[RUCl2(PPh3)(3)] reacts with thallium(l) fluoride to give either [Tl(mu-F)(3)Ru(PPh3)(3)] (1) or [Tl(mu(3)-F)(mu(2)-Cl)(2)Ru-2(mu(2)-Cl)(mu(2)-F)(PPh3)(4)] (2) depending on the excess of TIF used. Both 1 and 2 were fully characterized, including X-ray structure determinations. Complex 1 reacts with dihydrogen to form the known ruthenium hydride complex [Ru(H)(2)(H-2)(PPh3)(3)] upon hydrogenolysis of the Ru-F bond. The reaction of 1 with activated alkyl bromides (R-Br) gives the corresponding alkyl fluorides and the trinuclear complex [Tl(mu(3)-F)(mu(2)-F)(mu(2)-X)Ru-2(mu(2)-Br)(rho(2)-F)(PPh3)(4)] (X = Br, F) (3), whose structure closely resembles that of 2. However, 1 is not active as catalyst for the nucleophilic fluorination of R-Br in the presence of thallium fluoride. The effect of the bridging coordination mode of fluoride on the Ru-F bond is discussed in terms of the HSAB principle, which suggests a more general model for predicting the stability of d(6) and d(8) complexes containing hard ligands (such as fluoro, oxo, and amido).