INFRARED SPECTROSCOPIC STUDIES OF REACTIONS OF IRON ATOMS WITH CYCLIC HYDROCARBONS IN ARGON MATRICES

[摘要] Iron vapors were cocondensed with various cyclic hydrocarbons in excess argon and the FTIR matrix spectra were measured. For mixtures of iron and cyclopentadiene in argon, a spontaneous reaction occurred to form cyclopentadienyliron hydride, the first cyclopentadienyl transition metal hydride ever observed. On condensation of iron with benzene, complexes of various stoichiometry were formed. Photolysis of these complexes did not lead to any oxidative-addition production. Depositing iron with cycloheptatriene in excess argon led to the formation of an adduct, which upon photolysis of UV light rearranged to form a simple bond-insertion product, cycloheptatrienyliron hydride; no evidence was seen for the formation of the aromatic tropylium cation, C$sb 7$H$sb {7}sp{+}$. When the two isomers of cyclohexadiene (CHD) were codeposited with iron, adducts were formed for both isomers. Upon photolysis with UV light, the monoiron-CHD adducts rearranged in a dehydrogenation reaction, forming FeH$sb 2$ and benzene. These results were confirmed by comparison with the iron/benzene codeposition studies. There was also evidence for the diiron-CHD adducts reacting upon photolysis with visible light; this is the first indication of C-H bond activation by iron dimers. In these cases, deuterium substitution of the organic compound was used to obtain substantiating evidence of C-H bond activation. Iron was codeposited with cubane, a highly strained cyclic hydrocarbon. Despite its high strain energy, cubane showed no indication of reaction towards iron atoms in argon matrices, even upon UV photolysis. This is a dramatic testimony to the kinetic stability of the cubane molecule once it is formed. Iron has also been reacted with methylenecyclopropane in argon matrices; preliminary findings are that iron causes MCP to decompose to ethylene and some other hydrocarbon fragment; UV photolysis causes the formation of two different photoproducts. While conclusive identification of these photoproducts has not been established, suggestions can be advanced based on the infrared absorptions of the photoproducts.

[发布机构] Rice University