All three research projects fulfilled in the current Thesis deal with new reactions involving activation and cleavage of highly inert C-I, C-Br, C-Cl, and C-F bonds.  Chapter 1 describes a new chemical transformation, Pd-catalyzed synthesis of aroyl azides from iodoarenes, CO, and NaN₃.  This catalytic process exhibits high efficiency (0.2% Pd) and excellent functional group tolerance.  A detailed mechanistic study of the azidocarbonylation reaction has revealed two different reaction pathways operating in the presence of CO in excess and under CO-deficient conditions.  Organometallic intermediates involved in the catalytic cycle have been isolated and fully characterized, including by X-ray diffraction.  Chapter 2 reports a mechanistic study of the novel Ph-X (X = I, Br, Cl) activation with Ru(II) hydrido complexes under exceedingly mild conditions.  Striking zeroth-order kinetics observed for the reaction of [(Ph₃P)₄Ru(H)₂] with PhX (X = I, Br) originates from hidden autocatalysis that has been recognized and fully proven.  Chapter 3 deals with C-F activation of highly inert fluoroform (CHF₃), an industrially side-produced potent greenhouse gas, with alkali metal hydroxides and alkoxides.  The reaction of MOR with CHF₃ has been shown to furnish the corresponding orthoformates, exotic HC(OBu-t)₃ included, in good to excellent yield.  Results of the Thesis contribute to new methodology development, basic knowledge of reaction mechanisms, and potential ecological solutions.