Stepwise Photochemical CO Loss from Cp2Fe2(CO)2(.mu.-CO)2 in Low-Temperature Matrixes: Evidence for an Unsupported Fe-Fe Triple Bond

Organometallic photochemistry at the end of its first century

“…The photochemical transformation from triplet (terminal) to singlet (bridged) forms of Cp 2 Fe 2 (CO) 2 observed by Bursten and his coworkers is one such example [99]. Matrix studies unfortunately tell nothing about the lifetimes of observed species or their possible role in observed reactions.…”

Theoretical studies on the high-spin binuclear cyclopentadienyliron derivatives Cp2Fe2(CN)n(Cp = η5-C5H5;n= 6, 5, 4, 3, 2, 1)

“…The Fe-Fe distance in 2CN-1T is predicted to be ∼2.6 Å in accord with the single bond required to give each iron atom a 17-electron configuration, consistent with the triplet electronic state. For a comparison, the dicarbonyl Cp 2 Fe 2 (CO) 2 is an unbridged isomer, prepared by the photolysis of Cp 2 Fe 2 (CO) 4 in low-temperature matrices [16].…”

“…Vahrenkamp et al [9] obtained the binuclear complex [Cp(CO) 2 Fe-CN-Fe(dppe)Cp](PF 6 ) 2 showing the paramagnetism due to one unpaired electron. A high-spin methyl isocyanide complex [Cp * Fe(MeCN) (dippe)][BPh 4 ] (Cp * = η 5 -C 5 Me 5 ; Me = CH 3 ; dippe = 1,2-bis(diisopropylphosphino)ethane) [10], which can be obtained directly from Fe(II) complex with two unpaired electrons, and the effective magnetic moment (4.0 μ B ) is greater than that of the paramagnetic, 18-electron complex [Cp * Fe(Me 2 CO)(dppe)][CF 3 SO 3 ] [11] For the binuclear cyclopentadienyliron derivatives, it has been found that some carbonyl derivatives are stable, such as Cp 2 Fe 2 (CO) 4 [13], Cp 2 Fe 2 (CO) 3 [14], Cp * 2 Fe 2 (CO) 3 [15], Cp 2 Fe 2 (CO) 2 [16] and Cp * 2 Fe 2 (CO) 2 [17]. The tricarbonyl Cp 2 Fe 2 (CO) 3 [13], with a Fe-Fe double bond, has been predicted to exhibit paramagnetism consistent with a triplet electronic state, indicating that its Fe-Fe double bond is analogous to the double bond in dioxygen.…”

Structure, Spectroscopy and Photochemistry of the [M(η5-C5H5)(CO)2]2 Complexes (M=Fe, Ru)

“…The alkyne coordination, leading to formation of a transient [Cp 2 Fe 2 (CO) 3 (RCϵCR)] species, followed by intramolecular transformations, was also reported [51]. The nature of the [Cp 2 Fe 2 (CO) 3 ] intermediate has been discussed in the literature and was postulated to be triply [52][53][54][55][56][57][58], doubly [59] or singly CO-bridged [59]. Recently the photogenerated CO-loss intermediate was studied by time-resolved IR spectroscopy and its triply bridged structure was proved [60].…”

“…Recently the photogenerated CO-loss intermediate was studied by time-resolved IR spectroscopy and its triply bridged structure was proved [60]. Extended irradiation of the solution leads to the loss of further CO ligand and formation of [Cp 2 Fe 2 (CO) 2 ] with a triple Fe-Fe bond [58,61].…”