Mass spectra of organometallic compounds: XIV—Some monometallic olefing manganese tricarbonyl derivatives

The metastable ion supported fragmentation process in the mass spectra of the cyclohexadienyl derivative C₆H₇Mn(CO)₃, the cycloheptadienyl derivative C₇H₉Mn(CO)₃, the 1,2,3,4,5-and 1,2,3,5,6-pentahaptocyclootadienyl derivatives C₈H₁₁Mn(CO)₃, the cyclooctatrienyl derivative C₈H₉Mn(CO)₃ and the substituted cyclopentadienyl derivative (CH₃)₂NCH₂C₅H₄Mn(CO)₃, are described. Losses of carbonyl groups, generally stepwise, from the molecular ions to give the corresponding M – 3CO]⁺· ions are first observed. Further fragmentation of the carbonyl-free M – 3CO]⁺· ions can involve a variety of processes such as the following: (a) elimination of a neutral manganese atom to give a hydrocarbon fragment; (b) elimination of a neutral hydrocarbon fragment to give an MnH]⁺· ion; (c) dehydrogenation; (d) elimination of a 2-carbon C₂H₂ or C₂H₄ fragment; (e) elimination of a C₃H₄ or C₃H₆ fragment as a neutral species when it is bridging two carbon atoms bonded to manganese, as in C₈H₉Mn(CO)₃ and 1,2,3,4,5,h⁵-C₈H₁₁Mn(CO)₃, respectively. Fragmentation of the M – 3CO]⁺· ion in (CH₃)₂NCH₂C₅H₄Mn(CO)₃ presents the following additional features: (a) elimination of C₆H₆ with a nitrogen shift from carbon to manganese; (b) elimination of a neutral dimethylamino fragment to give C₆H₆Mn]⁺·, which then loses neutral C₆H₆, C₆H₅ or Mn fragments and thus is formulated tentatively as (fulvene)Mn]⁺· or C₆H₅MnH]⁺· rather than (benzene)Mn]⁺·.