Switching from Ru to Fe: picosecond IR spectroscopic investigation of the potential of the (fulvalene)tetracarbonyldiiron frame for molecular solar-thermal storage.

A foray into the exploration of Fe analogues of the (fulvalene)tetracarbonyldiruthenium [FvRu2(CO)4] solar-thermal storage system 1⇆2 is described. It was facilitated by the development of a convenient synthetic access to the parent [FvFe2(CO)4] 3a and the more soluble di(tert-butyl)fulvalene derivatives 3c and d. Laboratory time scale irradiations (>400 nm) fail to induce photoisomerization, an observation that is explained by the results of time-resolved IR experiments. They show that photoexcitation generates only the short-lived singlet syn biradical of 3 (and a small amount of decarbonylation product), in the absence of the corresponding triplet species required for the occurrence of rearrangement to 4.