Iridium complexes rearrangements

The same activity is presented by an iridium complex [Ir(Cp )Cl2]2 that catalyses the Beckmann rearrangement of aromatic, aliphatic and heteroaromatic aldoximes 276 into the corresponding primary amide 277 in good to excellent yields (78-97%) (equation 85). 

In accessing chiral allyl vinyl ethers for Claisen rearrangement reactions, Nelson et al. employed the iridium-mediated isomerization strategy. Thus, the requisite enantioenriched diallyl ether substrate 28 was synthesized via a highly enantioselective diethylzinc-aldehyde addition protocol10 (Scheme 1.1k). The enantioselective addition of Et2Zn to cinnamaldehyde catalyzed by (—)-3-exo-morpholinoisobomeol (MIB 26)11 provided an intermediate zinc alkoxide (27). Treatment of 27 with acetic acid followed by 0-allylation in the presence of palladium acetate delivered the 28 in 73% yield and 93% ee. Isomerization of 28 with a catalytic amount of the iridium complex afforded the allyl vinyl ether... 

Only when this tricarbonyl species is formed does the rearrangement to the acetyl-iridium complex occur. The observation that the neutral tricarbonyl complex rearranges to form an acetyl species much more readily than the anionic dicarbonyl species undoubtedly can be related to the relative strengths of the individual Ir-CO bonds in the two complexes. Similarly, the marked contrast to this type of reactivity with that of the rhodium system, where the analogous CH3Rh(CO)2I3 has never been detected because of... 

Tilley reported silene-silylene rearrangement in a cationic iridium complex (Eq. 13) [13b]. 

Hydrogen addition to Ir(CO)(dppe)(X) leads first to the isomer with X trans to one phosphorus of dppe in a reversible reaction. This kinetic isomer then rearranges to the thermodynamic isomer that has CO trans to a phosphorus atom of dppe. For X = H or PPh3, no rearrangement of the initially formed product is observed . Addition of H2 to an iridium complex containing the optieally active diphosphine chiraphos [bis(S),(S)-2,3-(diphenylphosphino)butane] was described - . The H2 addition to analogues of... 

Rearrangement. Transformation of 2-aIkenols to 3-amino-l-aUcenes can be performed via decarboxylative rearrangement of the derived carbamates, the iridium complex of 2B possesses activity for endowing chirality to the amines. When crotyl (J-ketoalkanoate and homologues are exposed to the iridium complex of 2A in the presence of DBU, rearrangement and decarboxylation occur, forming optically active l-aIken-5-ones. ... 

A Cr(VI) sulfoxide complex has been postulated after interaction of [CrOjtClj] with MejSO (385), but the complex was uncharacterized as it was excessively unstable. It was observed that hydrolysis of the product led to the formation of dimethyl sulfone. The action of hydrogen peroxide on mesityl ferrocencyl sulfide in basic media yields both mesityl ferrocenyl sulfoxide (21%) and the corresponding sulfone (62%) via a reaction similar to the Smiles rearrangement (165). Catalytic air oxidation of sulfoxides by rhodium and iridium complexes has been observed. Rhodium(III) and iridium(III) chlorides are catalyst percursors for this reaction, but ruthenium(III), osmium(III), and palladium(II) chlorides are not (273). The metal complex and sulfoxide are dissolved in hot propan-2-ol/water (9 1) and the solution purged with air to achieve oxidation. The metal is recovered as a noncrystalline, but still catalytically active, material after reaction (272). The most active precursor was [IrHClj(S-Me2SO)3], and it was observed that alkyl sulfoxides oxidize more readily than aryl sulfoxides, while thioethers are not oxidized as complex formation occurs. 

The formation of ci5-dihydride in iridium complexes related to rhodium asymmetric hydrogenation catalysts has been observed at low temperature see equation (12). They rearrange to a different dihydride at —45 C and react at —25 °C... 

Iridium The intermolecular hydroamination of unactivated C=C bonds in ct-olefins (RCH=CH2) and bicycloalkenes (norbornene and norbornadiene) with arylamides (ArCONH2) and sulfonamides has been attained upon catalysis by chiral iridium complexes (PP)IrHCl(NHCOAr)(NH2COAr) [PP = chiral bidentate diphosphine]. Mechanistic studies identified the product of N-H bond oxidative addition and coordination of the amide as the resting state of the catalyst. Rapid, reversible dissociation of the amide precedes reaction with the alkene, but an intramolecular, kinetically significant rearrangement of the species occurs before the reaction with alkene. ... 

The insertion reactivity of the electrophilic iridium methylene species 57 was noted above. A cationic iridium methylene complex is also the likely intermediate in the thermal rearrangement of Ir(=CH2)I(CO)(PPh3)2 to the ortho-metallated ylide complex 75 ([Pg.167]

The differences between the iridium and rhodium systems were interpreted by considering that Int 1 may open an oxygenation path via intramolecular rearrangement. In this case, the scission of a M-0 bond between the semi-quinone and metal center would be followed by intra-diol insertion of an oxygen and ultimately by the formation of muconic acid and water. The results indicate partial preference of the rhodium complex toward the oxygenation path. 

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