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Fluorinated alkoxide ligands RO(-) (R=CH(CF3 )2 ) are the key to the isolation of compounds of the type [Cp2 Mo(OR)2 ]. When electron-donating groups R are employed, the Mo(OR)2 moiety can, and necessarily has to, serve as a ligand for Lewis acidic fragments, allowing the isolation and structural characterization of the first heterodimetallic alkoxide containing a Bi and a Mo center (1).

Reaction of [((CH 3 )C 3 H 4 )Mo(CO) 2 (CH 3 CN) 2 Cl], 2, with [Bi(OEt) 3 ] x provides the heterotetranuclear complex [((CH 3 )C 3 H 4 )Mo(CO) 2 (µ-OEt) 3 Bi(µ-OEt) 2 Bi(µ-OEt) 3 Mo(CO) 2 ((CH 3 )-C 3 H 4 )], 3, in good yields. If 2 is reacted with [Bi(OCH 2 CH 2 OCH 3 ) 3 ] 2 , a dinuclear chloro alkoxide [((CH 3 )C 3 H 4 )Mo(CO) 2 (µ-κO,2κO′-OCH 2 CH 2 OCH 3 ) 2 (µ-Cl)BiCl], 4, is obtained, while pretreatment of 2 with AgBF 4 and subsequent reaction with [Bi(OCH 2 CH 2 OCH 3 ) 3 ] 2 leads to the chloride-free complex [((CH 3 )C 3 H 4 )Mo(CO) 2 (µ-κO,2κO′-OCH 2 CH 2 OCH 3 ) 3 Bi(thf)][BF 4 ], 6, with a Bi center surrounded by seven oxygen donors. All compounds have been characterized by NMR and IR spectroscopy as well as elemental analysis, and their crystal structures were determined by means of single-crystal X-ray diffraction. 3, 4, and 6 belong to the few compounds known (there is only one other precedent) where Mo and Bi centers are bridged by oxygen-containing ligands and can therefore be considered as cornerstones on the way to the synthesis of yet unknown molecular compounds with Mo-O-Bi functions resembling those occurring on the surface of nMoO 3 -Bi 2 O 3 catalysts.

The reaction of [(C(3)H(5))Mo(CO)(2)(CH(3)CN)(2)Cl], 2, with [Bi(OCH(2)CH(2)OCH(3))(3)](2) on a large scale leads to the novel molybdenum/bismuth alkoxide [(C(3)H(5))Mo(CO)(2)(mu-kappa O,2 kappa O'-OCH(2)CH(2)OCH(3))(2)(mu-kappa O-OCH(2)CH(2)OCH(3))BiCl], 6, as the main product as well as to [(C(3)H(5))Mo(CO)(2)(mu-kappa O,2 kappa O'-OCH(2)CH(2)OCH(3))(2)(mu-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 degrees C in the presence of O(2), 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.

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