Formation of C–C bond is one of the most remarkable transformations in organic chemistry, and it has received special attention since the second half of the 20th century. By the late 1970s, Pd-catalyzed cross-coupling reactions emerged as a powerful tool for the construction of C–C bonds, providing new ways to build molecules. Although these methodologies supposed a significant breakthrough in organic chemistry, they have some limitations such as the instability of some organometallic nucleophiles or the formation of undesired waste due to the use of stoichiometric amounts of organometallic nucleophiles. Because of that, during the last decade, novel catalytic bond-forming reactions have been explored in an attempt to overcome these limitations. Among them, the development of new methodologies based on first-row transition metals and the synergistic cooperation between two metal centers has received special attention. Despite the inherit utility and benefits exhibited by these approaches, important fundamental questions concerning the mechanisms of these transformations or the exact nature of the reactive species still remain unsolved. The presentation will show our mechanistic investigations in an effort to provide answers to some of these questions.