Transition metal germylene complexes in zeolite cages: anchoring and stability

Abstract

The surface chemistry of the two germylene complexes Cl{sub 2}(THF)GeM(CO){sub 5} (M = Mo (1) and W (2)) in zeolite Y was studied with X-ray absorption spectroscopy (Ge, Mo, W edge EXAFS) and in situ FTIR/TPD-MS techniques. The molybdenum complex 1 interacts with the framework of Na-Y zeolite at room temperature where decarbonylation occurs to a small extent. The intrazeolite 1 retains the Ge-Mo bond is retained up to about the same temperature. At higher temperatures, the Ge-Mo bond is cleaved and MoCl{sub d} and Mo-Mo species are formed in the Na-Y and H-Y forms, respectively. GeCl{sub x} fragments attach to both zeolite frameworks. The intrazeolite complex Cl{sub 2}(THF)GeW(CO){sub 5} (2) retains all five carbonyl ligands up to about 100 {degrees}C in both Na-Y and at about 80 {degrees}C in the proton form. The intrazeolite stability of the anchored Ge-W complex is somewhat higher than that of the Ge-Mo analog, and WCl{sub x} species are formed upon cleavage of the Ge-W bond at higher temperatures. The anchoring of the Cl{sub 2}(THF)Ge moiety into Na-Y is believed to be based upon a Na{sup +}--Cl{sup -} interaction between Na ions in zeolite coordination sites and the chloride ligands of the precursor. Themore » only gas evolution detected up to about 120 {degrees}C is due to partial decarbonylation (CO) and HCl formation in the acid supports. The absence of precursor desorption confirms the effective anchoring of the transition-metal germylene complexes into zeolite cages. 39 refs., 16 figs., 6 tabs.« less