Reactions of cyclopentadienylmolybdenum compounds with bismuth alkoxides

The unique ability of bismuthmolybdate phases to act as heterogeneous catalysts for the oxidation of olefins stimulates research focussing on molecular Bi/Mo complexes, and in this context the behaviour of cyclopentadienyl molybdenum compounds in the presence of bismuth alkoxides has been investigated. While the reaction of [CpMoCl4] with [Bi(OEt)(3)](x) did not yield a tractable product, its reaction with [Bi{OCH(CF3)(2)}(3)(THF)](2) (6), led to the isolation of [CpMoCl{OCH(CF3)(2)}(3)] (7), formed in a halide/alkoxide exchange reaction. The crystal structure of 7 is discussed. A heterometallic Mo/Bi complex could be obtained via treatment of [Cp2MoH2] with 6. Elimination of HOCH(CF3)(2) provided [Cp2Mo(Bi{OCH(CF3)(2)}(2))(2)] (8), containing two Mo-Bi bonds as revealed by a single-crystal X-ray structure analysis. The oxidation of 8 with 'BuOOH gave rise to the formation of the molybdocene alkoxide [Cp2Mo{OCH(CF3)(2)}(2)] in good yields, i.e. the Mo-Bi bonds were cleaved in a formal four-electron oxidation process - possibly via the intermediate formation of Mo-O-Bi moieties. To test for any intermediate and its in situ reactivity, the same reaction was also performed in the presence of an excess of cis-stilbene. It turned out that 8 behaved as an efficient catalyst for the epoxidation of this olefin. (C) 2002 Elsevier Science B.V. All rights reserved.