Carbene Complexes of Nonmetals

Abstract

Electrophilic carbenes accept a variety of n‐ and π‐donors. The products range from persistent ylides to matrix‐isolated xenon complexes. Ylides can be viewed as carbene complexes if they regenerate carbenes thermally or undergo concerted methylene transfer reactions. According to these definitions, the present review focuses on oxonium and iodonium ylides. Transient π‐complexes appear to be involved in addition reactions of carbenes with arenes (but not with alkenes). Nucleophilic carbenes form adducts with Lewis acids which are, for the most part, stable and have been well characterized structurally. Only recently attention has been directed to reversible systems. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Iodonium ylides in organic synthesis

“…[14][15][16] The product composition in the rhodium(II)-catalyzed reactions of iodonium ylides was found to be identical to that of the corresponding diazo compounds, which confirms that mechanisms of both processes are similar and involve metallocarbenes as key intermediates. Rh(II)-or Cu(II)-catalyzed generation/rearrangement of onium ylides of allyl and benzyl ethers via iodonium ylides; 82 and Rh(II)-or Cu(II)-catalyzed stereoselective cycloaddition of disulfonyl iodonium ylides with alkenes leading to 1,2,3-trisubstituted benzocyclopentenes 83 or functionalized indanes.…”

“…A detailed discussion of the reaction mechanisms and synthetic applications of iodonium ylides as carbene precursors can be found in the earlier reviews. [14][15][16][17][18] Bis(methoxycarbonyl)(phenyliodinio)methanide 4, the most common iodonium ylide derived from malonate methyl ester, has found synthetic applications in the C-H insertion reactions, [57][58][59][60][61] and in the cyclopropanation of alkenes, 22,28,[62][63][64][65][66] including enantioselective cyclopropanations in the presence of chiral rhodium complexes. 15,67,68 Representative examples of these reactions are shown in Scheme 12 and include the BF 3 -catalyzed bis(carbonyl)alkylation of 2-alkylthiophenes 43, 58 and the optimized procedure for rhodiumcatalyzed cyclopropanation of styrene 44.…”

“…The chemistry of aryliodonium ylides has been discussed in several older reviews, which mainly summarized the use of ylides as precursors for generation of singlet carbenes or carbenoid species. [14][15][16][17][18] In the present review, the synthesis and structural studies of iodonium ylides are discussed, and recent developments in their synthetic applications are summarized. The literature coverage is through Spring 2016.…”

Imidazol(in)ium‐2‐carboxylates as N‐Heterocyclic Carbene Precursors for the Synthesis of Second Generation Ruthenium Metathesis Catalysts

“…Indeed, NHCs form stable adducts with a wide range of main group elements [12] and non-metal compounds. [13] So far, the formation of four different types of adducts has been identified to be thermoreversible. Thus, the chloroform and pentafluorobenzene adducts of 1,3-dimes-A C H T U N G T R E N N U N G itylimidazolidin-2-ylidene (nicknamed SIMes) are stable at room temperature but release the corresponding NHC when heated.…”

Applications of iodonium salts and iodonium ylides as precursors for nucleophilic fluorination in Positron Emission Tomography

“…The chemistry of aryliodonium ylides has been summarized in several reviews mainly devoted to their use as precursors for generation of singlet carbene or carbenoid species. [77][78][79][80] …”