(6) (2, pK(a) = 7.98) and only slightly less basic than the tertiary amine Fe-2[(SCH2)(2)NMe](CO)(6) (pK(a) = 8.14). Substitution of 1 with PMe3 proceeded via the intermediacy of two isomers of Fe-2[(SCHMe)(2)NH](CO)(5)(PMe3), affording Fe-2[(SCHMe)(2)NH](CO)(4)(PMe3)(2) (3). P-31 NMR spectra confirm that the two PMe3 ligands in 3 are nonequivalent, consistent with the desymmetrizing effect of the dithiolate. The pKa value of the amine in 3 was found to be 11.3. Using triphenylphosphine, we prepared Fe-2[(SCHMe)(2)NH](CO)(5)(PPh3) as a single regioisomer.