Structure of the decamethyl titanocene cation,a metallocene with two agostic C-h bonds,and its interaction with fluorocarbons

The tetraphenylborate salt of the decamethyl titanocene cation, Cp*2Ti]BPh4] (1, Cp* = C5Me5), was prepared by reaction of Cp*2TiH with Cp2Fe]BPh4] and by reaction of Cp*2TiMe with PhNMe2H]BPh4]. The crystal structure of 1 shows that the Cp*2Ti cation has a bent metallocene structure with agostic interactions with the metal center of two adjacent methyl groups on one of the Cp* ligands. Compound 1 reacts readily with THF to give the adduct Cp*2Ti(THF)]BPh4] (2). In fluorobenzene, 1 forms the eta1-fluorobenzene adduct Cp*2Ti(eta1-FC6H5)]BPh4] (3), which was structurally characterized. In contrast to the thermal stability of 3, addition of alpha,alpha,alpha-trifluorotoluene to either 1 or 2 results in C-F activation to give Cp*2TiF2 and PhCF2CF2Ph as the main products. This reactivity toward benzylic C-F bonds is also reflected in the reactivity toward the fluorinated borate anions B(C6F5)4]- and {B(3,5-(CF3)2C6H3]4}-: reaction of Cp*2TiMe with their PhNMe2H]+ salts results in a stable complex for the former anion, whereas rapid C-F activation is observed for the latter.