Carbonyliron-olefin photochemistry: quantum yields for the sequential substitution of two carbonyl groups in pentacarbonyliron by (E)-cyclooctene. Synthesis of the first stable (.eta.2-olefin)3Fe(CO)2 complex

Abstract

Multiple photosubstitution of CO groups in pentacarbonyliron by an olefin has been investigated by using (E)-cyclooctene as a model olefin exhibiting exceptional coordination properties. The quantum yields {Phi}{sub 1} and {Phi}{sub 2} for sequential conversion of Fe(CO){sub 5} into ({eta}{sup 2}-(E)-C{sub 8}H{sub 14})Fe(CO){sub 4} (1) and ({eta}{sup 2}-(E)-C{sub 8}H{sub 14}){sub 2}Fe(CO){sub 3} (2), respectively, when evaluated using the appropriate formalism for internal light filter corrections (presented in detail in the Appendix), are found to be constant up to high conversion: {Phi}{sub 1} = 0.80 at 302 nm and 0.77 at 254 nm, {Phi}{sub 2} = 0.59 at 302 nm and 0.82 at 254 nm. The wavelength dependence of {Phi}{sub 2} is interpreted in terms of 2 different ligand field excited states of 1, providing for varying CO vs olefin photodetachment. The overall quantum yield for the generation of 2 from Fe(CO){sub 5} (ca. 0.20 at 60% conversion of pentacarbonyliron) is discussed in the context of carbonyliron photocatalyzed olefin isomerization, which is known to involve (labile) ({eta}{sup 2}-olefin){sub 2}Fe(CO){sub 3} as the active catalyst. The synthesis of ({eta}{sup 2}-(E)-C{sub 8}H{sub 14}){sub 3}Fe(CO){sub 2} (3), which is the first isolated representative of this type of complex, is achieved by irradiation of 2more » in the presence of excess (E)-cyclooctene, whereby liberated CO is required to be rigorously removed by an inert-gas stream.« less