Synthesis and properties of structural variants of the Si-Si bridged bis(cyclopentadienyl)tetracarbonyldiiron complexes: Modification on the bridge

A series of new structural variants of the Si-Si bridged bis(cyclopentadienyl)tetracarbonyidiiron complex (eta(5),eta(5)-C5H4XC5H4)Fe-2(CO)(4), where X = MeSi[mu-(CH2)(4)]SiMe (3), CH2SiMe,) (7), and SiMe2SiPh2 (10), were synthesized and their properties studied with emphasis on the thermal rearrangement that had been demonstrated to occur when X = SiMe2SMe2. 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 {eta(5) ,eta(5)-C5H4MeSi(mu-O)[mu-(CH2)(4)]SiMeC5H4)Fe-2(CO)(4) (4). Using CH2SiMe2 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 SiMe2SiPh2, underwent thermal rearrangement, producing the expected product cyclic-[(Me2Si-eta(5)-C5H4)Fe(CO)(2)(Ph2Si-eta(5)-C5H4)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-{(Me2Si-eta(5)-C5H4)Fe(CO)[P(OPh)(3)](Ph2Si-eta(5)-C5H4)Fe(CO)(2)]-(12a) and cyclic-{[(Me2Si-eta(5)-C5H4)Fe(CO)(2)(Ph2Si-eta(5)-C5H4)Fe(CO)[P(OPh)(3)]}-(12b), in a 1:1.8 ratio. The reaction of 10 with 12 led to Fe-Fe bond cleavage, affording di-iodide (eta(5), eta(5)-C5H4Me2SiSiPh2C5H4)[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.