Photochemistry bridged

C5Me5) was stable up to room temperature (108,109). A surprising feature of the matrix photochemistry (6,7) was that only the trans isomer of [CpFe(CO)2]2 was photolyzed, and it may be that this was the consequence of concerted CO loss from the trans isomer and isomerization to form the triply bridged product (6). 

Another dinuclear carbonyl which presents interesting problems is ](ri C5H5)Fe(CO) ] 2 Does the photochemistry proceed exclusively through homolytic fission to produce two (13 -05 )Fe-(C0)2 radicals or by other possible routes The discussion of this reaction has involved mechanistic and synthetic studies (77), flash photolysis (78) and low-temperature photolysis (29) - the latter work, in THF or ethyl chloride at -78°C, invokes an intermediate in which the Fe-Fe direct bond is broken but the two halves of the molecule are held together by a CO bridge. Clearly such an intriguing problem merits more detailed investigations. 

There have been remarkable advances in synchrotron radiation research and related experimental techniques in the range from the vacuum ultraviolet radiation to soft X-ray, where the most important part of the magnitudes of these cross-section values is observed, as shown below. Therefore, it is also concluded that synchrotron radiation can bridge a wide gap in the energy scale between photochemistry and radiation chemistry. Such a situation of synchrotron radiation as a photon source is summarized in Fig. 1 [5,6]. 

For example, in 1963 the photochemistry of magnesium phthalocyanine with coordinated uranium cations was studied in pyridine and ethanol and indicated the occurrence of PET to the uranium complex . A rapid photoinduced electron transfer (2-20 ps) followed by an ultrafast charge recombination was shown for various zinc and magnesium porphyrins linked to a platinum terpyridine acetylide complex . The results indicated the electronic interactions between the porphyrin subunit and the platinum complex, and underscored the potential of the linking para-phenylene bisacetylene bridge to mediate a rapid electron transfer over a long donor-acceptor distance. 

Substituted benzenes have been shown to undergo various valence photoisomerizations to yield bicyclo[2.2 Ojhexadienes, benzvalenes, and prismanes.223 The photochemistry of benzene itself is, at present, rather ill defined. Recently, it has been shown that benzene excited by 2537-A irradiation adds to olefins224-226 and to dienes227 to form 1,2-, 1-3-, and 1,4-bridged products. 

The formation of the unsaturated intermediate Run(OEP) from the hydrido-complex RumH(OEP) is supposed to occur from a LMCT excited state. As a consequence, the dimeric [RuH(OEP)]2 with a metal-metal interaction is formed [245]. Irradiation of some systems containing Fein(Por)N3 leads to p-nitrido bridged binuclear mixed-valence complexes [(Por)Fem-N-Fe,v(Por)] [134, 162], In both cases photochemistry was used as a conventional preparative route for synthesis of the binuclear complexes. 

The photochemistry of [Cp(C0)20s]2 has been examined recently by two separate groups. Bitterwolf and coworkers illustrated that photolysis of the complex in nujol at low temperature resulted in loss of CO and formation of a triply CO bridged species (Fig. 16). In benzene solution at room tempera-... 

In the meanwhile, interdisciplinary research became more and more essential and photochemistry became a perfect example as a powerful bridge between chemistry, physics, and biology, between material science, life science, and synthesis. 

Firth S, Hodges PM, Poliakoff M, Turner JJ. Comparative matrix isolation and time-resolved infrared studies on the photochemistry of MnRe(CO)10 and Re2 (CO)10 evidence for CO-bridged MnRe(CO)9. Inorg Chem 1986 25(25) 4608-4610. 

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