Mass spectra of alkylferrocenes and biferrocenyls

Abstract

AbstractMass spectra of alkylferrocenes and biferrocenyls have molecular ion peaks which are also base peaks. The predominant fragment ions are formed by beta‐cleavage of the alkyl group. Gamma‐and alpha‐cleavages are the only other significant modes of alkyl side‐chain fragmentation. The cleavage of the alkyl group is often accompanied or followed by the cleavage of either one or both of the cyclopentadienyl‐iron bonds. Weak m/e 121 ([C5H5]+) mass peaks are found in the spectra of 1,1′‐dialkyl‐ and 1,1′‐disilyl‐ferrocenes. Therefore, the m/e 121 peak may not be used as a sensitive criterion to determine the presence of unsubstituted cyclopentadienyl rings. The relative intensity of the peak may, however, serve as an indicator.Expansion of the cyclopentadienyl ring to six‐ and seven‐carbon rings in the fragmentation of alkylferrocenes, diethylbiferrocenyl and deuterated ethylferrocenes is indicated. The spectra of benzylferrocene and benzylferrocene‐alpha‐d2 do not show a beta‐cleavage but suggest a pentalene ring formation. Methyl and phenyl groups in the beta‐position of substituted ferrocenes were found to migrate to the iron atom.