Reactions of cyclopentadienylmolybdenum compounds with bismuth alkoxides

Abstract

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 [CpMoCl 4] with [Bi(OEt) 3] x did not yield a tractable product, its reaction with [Bi{OCH(CF 3) 2} 3(THF)] 2 ( 6), led to the isolation of [CpMoCl{OCH(CF 3) 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 [Cp 2MoH 2] with 6. Elimination of HOCH(CF 3) 2 provided [Cp 2Mo(Bi{OCH(CF 3) 2} 2) 2] ( 8), containing two MoBi bonds as revealed by a single-crystal X-ray structure analysis. The oxidation of 8 with t BuOOH gave rise to the formation of the molybdocene alkoxide [Cp 2Mo{OCH(CF 3) 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.