We report on the preparation and spectroscopic properties of complexes of the general formula MoBr 2 O 2 L n with L=NCCH 3 (n=2), NCC(CH 3 ) 3 (n=1), NCC 6 H 5 (n=2). The complex MoBr 2 O 2 (CH 3 CN) 2 is additionally examined by single crystal X-ray structure determination. The MoBr 2 O 2 L n complexes are very electron deficient ( 1 7 O-, 9 5 Mo-NMR evidence) and readily react with electron donor N-ligands to give more stable complexes e.g. MoBr 2 O 2 (bipyrimidine). The structure of the latter compound has been determined by single crystal X-ray crystallography. Reactions with organometallic complexes of the type [Cp'Mo(CN) 2 (CO) 2 ]K (Cp'=Cp or Cp*) and Cp(CO) 2 Fe(CN) or [Cp(CO)Fe(CN) 2 ]K result in the immediate reduction of the Mo(VI) center, as shown by EPR spectroscopy. The MoBr 2 O 2 L n complexes are catalysts for the epoxidation of cyclooctene but decompose slowly during the course of the reaction due to their pronounced moisture sensitivity.