Chemistry of the Si−Si and Fe−Fe Bonds in the Cyclic Structure (Me2SiSiMe2)[η5-C5H4Fe(CO)2]2. Selective Cleavage of the Fe−Fe Bond by I2 and Unexpected Properties of the Iodide

The Si−Si bond in the title cyclic structure (1) exhibited unexpected stability toward I2. Thus, the reaction of 1 with
1 equiv of I2 in chloroform resulted in selective cleavage of the Fe−Fe bond to afford diiodide (Me2SiSiMe2)[η5-C5H4Fe(CO)2I]2 (2) with retention of the Si−Si bond. When excess (2−4 equiv) I2 was used to react with 1 in either
benzene or chloroform, iodonium-bridged diiron complex {(Me2SiSiMe2)[η5-C5H4Fe(CO)2]2I+}(I5-) (4) was obtained,
in which the Si−Si bond was still retained. It is noteworthy that 4 contains a counteranion I5- rather than the
expected I3-, which is the first example for an iodonium-bridged diiron complex to combine a polyiodide anion
larger than I3-. UV irradiation of 2 did not affect the stability of the silicon−silicon bond and, in the presence of
PR3, resulted in CO substitution to give (Me2SiSiMe2)[η5-C5H4Fe(CO)(PR3)I]2 (5, R = Ph; 6, R = OPh). The
molecular structure of 2 was determined by the X-ray diffraction method. It is noteworthy that the structure of 2
does not take the expected anti conformation but adopts a gauche one. The length of the Si−Si bond of 2 [2.353(3) Å] is about the same as that of 1 [2.346(4) Å], which can be direct evidence to demonstrate that the Si−Si bond
in the cyclic structure of 1 is not subject to significant ring strain. The molecular structure of 4 was also determined
by the X-ray diffraction method. It is noted that the structure of 4 contains an abnormally large Fe−I+−Fe bond
angle of 121.25(7)°. Of particular interest is the observation that the I5- anions of 4 are self-assembled into novel
layered, two-dimensional networks with the (Me2SiSiMe2)[η5-C5H4Fe(CO)2]2I+ cations as the template.

标题所述的环状结构（1）中的Si-Si键对I2表现出出人意料的稳定性。因此，1与氯仿中的1当量I2的反应导致Fe-Fe键的特异性断裂，从而得到保留Si-Si键的二碘化物（Me2SiSiMe2)[η5-C5H4Fe(CO)2I]2（2）。当使用过量（2-4当量）的I2与1在苯或氯仿中反应时，得到了含有碘桥接的二铁配合物{(Me2SiSiMe2)[η5-C5H4Fe(CO)2]2I+}(I5-)（4），其中Si-Si键仍然得到保留。值得注意的是，4含有反常的共轭阴离子I5-而非预期的I3-，这为碘桥接的二铁配合物结合大于I3-的多碘化物阴离子的首次实例。UV辐射对2的硅-硅键稳定性无影响，并在PR3的存在下导致CO被PR3取代，生成（Me2SiSiMe2)[η5-C5H4Fe(CO)(PR3)I]2（5，R = Ph；6，R = OPh）。2的分子结构通过X射线衍射法确定。值得注意的是，2的结构未采取预期的反式构象，而是采取了顺式构象。2中的Si-Si键长度[2.353(3) Å]与1中的[2.346(4) Å]大致相同，这可以直接证明1的环状结构中的Si-Si键未受到显著的环应变。4的分子结构也通过X射线衍射法确定。值得注意的是，4的结构包含一个异常大的Fe-I+−Fe键角121.25(7)°。特别值得注意的是，4中的I5-阴离子以（Me2SiSiMe2)[η5-C5H4Fe(CO)2]2I+阳离子为模板，自组装成新颖的层状二维网络。