We have applied a density-functional derived tight-binding method (DF-TBMD) to the study of the energetics and the dynamics of boron defects in silicon. This study is motivated by a number of interstitial-driven phenomena observed in experiments, as the transient enhanced diffusion of B atoms in implanted silicon samples together with the formation of immobile B precipitates. We discuss first the DF-TBMD results for equilibrium structures and formation energies of different defect configurations containing a single boron atom and a silicon self-interstitial. Moreover, DF-TBMD molecular dynamics simulations at finite temperature allow us to investigate boron diffusivity in a temperature range between 900 and 1500 K. We provide for the first time a dynamical picture of B diffusion in silicon characterized by a migration energy of 0.7 eV.