Chemistry of the Si-Si and Fe-Fe bonds in the cyclic structure (Me2SiSiMe2)[eta(5)-C5H4Fe(CO)(2)](2). Selective cleavage of the Fe-Fe bond by I-2 and unexpected properties of the iodide

摘要

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 (Me2SiSiMe2)[eta(5)-C5H4Fe(CO)(2)I](2) (2) with retention of the Si-Si bond. When excess (2-4 equiv) 12 was used to react with 1 in either benzene or chloroform, iodonium-bridged diiron complex {(Me2SiSiMe2)[eta(5)-C5H4Fe(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 13, 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 PR3, resulted in CO substitution to give (Me2SiSiMe2)[eta(5)-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) Angstrom] is about the same as that of 1 [2.346(4) Angstrom], 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 (Me2SiSiMe2)[eta(5)-C5H4Fe(CO)(2)](2)I+ cations as the template. [References: 24]