Carbenes substitution

A recent study by Frenking [84] investigated in great detail the influence of the carbene substitutents X and R at a pentacarbonyl-chromium Fischer-type complex. The electronic characteristics of these substituents control the reac-... 

Perhaps most dramatically of all, for the first time, bis(carbene)-substituted iridium complexes, such as [Ir(cod)(NHC)2] (NHC = 1,3-dimethyl- or 1,3-dicyclohexylimidazolin-2-ylidene] were successfully used by Herrmann and coworkers as C—H-activation catalysts in the synthesis of arylboronic acids starting from pinacolborane and arene derivatives [46]. 

Carbenes -substituted with heteroatoms other than halogen... 

In the presence of an imidazole-derived carbene, substituted cinnamaldehydes conjugatively add to tropone leading to the cyclohepta[6]pyranones 22. The overall process corresponds to an [8+3] annulation of tropone <06JOC8964>. 

Among carbenes substituted with another electron-withdrawing group, bis(trifluoromethyl)carbene seems to be the most reactive (Table 15). " ... 

The problem of ambiphilic carbenes has also been considered a carbene. substituted both by an electron donating and an electron-attracting substituents, such... 

Among carbenes substituted with another electron-withdrawing group, bis(trifluoromethyl)carbene... 

A large number of cyclopropanes geminally substituted with two electron-withdrawing groups have been synthesized by cyclopropanation of olefins with carbenes substituted with two electron-withdrawing groups (equation 36) Spiro-activated cyclopropanes... 

The singlet form of carbenes substituted with a carbonyl group is much lower in energy than the triplet, so the photolysis of a-diazocarbonyl compounds gives singlet carbenes. The photo-Wolff rearrangement (Chapter 2) of a-diazoketones occurs upon photolysis of these compounds. 

Certain alkyne and carbene substitution patterns divert the reaction toward predominant indene formation. For example, ynamines and ynediamines both react with chromium arylalkoxycarbenes to give isolable vinyl carbenes, which proceed on to indenes thermally [21 a, b]. Chromium aryla/nmocarbenes also lead to good to excellent yields of indanones after hydrolysis of the enamine [Eq. (19)] [45]. In this latter case, the increased electron-donating... 

Formation of cluster anions on surfaces or in solution involves nucleophilic or electrophilic attack of water, hydroxyl groups, or alcohols on coordinated carbonyl groups this behavior is relevant both to the WGSR reaction and to the formation of carbene-substituted complexes and related derivatives. Examples in organic solvents are ... 

Carbon-13 NMR parameters for all metal carbonyl complexes discussed in this section appear in Table XL. Additional carbonyl data for carbene substituted metal carbonyl complexes may be found in Tables XXXVI and XXXVII. Notably absent from this section is a discussion of polynuclear metal carbonyl complexes. These studies are considered in the section of fiuxional complexes. It is sufScient to note at this point that bridging carbonyl ligands always appear at lower fields than terminal carbonyl ligands. 

Sol 11. Carbenes substituted with electron-withdrawing carbonyl groups are more powerful electrophiles than simple carbenes and will even add to the double bonds of benzene. The product is not stable but immediately undergoes electrocyclic ring opening. 

Lane DR, Beavers CM, Olmstead MM, Schore NE. Steric and Electronic Effects of Carbene Substitution in Grubbs First-Generation Catalysts. OrganometaUks. 2009 28(23) 6789-6797. 

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