A density functional theory computational chemistry study has revealed a fundamental structural difference between [Ti(Cp)3]+ and its congeners [Zr(Cp)3]+ and [Hf(Cp)3]+/(Cp=cyclopentadienyl). Whereas the latter two are found to contain three uniformely η5-coordinated Cp ligands (3η5-structural type), [Ti(Cp)3]+ is shown to prefer a 2η5η2 structure. [Ti(Cp)3]+[B(C6F5)3(Me)]− (10⋅[B(C6F5)3(Me)]−) was experimentally generated by treatment of [Ti(Cp)3(Me)] (7a) with B(C6F5)3 (Scheme 3). Low-temperature 1H-NMR spectroscopy in CDFCl2 (143 K, 600 MHz; Fig. 8) showed a splitting of the Cp resonance into five lines in a 2 : 5 : 2 : 5 : 1 ratio which would be in accord with the theoretically predicted 2η5η2-type structure of [Ti(Cp)3]+. The precursor [Ti(Cp)3(Me)] (7a) exhibits two 1H-NMR Cp resonances in a 10 : 5 ratio in CD2Cl2 at 223 K. Treatment of [HfCl(Cp)2(Me)] (6c) with sodium cyclopentadienide gave [Hf(Cp)3(Me)] (7c) (Scheme 1). Its reaction with B(C6F5)3 furnished the salt [Hf(Cp)3]+[B(C6F5)3(Me)]− (8⋅[B(C6F5)3(Me)]−), which reacted with tert-butyl isocyanide to give the cationic complex [Hf(Cp)3(C=N−CMe3)]+ (9a; with counterion [B(C6F5)3(Me)]− (Scheme 2). Complex cation 9a was characterized by X-ray diffraction (Fig. 7). Its Hf(Cp3) moiety is of the 3η5-type. The structure is distorted trigonal-pyramidal with an average D−Hf−D angle of 118.8° and an average D−Hf−C(1) angle of 96.5° (D denotes the centroids of the Cp rings; Table 6). Cation 9a is a typical d0-isocyanide complex exhibiting structural parameters of the C≡N−CMe3 group (d(C(1)−N(2))=1.146 (5) Å; IR: v˜(C≡N) 2211 cm−1) very similar to free uncomplexed isonitrile. Analogous treatment of 8 with carbon monoxide yielded the carbonyl (d0-group-4-metal) complex [Hf(Cp)3(CO)]+ (9b; with counterion [B(C6F5)3(Me)]−) (Scheme 2) that was also characterized by X-ray crystal-structure analysis (Fig. 6). Complex 9b is also of the 3η5-structural type, similar to the peviously described cationic complex [Zr(Cp)3(CO)]+, and exhibits properties of the CO ligand (d(C−O)=1.11 (2) Å; IR: v˜(C≡O) 2137 cm−1) very similar to the free carbon monoxide molecule.