Chemistry of the Si-Si and Fe-Fe bonds in the cyclic structure (Me2SiSiMe2)[eta5-C5H4FeCO2]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 I(2). Thus, the reaction of 1 with 1 equiv of I(2) in chloroform resulted in selective cleavage of the Fe-Fe bond to afford diiodide (Me(2)SiSiMe(2))eta(5)-C(5)H(4)Fe(CO)(2)I](2) (2) with retention of the Si-Si bond. When excess (2-4 equiv) I(2) was used to react with 1 in either benzene or chloroform, iodonium-bridged diiron complex (Me(2)SiSiMe(2))eta(5)-C(5)H(4)Fe(CO)(2)](2)I(+)](I(5)(-)) (4) was obtained, in which the Si-Si bond was still retained. It is noteworthy that 4 contains a counteranion I(5)(-) rather than the expected I(3)(-), which is the first example for an iodonium-bridged diiron complex to combine a polyiodide anion larger than I(3)(-). UV irradiation of 2 did not affect the stability of the silicon-silicon bond and, in the presence of PR(3), resulted in CO substitution to give (Me(2)SiSiMe(2))eta(5)-C(5)H(4)Fe(CO)(PR(3))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) A] is about the same as that of 1 2.346(4) A], 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) degrees. Of particular interest is the observation that the I(5)(-) anions of 4 are self-assembled into novel layered, two-dimensional networks with the (Me(2)SiSiMe(2))eta(5)-C(5)H(4)Fe(CO)(2)](2)I(+) cations as the template.