The synthesis and characterization of new ring-functionalized molybdenocene derivatives [CpCp'Mo(CO)(2)](2+) and [CpCp'Mo(CO)Br](+) (eta(5)-C5H4R; R = CH2CH2OMe, CH2CH2COOEt, CH2CH2OOCMe, COOMe) are reported. Three alternative routes were used to assemble the CpCp'Mo moiety. Following route I, the unsubstituted precursor [CpMo(CO)(2)(NCMe)(2)](+) reacts with substituted cyclopentadienes (Cp'H) to give after oxidation dicationic compounds [CpCp'Mo(CO)(2)](2+). Alternatively, route II introduces the substituent in the first reaction step upon the synthesis of [Cp'Mo(CO)(2)(NCMe)(2)](+). In this case, the bis-cyclopentadienyl compounds [CpCp'Mo(CO)(2)](2+) were obtained after reaction with cyclopentadiene (C5H6) and subsequent oxidation. The NMR spectroscopic measurements prove that the reaction pathways of routes I and 11 go through different intermediates. The bromo complexes [CpCp'Mo(CO)Br](+) were synthesized using route III. Reaction of [Cp'Mo(CO)(2)(NCMe)(2)](+) with C5H5SiMe3 gives hydride complexes [CpCp'Mo(CO)H](+). Appropriate bromo complexes were obtained upon reaction with bromine. The ring-functionalized bis-cyclopentadienyl molybdenum(IV) compounds and their monocyclopentadienyl precursors were characterized by spectroscopic methods. Structures of [CpMo(eta(5)-C5H4CH2CH2COOEt)(CO)(2)][MoOBr4(H2O)][Br], [(eta(5)-C5H4COOMe)Mo(eta(3) -C3H5)(CO)(2)], [eta(5)- C5H4COOMe)Mo(CO)(2)(NCMe)(2)][BF4], [(eta(5)-C5H4SiMe3)Mo(CO)(2)(NCMe)(2)[BF4], and [CpMo(eta(5)-C5H4COOMe)(CO)H][BF4] were determined with X-ray diffraction analysis.