ic011252j_si_002.pdf (53.19 kB)
Synthesis of Heterometallic Bismuth/Molydenum Alkoxides and Their Behavior on Silica Surfaces§
journal contribution
posted on 2002-06-01, 00:00 authored by Christian Limberg, Marc Hunger, Wilhelm Habicht, Elisabeth KaiferThe reaction of [(C3H5)Mo(CO)2(CH3CN)2Cl], 2, with [Bi(OCH2CH2OCH3)3]2 on a large scale leads to the novel
molybdenum/bismuth alkoxide [(C3H5)Mo(CO)2(μ-κO,2κO‘-OCH2CH2OCH3)2(μ-κO-OCH2CH2OCH3)BiCl], 6, as the
main product as well as to [(C3H5)Mo(CO)2(μ-κO,2κO‘-OCH2CH2OCH3)2(μ-Cl)BiCl], 4, as a byproduct. Both
compounds were characterized by elemental analysis, IR, and NMR spectroscopy as well as by X-ray diffraction.
If 6 is brought into contact with a large excess of silica gel, aggregation and condensation reactions are initiated,
which led to clusters of ca. 200 nm size spread over the silica surface. When the resulting material is calcinated
at 350 °C in the presence of O2, all organic ligands are eliminated and the metal oxo units rearrange: SEM/EDX
measurements showed afterward Mo-free bismuth oxo clusters with sizes between 30 and 1000 nm, which are
distributed together with molybdenum oxo particles of lower nuclearity over the silica surface. If such a material is
employed as a potential catalyst for the propene oxidation under technical conditions, no activity is observed. If,
however, the process is performed under very low pressures, a conversion of 5% is found. This result is discussed
in the context of the mechanism proposed for the technical oxidation of propene to acrolein on bismuthmolybdate
catalysts.