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 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 )[η 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 )[η 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 )[η 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)°. 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 )[η 5 -C5H4Fe(CO) 2 ] 2 I + cations as the template.