This thesis reports investigations on the electrospray ionisation mass spectrometric (ESI-MS) behaviour of some metallocene complexes of titanium and molybdenum. The ESI-MS behaviour of titanocene dichloride (Cp₂TiCl₂) compound, which is has shown of interest as an anticancer agent was investigated. Cp₂TiCl₂ was dissolved in various solvents and spectra were recorded at various capillary exit voltages from 60 V to 250 V. Bis(ethylcyclopentadienyl) dichloridotitanium(IV) was also studied via ESI-MS. Results indicated clearly some main species like [Cp₂TiH]⁺, [Cp₂Ti(OCH₃)]⁺ and [Cp₂Ti(OCH₃)₂+H]⁺ were observed. When the capillary exit voltage was greater than 150 V species containing two Ti centres like [Cp₄Ti₂(OCH₃)₂Cl]⁺, [Cp₄Ti₂(OCH₃)₃Cl+H]⁺ and [(Cp₂Ti(OCH₃)₂+H⁺)₂+Cl]⁻ disappeared and titanocene(III) species [Cp₂Ti(CH₃OH)]⁺ was observed which indicated reduction of titanium(IV) during ESI-MS analysis. Larger ions which contain three or more Ti centres were not observed. The main focus of this thesis was to investigate the chemistry and characterisation of the organometallic compound bis(cyclopentadienyl) thiosalicylatotitanium(IV) (Cp₂Ti(tsal) tsal = SC₆H₄CO₂). A further experiment was done to run the spectrum of a mixed solution of Cp₂TiCl₂ and Cp₂Ti(tsal) in CH₃OH to investigate the possibility of the tsal ligand bridging two Cp₂Ti centres. Characterisation of Cp₂Ti(tsal) using ESI mass spectrometry in the presence of added alkali metal salts and the reactivity of Cp₂Ti(tsal) towards soft electrophile was also studied. At the same time, a new complex bis(ethylcyclopentadienyl) thiosalicylatotitanium(IV) ((EtCp)₂Ti(tsal)) was synthesised and studied by ESI-MS. Comparison of the ESI-MS spectra of Cp₂Ti(tsal) with those of (EtCp)₂Ti(tsal) was used to confirm the identity of some unknown species. This new complex was characterised by elemental analysis, melting point, nuclear magnetic resonance (NMR) and infra-red (IR) spectroscopy. Finally the molybdocene dichloride (Cp₂MoCl₂) compound was studied by ESI-MS. The closely related compound bis(cyclopentadienyl) thiosalicylatomolybdenum(IV) (Cp₂Mo(tsal)) was synthesised and characterised by ESI-MS, melting point, NMR and IR spectroscopy. Less species can be observed in the Mo system than in the Ti system. Most species in the Mo system contained a Cl ligand.