Mass spectrometry of derivatives of dicyclopentadienyltitanium dichloride I. Behavior in electron impact ionization mass spectrometry

Abstract

Electron impact (EI) mass spectra of ten derivatives of dicyclopentadienyltitanium (IV) dichloride were studied. Fragmentation pathways were constructed and confirmed using daughter-ion, parent-ion and neutral-species loss scan modes of MSIMS.Studies of the electron impact (EI) and chemical ionization (CI) mass spectra of organotitanium compounds have been reported by previous investigators.'. In our work, we studied the derivatives of dicyclopentadienyltitanium (IV) dichloride. These compounds are so reactive that their molecular ions can only be observed using negative-ion CI and not in most other ionization methods such as EI, positive-ion CI (PCI), fast-atom bombardment (FAB), electrospray (ES), atmospheric pressure chemical ionization (APCI) and in particle beam ionization (PBI). In this paper, the compounds were studied using daughter ion, parent ion and neutral-species loss scan modes, so that their EI mass spectrometry fragmentation pathways can be confirmed. The compounds used in this work are given in Table 1. EXPERIMENTALAll samples were synthesized at East China University of Science and Technology and the purity of the samples was determined using IR and NMR spectrometry. Additionally, no impurity peaks were observed in the mass spectra. The EI and CI mass spectra were acquired using a Finnigan TSQ 7000 tandem mass spectrometer equipped with an EI/CI/FAB ion source. The source temperature was 150 "C and electron energy was 70 eV. Ammonia was used as the CI reagent gas at a pressure of 7000 mTorr at the ion source. The parent ion, daughter ion and neutral-species loss scans were acquired at the same source temperature and electron energy. The CID gas used was argon (99.99%) at about 1.0 m Torr pressure. The collision energy was -3OV. RESULTS AND DISCUSSIONThe EI mass spectral data of the compounds listed in Table 1 are presented in Table 2. These mass spectra are regular and not complex. A detailed scheme of the fragmentation pathways of the compounds was established and confirmed using daughter ion, parent ion and neutral-species loss scan techniques (see Scheme 1).* Author for correspondence a RMM = relative molecular masses.No molecular ion was observed in the EI mass spectra. Usually the more abundant ions are b, d and e and the base peak is e. Figure 1 There are three kinds of decomposition mechanisms in the El mass spectra of these compounds. In the first pathway, the molecular ion a is fragmented, losing C1 radical to form ion b. Then ion b fragments, losing another C1 radical to form ion c. Because no molecular ion was observed in any positive-ion mass spectrometry, the [M+NH,]+ ion observed in the PCI/ammonia ionization mode was selected to help confirm this fragmentation route. Thus, the fragmentation path was confirmed by parent-ion scanning of [M -C1]+ (PCUammonia) ions and [M -2C1]+ (EI) ions. Figure 2 shows the parent-ion spectra displayed under CID conditions of the ion at m/z 326 (EI) and