Photochemistry of some iron and ruthenium (η⁵-cyclopentadienyl) carbonyl dimers in frozen gas matrices at ca. 12 K

Abstract

The photochemistry of [M,(q5-C,H,) ,(CO),][M = Fe, (1); or Ru, (2)] and [CH,{(q5-C,H,)M(C0), },] [M = Fe, (5); or Ru, ( 6)] has been studied in frozen-gas matrices (Ar, CH, , and N, ) at ca. 12 K and that of (2) in poly(viny1 chloride) (pvc) films at ca. 12 K. Low-energy photolysis of compounds (1) and (2) was found to induce opening of trans-carbonyl-bridged species affording terminal carbonyl species. Photolyses into the electronic absorption band maxima of these new terminal-carbonyl species yielded 17-electron radical species [ M(q5-C,H,) (CO),]' as well as small amounts of triply carbonyl-bridged species, [M,(q5-C5H5),(p-C0),1. At the corresponding maxima of trans-carbonyl-bridged complexes (1 ) and ( 2) photolysis yielded the triply-carbonyl-bridged species directly. Photolysis of (5), which is exclusively bridging and is constrained by the methylene linkage between the rings to be in a cis conformation, at a range of wavelengths showed no evidence for carbonyl-bridge opening. At its electronic absorption maxima photolysis resulted in carbonyl ejection and formation of a new species whose spectrum is consistent with its having three terminal carbonyl groups and an Fe-Fe double bond. Photolysis of compound (6) which exists in a cis-terminal conformation also resulted in carbonyl loss and formation of a species similar to that observed for (5). These results are discussed in terms of their relationship to previous photochemical studies of (1) and ( 2) and an overall model for the photochemical behaviour of (1) and (2) is presented.

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

“…The non-radical pathway was reported to proceed only from the trans-b form upon long wavelength (l irr >475 nm) irradiation [52]. This is consistent with the domination of the absorption of the trans-b and trans-nb isomers within this radiation range (cf.…”

“…Contrary to the previous reports [34,52,69], in recent studies no photochemical dissociation of the terminal CO ligand was identified. Instead the cleavage of Ru-CO bridged and Ru-Ru bonds was recognized to follow the excitations at 265 and 330 nm of II-b and II-nb, respectively (paths a and b in Scheme 1) [3,68,69].…”

“…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].…”

Binuclear Complexes of Ruthenium and Osmium Containing Metal Metal Bonds

“…On the other hand, photolysis of the latter resulted (154) in carbonyl loss and the formation of a new species whose spectrum is consistent with it having three terminal carbonyl groups and an Ru-Ru double bond. 291 Photolysis of [Ru 2 Cp* 2 (u-CO) 2 (CO) 2 ] under an atmosphere of hydrogen results in the production of red crystalline [Ru 2 Cp* 2 (u-H) 2 (CO) 2 ] (156) and yellow crystalline [Ru 2 Cp* 2 (u-H) 2 (jn-CO)] (157)* in ca. 10% yield each.…”

X‐ray Transient Absorption and Picosecond IR Spectroscopy of Fulvalene(tetracarbonyl)diruthenium on Photoexcitation

“…Specifically, there are two sets of kinetically correlated peaks: one (D) comprising signals at 1945, 1995, and 2010 cm À1 , decaying with a time constant of about 30 ps, and a second (E), composed of bands at 1933 and 1970 cm À1 and more persistent, up to about 2 ns ( Figure 5). [11] The considerably weaker intensity of absorptions corresponding to E suggests that the primary pathway for the decay of D is to reform 1 b, although relaxation to the more stable triplet E is a likely competing pathway. [6,10] Since this behavior rules out the creation of tert-butyl B (which should go on to 2 b; Figure 1), and guided by the XTA data, we assign the entity with the faster decay to a singlet syn biradical photoproduct D, and the other to its long-lived triplet relative E. For comparison, the analogous near-UV photolysis (> 375 nm) of [CpRu(CO) 2 ] 2 produces the CpRu(CO) 2 radical with IR bands at 1930 and 2000 cm À1 .…”