REACTIONS OF ATOMIC AND DIATOMIC IRON WITH ALLENE IN SOLID ARGON

The activation of the C-H bond of allene or propadiene by ground-state atomic iron has been observed in solid argon at 10 K. The new matrix-isolated product, propadienyliron hydride, was characterized via FTIR spectroscopy. The photochemistry of the metal atom and allene was studied and revealed the isomerization of allene into propyne via the formation of the sigma-bonded iron propyne complex Fe(HC=CCH3). The latter underwent interestings and rich photochemistry (which will be treated in greater detail in a future publication) with the activation of the methyl and acetylenic C-H bonds as well as the C-C single bond of HC=CCH3. In contrast, diatomic iron exhibited different reactivity toward allene, with the formation of pi-complexes that did not photorearrange to a C-H-activated product. Evidence based on FTIR spectroscopy indicates that diatomic iron is simultaneously bonded to the two pi-bonds of allene, forcing the latter into a V-shaped structure for Fe2(H2C=C-H-2). Isotopic studies with D2C=C=CD2 support these findings.