A mononuclear cyclopentadiene-iron complex grafted in the supercages of HY zeolite: synthesis, structure, and reactivity

The reaction of ferrocene with the acidic hydroxy groups in the supercages of zeolite HY dehydrated at 673 K and the reactivity of the resultant surface species towards CO and O(2) were investigated by temperature-programmed decomposition (TPD) and reduction (TPR) and IR, X-ray absorption fine structure analysis (XAFS), and X-ray photoelectron (XP) spectroscopy. In situ FTIR, TPD, TPR, and chemical analysis reveal that the Cp(2)Fe molecule adsorbed on the zeolite surface loses one cyclopentadienyl group under vacuum at 423 K, which leads to the formation of a well-defined mononuclear surface Fe-C(5)H(6) complex grafted to two acidic sites and one (triple bond]Si-O-Sitriple bond]) unit, as confirmed by the lack of Fe-Fe contributions in the EXAFS spectra. Each iron atom is coordinated, on average, to three oxygen atoms of the zeolite surface with a Fe--O distance of 2.00 A and to five carbon atoms with a Fe--C distance of 2.09 A. IR spectra indicate that the cyclopentadiene-iron species grafted on the surface of the zeolite is quite stable in vacuo or under an inert or hydrogen atmosphere below 423 K, and is also relatively stable under oxygen at room temperature. However, the cyclopentadiene ligand readily reacts with CO to form a compound containing carbonyl at 323 K, and even at room temperature. The single carbonyl band in the IR spectra provides evidence for the nearly uniform formation of a cyclopentadiene-iron species on the surface of the zeolite.