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A series of new structural variants of the Si-Si bridged bis(cyclopentadienyl)tetracarbonyldiiron complex (η 5 ,η 5 -C 5 H 4 XC 5 H 4 )Fe 2 (CO) 4 , where X ) MeSi[µ-(CH 2 ) 4 ]SiMe (3), CH 2 SiMe 2 (7), and SiMe 2 SiPh 2 (10), were synthesized and their properties studied with emphasis on the thermal rearrangement that had been demonstrated to occur when X ) SiMe 2 SiMe 2 . It was found that the presence of the cyclic structure on the Si-Si bridge for complex 3 prohibited the thermal rearrangement, but oxygen insertion into the Si-Si bond took place under thermal conditions to give the new Si-O-Si bridged complex {η 5 ,η 5 -C 5 H 4 MeSi(µ-O)[µ-(CH 2 ) 4 ]SiMeC 5 H 4 }Fe 2 (CO) 4 (4). Using CH 2 SiMe 2 as the bridging group in complex 7 also resulted in failure of the rearrangement because the C-Si bond could not be activated by the iron center. Complex 10, with the unsymmetric bridging group SiMe 2 SiPh 2 , underwent thermal rearrangement, producing the expected product cyclic-[(Me 2 Si-η 5 -C 5 H 4 )Fe(CO) 2 (Ph 2 Si-η 5 -C 5 H 4 )Fe(CO) 2 ]-( 11) with two Si-Fe bonds. When the reaction was performed in the presence of P(OPh) 3 , incorporation of the phosphite ligand in the rearranged product took place, providing two regioisomers, cyclic-{(Me 2 Si-η 5 -C 5 H 4 )Fe(CO)[P(OPh) 3 ](Ph 2 Si-η 5 -C 5 H 4 )Fe(CO) 2 }-(12a) and cyclic-{(Me 2 Si-η 5 -C 5 H 4 )Fe(CO) 2 (Ph 2 Si-η 5 -C 5 H 4 )Fe(CO)[P(OPh) 3 ]}-(12b), in a 1:1.8 ratio. The reaction of 10 with I 2 led to Fe-Fe bond cleavage, affording di-iodide (η 5 ,η 5 -C 5 H 4 Me 2 SiSiPh 2 C 5 H 4 )[Fe(CO) 2 I] 2 (13). The molecular structures of 3, 4, 7, 10, 11, and 13 have been determined by X-ray diffraction methods.

Intramolecular actiVation of the Si-Si bond linked to an η 4 -silole ligand by a metal center was obserVed when 1,1-bis(trimethylsilyl)tetraphenylsilole was heated with Fe(CO) 5 in refluxing p-xylene, to produce η 4 -(1-trimethylsilyl-1-methyltetraphenylsilole)Fe(CO) 3 as the final product.Si-Si bonds are very thermally stable, sometimes even comparable to a C-C bond, but can easily be activated by transition metals. 1,2 This property has most frequently been observed in intramolecular processes, which has led to many intriguing reactions in recent years. [3][4][5][6][7][8][9] To date, many studies of such reactions have focused on systems containing Si-Si bonds directly linked to transition metals, initially observed independently by Pannell's and Ogino's groups in 1986. 4,5 Also studied have been systems in which the Si-Si bonds are linked indirectly to a metal atom through an η 1 -methylene ligand, a

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