Carbenes and Nitrenes

This Chapter Contains Sections titled: Reviews Generation, Structure, and Reactivity Carbenes in Coordination Chemistry Addition–Fragmentations Free Carbenes or Main Group Carbenoids Reactions Transition-Metal-Assisted Reactions Insertion–Abstraction Free Carbenes or Carbenoids Reactions Transition-Metal-Assisted Reactions Rearrangements Free Carbenes or Carbenoids Reactions Nucleophilic Carbenes–Carbenes as Organocatalysts Transformations Mediated by Breslow-Type Intermediates Transformations Non-Mediated by Breslow-Type Intermediates Nitrenes Free Nitrenes – Generation and Reactivity Transition-Metal-Assisted Reactions Heavy-Atom Carbene Analogues References Carbenes, especially N-heterocyclic carbenes (NHC), have proved to be excellent 'ligands' of main group atoms, including carbon, and allowed the generation of carbodicarbenes, these structures being mesomeric resonance structures of cumulenes. This chapter reviews the use of water in a range of metal-catalysed transformations involving NHC. It covers both homogeneous and heterogeneous approaches and describes transformation involving NHC-metal complexes of palladium, ruthenium, gold, rhodium, copper, iridium, silver, platinum, and nickel as well as transformation featuring NHCs as organocatalysts. Transition metal carbenoids are widely examined for their high potential to act as cyclopropanating agents. Cyclopropenes have been demonstrated to be powerful zinc vinyl carbenoid precursors, thus furnishing vinylcyclopropane derivatives via their addition to alkenes. The O-NHAc moiety of the substrate plays the role of both directing group for the intermolecular C-H insertion step and internal oxidant. The chapter investigates the rearrangement of diverse γ-trimethylsilyl-substituted carbenes by means of experimental and computational methods.