Fischer carbene complexes, and

Cr(CO)3-coordinated hydroquinone from vinylic alkoxy pentacarbonyl chromium carbene (Fischer carbene) complex and alkynes. 

Table 8 Acidities of Fischer carbene complexes and intrinsic rate constants for their deprotonation by secondary alicyclic amines, primary aliphatic amines and hydroxide ion in 50% MeCN-50% water (v/v) at 25°C... 

Numerous authors189-191 have compared the reactions of Fischer carbene complexes with nucleophiles to the corresponding reactions of carboxylic esters.183,185-187 Our view is that there is much more resemblance between the reactions of Fischer carbene complexes and SNV reaction than between the reactions of Fischer carbene complexes and reactions with esters because in the latter reactions there are no strong resonance effects. 

A very rapid growth of novel and synthetically usefiil reactions of Fischer-type carbene complexes see Fischer-type Carbene Complexes) has occurred over the last decade. Reactions leading to cychc and polycyclic compounds of high complexity and reactions wherein chirahty has been transferred from the starting material to the product are of particular importance. A number of recent reviews on the chemistry of Fischer carbene complexes and their application in organic synthesis are avaUable. ... 

Merlic, C. A., Aldrich, C. C., Albaneze-Walker, J., Saghatelian, A., Mammen, J. Total Synthesis of the Calphostins Application of Fischer Carbene Complexes and Thermodynamic Control of Atropisomers. J. Org. Chem. 2001, 66, 1297-1309. 

Ab initio MO calculations have been reported on complexes 15 and 16 the former is a good example of a Fischer carbene complex and the latter is a Schrock-type.9... 

The Chemistry of Mid- to Late Transition Metal Fischer Carbene Complexes and Alkylidenes... 

Functionalized benzo[b]furan-based heterocycles were made from Fischer carbene complexes and heterocycle-bridged enynes in good to acceptable yields <05TL2211>. 

Alkoxy-3-pyrrolines. Fischer carbene complexes and aldimines undergo cycloaddition in the presence of GaCl,. The major products have a tran.s-2,5-disubstitution pattern (trans cis ratio in the 8 2 range). 

Vinylidene complexes are electrophilic at the a-carbon. Therefore, they display reactivity more similar to that of Fischer-type carbene complexes than to that of Schrock-type carbene complexes. This trend fits with lire greater stability of the singlet spin state (and therefore higher HOMO-LUMO gap) of the free carbene in most Fischer carbene complexes and in vinylidenes. This trend also fits with the low oxidation state of the metal in most Fischer carbene complexes and vinylidene complexes. At the same time, some reactivity of vinylidine complexes is unique to those containing the cumulated unsaturation of a vinylidene unit. For example, the 3-carbon of a vinylidene ligand is nucleophilic and basic. 

The corresponding [3 + 2 + 2]- and [2 + 2 + 2 + l]-cyclization reactions between these complexes and alkynes are very efficient in the presence of Ni(0). Transmetallation reactions between chromium Fischer carbene complexes and Ni(cod)2 with formation of nickel carbene intermediates is presumed to be responsible for this transformation. The metal-free cycloadducts are easily obtained by ligand exchange reactions at low GO pressures. A [3-h2]-cyclization reaction of a chromium Fischer carbene complex and allene building blocks was accomplished, using... 

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