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Guilherme Mazui

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What is the Difference Between Fischer and Schrock Carbene?

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The main difference between Fischer and Schrock carbenes lies in their electronic structures, reactivities, and the types of metal centers they typically feature.

Fischer carbenes (named after Ernst Otto Fischer) have the following characteristics:

  • Feature strong π-acceptors at the metal
  • Carbene carbon atom is electrophilic
  • Typically contain low oxidation state metal centers, such as middle and late transition metals like iron, molybdenum, and cobalt
  • Can undergo aldol-like reactions and have acidic hydrogen atoms attached to the carbon atom α to the carbene carbon atom

Schrock carbenes (named after Richard R. Schrock) have the following characteristics:

  • Characterized by more nucleophilic carbene carbon centers
  • Typically feature higher valent metals, such as early transition metals like titanium
  • Formed with the metal centers having more electron-rich ligands

Due to their different electronic structures, the reactivities of Fischer and Schrock carbene complexes differ significantly. Fischer type carbene complexes undergo nucleophilic attack at the carbene carbon center, while Schrock type carbene complexes undergo electrophilic attack at the carbene carbon center.

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  • What is the Difference Between Fischer and Schrock Carbene?
  • Comparative Table: Fischer vs Schrock Carbene

    • Comparative Table: Fischer vs Schrock Carbene

    Here is a table comparing the differences between Fischer and Schrock carbenes:

    Property Fischer Carbene Schrock Carbene
    Carbon Center Weak back bonding metal center, usually a low oxidation state Strong back bonding carbon center
    Carbon Ligands Contains a π-chelating ligand Contains a π-accepting ligand
    Synthesis Developed in 1964, carbon is electrophilic, and common method is nucleophilic attack at a carbonyl ligand Nucleophilic attack at a carbonyl ligand, α-abstraction in Schrock carbenes synthesis, induced by steric bulk
    Stability Can be enhanced by highly electronegative heteroatoms, which participate in π-back bonding with d orbitals on the carbon Less stable, alpha abstraction is typically present, and it is not stabilized by the participation of heteroatoms in π-back bonding
    Saturation Saturated complexes Unsaturated complexes

    Fischer carbenes have a weak back bonding metal center and are classified as saturated complexes, while Schrock carbenes have a strong back bonding carbon center and are classified as unsaturated complexes. The carbon in Fischer carbenes is electrophilic, while Schrock carbene carbon is nucleophilic.

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    Guilherme Mazui

    Guilherme Mazui is graduated in journalism from the Federal University of Minas Gerais (UFMG) and a master's degree in Communication from the University of São Paulo (USP). In addition, he has experience in advertising writing and has worked as a content editor in several companies.