Fischer Carbene Complexes: The Role of Rearrangements in Generating Unexpected Compounds

Over the decades, the outstanding reactivity of Fischer carbene complexes (FCCs) has fascinated those devoted to synthesizing intricate chemical architectures. Among the numerous features of these species, the commonly unexpected rearrangement processes deserve special attention, in which the metal (Cr, Mo, W, and others) plays a crucial role. On the one hand, this review provides a categorized overview of the topic, presenting the most critical information available over the last 25 years. Furthermore, it serves as a guide to understanding the nuances between the reactivity of the metals themselves. The [1,2]-, [1,3]-, and [1,5]-shifts are significant rearrangements intrinsic to FCCs and can be modulated by secondary agents and conditions (thermal, photochemical, etc.). At the same time, this compilation includes a division focusing on cases in which migration occurred within the organic frame but whose procedure was promoted by the metal center. The final section highlights the high potential of these chemical phenomena and opens the pathway to explore their scope, particularly in future synthetic applications.