Catalytic Transmetalation from Group 6 Fischer Carbene Complexes:  An Emerging Powerful Tool in Organic Synthesis

Abstract

The chemistry of metal carbene complexes has experienced an enormous development in the past decades. Despite this fact, the use of transition metals as catalysts in reactions involving group 6 Fischer carbene complexes was virtually neglected. Here, we describe how the reactivity of these compounds can be enhanced or modified in the presence of catalytic amounts of a transition metal, leading to new forms of reactivity and others offering clear advantages in terms of efficiency over the uncatalyzed reactions. The key step for these reactions is the transmetalation from the stoichiometric metal carbene reagent to the catalyst. This process generates a new metal-carbene complex that leads to enhanced reactivity of new reaction modes. Two examples of Fischer carbene complexes obtained by transmetalation to Pd and Cu have been isolated during the last 2 years, showing the flexibility if the mechanistic hypothesis for these reactions. The work presented in this Account shows how an area, which was practically unexplored 5 years ago, has emerged as a new and powerful field of research.

Carbene ligands in diiron complexes

“…Since the first tungsten(0) carbene complex reported by Fischer and Maasbö l in [1], transition metal carbene complexes have experienced a rapid and enormous development which has been paralleled by applications in organic synthesis [2] and catalysis [3]. Both heteroatom stabilized carbenes (Fischer) and electrophilic (Schrock) [4] carbenes are considered among the most versatile organometallic reagents.…”

Recent advances in the field of multicarbene and multimetal carbene complexes of the Fischer-type

“…4.) [34]. This bis(ethoxycarbene) intermediate of palladium (6) could be stabilized by incorporating the carbene ligands into fivemembered N,C-chelate rings [33,36]. Sierra and co-workers used palladium catalysts for intramolecular carbene-carbene coupling reactions of biscarbene complexes of Cr and W (Scheme 1, 7) to achieve a ring closure reaction with different outcomes for the final products depending on the precursors being of the o-dioxobenzene or o-diaminobenzene class of compounds [37].…”

Advances in the synthesis and reactivity of 2-pyranylidene carbene complexes

“…Fischer-type carbene complexes are among the most important organometallic compounds, and these have experienced a considerable surge in recent times because of their widespread application in synthetic organic chemistry since the first carbene complex was reported by Fischer and coworkers in 1964 [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. During the course of the development of Fischer-type carbene complexes, unsaturated Fischer carbene complexes, in which unsaturated substituents are attached to the carbene carbon center, occupy an important status owing to their good reactivity in Michael-type reactions, cycloaddition reactions, transmetalation reactions.…”

“…During the course of the development of Fischer-type carbene complexes, unsaturated Fischer carbene complexes, in which unsaturated substituents are attached to the carbene carbon center, occupy an important status owing to their good reactivity in Michael-type reactions, cycloaddition reactions, transmetalation reactions. The strong electron-withdrawing property of the pentacarbonyl metal moiety and the electron-deficient property of the β-position carbon resulting from electron-transfer from the carbene center play a cooperative effect on the versatile reactivity of unsaturated Fischer carbene complexes [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. 2-Pyranylidene metal carbene complexes bearing a pyran ring carbene ligand are a special kind of unsaturated Fischer carbene complex, that has received much less attention probably because of their limitation of the synthetic methodology.…”