No abstract

the intermediate formation of species II, because coordination of CO to the vacant coordination site in II would compete with coordination of PR3 at the site and the quantum yield would decrease. The quantum yield data in Table I show that the CC14 photoreaction becomes more efficient relative to the PR3 photoreaction as the irradiation wavelength decreases. This result is entirely reasonable in the context of our proposal of two reaction channels, because relatively more radicals should be formed from the more energetic excited states.The finding that the long-lived intermediate generated by flash photolysis reacts with CC147 coupled with our discovery that CC14 reacts with III to give only CpFe(CO)2Cl establish that it is not necessary to postulate 17-electron fragment intermediates as primary photoproducts based only on an observation that a chlorine abstraction product forms. In our scheme the chlorocarbon could react directly either with II or III (in the latter case by displacing phosphine) to give CpFe(CO)2Cl, thereby explaining why CpFe(CO)2Cl is the only product in the photolysis of Cp2Fe2(CO)4 with equimolar amounts of CC14 and PR3. However, the fact that 6 atm of CO does not markedly inhibit the reaction with CC14 suggests that the reaction of II with chlorocarbons is not very efficient compared to the radical pathway.The relatively long-lived photoproduct observed by Caspar and Meyer was proposed7 to be Cp2Fe2(CO)3, formed by Fe-CO bond dissociation. This particular photoproduct absorbs strongly in the visible, and it reacts with CO and other ligands. Because II should have a visible absorption band attributable to charge-transfer excitation from the coordinatively saturated iron to the 16-electron ("CpFeCO") center,20 the flash photolysis results7 can be accommodated equally well in terms of our mechanistic scheme.