Ring-Functionalized Molybdenocene Complexes

The synthesis and characterization of new ring-functionalized molybdenocene derivatives [CpCp′Mo(CO)2]2+ and [CpCp′Mo(CO)Br]+ (η5-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 II 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(η5-C5H4CH2CH2COOEt)(CO)2][MoOBr4(H2O)][Br], [(η5-C5H4COOMe)Mo(η3-C3H5)(CO)2], [(η5-C5H4COOMe)Mo(CO)2(NCMe)2][BF4], [(η5-C5H4SiMe3)Mo(CO)2(NCMe)2][BF4], and [CpMo(η5-C5H4COOMe)(CO)H][BF4] were determined with X-ray diffraction analysis.