Iridium amides

A resolution of racemic CHIRAPHOS ligand has been achieved using a chiral iridium amide complex (Scheme 8.3). The chiral iridium complex (- -)-l reacts selectively with (S.S -CHIRAPHOS to form the inactive iridium complex 2. The remaining (R,R)-CHIRAPHOS affords the catalytically active chiral rhodium complex 3. The system catalyzes asymmetric hydrogenation to give the (5)-product with 87% ee. The opposite enantiomer (—)-l gives the (R)-product with 89.5% ee, which is almost the same level of enantioselectivity obtained by using optically pure (5,5)-CHlRAPHOS. 

Reaction of 16-Electron Ruthenium and Iridium Amide Complexes with Acidic Alcohols Intramolecular C-H Bond Activation and the Isolation of Cyclometalated Complexes... 

Koike, T. Ikariya, T. Reaction of 16-electron ruthenium and iridium amide complexes with acidic alcohols Intramolecular C-H bond activation and the isolation of cyclometalated complexes. Organometallics 2005, 24, 724-730. 

We also found that iridium hydrido(hydroxo) complexes like [ lrH(diphos-phine) 2( x-OH)2( x-Cl)]Cl (43) and the precursor diphosphine complexes 42 can also catalyze the hydration of nitriles. In the presence of catalyhc amounts of these complexes, heating acetonitrile and benzonitrile with excess water at 120°C gave the corresponding amides [47, 50]. 

The stereochemistry of reduction by homogeneous catalysts is often controlled by functional groups in the reactant. Delivery of hydrogen occurs cis to a polar functional group. This behavior has been found to be particularly characteristic of an iridium-based catalyst that contains cyclooctadiene, pyridine, and tricyclohexylphosphine as ligands, known as the Crabtree catalyst 6 Homogeneous iridium catalysts have been found to be influenced not only by hydroxy groups, but also by amide, ester, and ether substituents.17... 

This lowering of the selectivity may be attributed to competitive binding between the hydroxyl and amide groups to iridium [37]. In entries 6, 7 and 8, the directivity of the hydroxyl group at the bishomoallylic position effectively overrides the effect of the carbamate unit [38]. In the hydrogenation of methylenebi-... 

Other functional groups which have a heteroatom rather than a hydroxyl group capable of directing the hydrogenation include alkoxyl, alkoxycarbonyl, carboxylate, amide, carbamate, and sulfoxide. The alkoxy unit efficiently coordinates to cationic iridium or rhodium complexes, and high diastereoselectivity is induced in the reactions of cyclic substrates (Table 21.3, entries 11-13) [25, 28]. An acetal affords much lower selectivity than the corresponding unsaturated ketone (Table 21.3, entries 14 and 15) [25]. 

The amide group shows a prominent directivity in the hydrogenation of cyclic unsaturated amides by a cationic iridium catalyst, and much higher diastereo-selectivity is realized than in the corresponding ester substrates (Table 21.7). In the case of / ,y-unsaturated bicyclic amide (entry 3), the stereoselectivity surpasses 1000 1 [41]. An increase of the distance between the amide carbonyl and olefmic bond causes little decrease in the selectivity (d, -unsaturated amide, entry 6) compared with the case of the less-basic ester functionality (Table 21.6, entry 5). 

Reactions of amines with alkenes have been reviewed298,299. Alkali metal amides are active homogeneous catalysts for the amination of olefins. Thus diethylamine and ethylene yield triethylamine when heated at 70-90 °C at 6-10 atm in the presence of lithium diethylamide and /V./V./V. /V -tetrarncthylcthylcncdiaminc. Solutions of caesium amide promote the addition of ammonia to ethylene at 100 °C and 110 atm to give mixtures of mono-, di- and triethylamines300. The iridium(I)-catalysed addition of aniline to norbomene affords the anilinonorbomane 274301. Treatment of norbomene with aniline... 

Bis-allylic oxidation of 23 and related cyclohexa-1,4-dienes provides a convenient and general preparation of cyclohexa-2,5-dien-l-ones (Scheme 7). These cross-conjugated die-nones are substrates for a variety of photochemical rearrangement and intramolecular cycloaddition reactions. Amide-directed hydrogenations of dienones 24a and 24b with the homogeneous iridium catalyst afford cyclohexanones 25a and 25b, containing three stereogenic centers on the six-... 

Iridium-Catalyzed Asymmetric Hydrogenation of Olefins with Chiral N,P and C,N Ligands 55 Table 4 Asymmetric hydrogenation of a-substltuted a,(3-unsaturated amides with ligand 24... 

Scheme 21 Iridium catalyzed conversion of an alcohol to a primary amide...

The use of ethylene adduct lb is particularly important when the species added to activate catalyst la is incompatible with one of the reaction components. Iridium-catalyzed monoallylation of ammonia requires high concentrations of ammonia, but these conditions are not compatible with the additive [Ir(COD)Cl]2 because this complex reacts with ammonia [102]. Thus, a reaction between ammonia and ethyl ciimamyl carbonate catalyzed by ethylene adduct lb produces the monoallylation product in higher yield than the same reaction catalyzed by la and [Ir(COD)Cl]2 (Scheme 27). Ammonia reacts with a range of allylic carbonates in the presence of lb to form branched primary allylic amines in good yield and high enantioselectivity (Scheme 28). Quenching these reactions with acyl chlorides or anhydrides leads to a one-pot synthesis of branched allylic amides that are not yet directly accessible by metal-catalyzed allylation of amides. 

The carbonyl intermediate then reacts readily with a primary amine to afford an imine and water. A subsequent addition of the iridium hydride to the C=N double bond of the imine, followed by amide-alkoxide exchange, would then occur to release the product. 

Stripping is easy with dilute acid or water, which deprotonates the amide and releases the metal anion. The process favors metals in high oxidation states [e.g., platinum(IV) or iridium(IV)], so that reduction of any iridium... 

In the commercial flow sheets, these elements are left in the aqueous raffinate after platinum and palladium extraction. Indium can be extracted in the -l-IV oxidation state by amines (see Fig. 11.11), or TBP (see Figs. 11.10 and 11.12). However, although the separation from rhodium is easy, the recovery of iridium may not be quantitative because of the presence of nonextractable iridium halocomplexes in the feed solution. Dhara [37] has proposed coextraction of iridium, platinum, and palladium by a tertiary amine and the selective recovery of the iridium by reduction to Ir(III). Iridium can also be separated from rhodium by substituted amides [S(Ir/ Rh) 5 X 10 ). 

For the hydrogenation of a related cyclopentenyl amide substrate. Brown was able to characterize all steps of the proposed mechanism including the first alkene dihydrides of the missing type using the iridium DIPAMP catalyst [33]... 

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). 

The isomerization of the (Z)-isomer into the ( )-isomer promoted by the iridium complex explains the lack of stereospecificity of the transformation. O-Alkylated oximes and ketoximes do not react and this fact suggests that the presence of both hydrogen and a hydroxyl group is required for the success of the transformation. The authors proposed that the initial displacement of a chloride ion of the iridium complex by the oxime allows the iridium to remove both the oxygen and the hydride from the initial oxime. Swapping places of both substituents produces the amide. 

Weniger gut ist die asymmetrische Induktion (10-13% de) mit analogen chiralen Iridium-Katalysatoren, obwohl hier sogar zur Unterstutzung ein chirales Alkensaure-amid ein-gesetzt wurde7. 

The Ir(III) metal centres in the products, which are bound to a terminal hydride and a bridging —NH2 group, represented the first X-ray stnictural authentication of a transition metal species with both amide and hydride bound to a metal centre. The reactivity of the complexes is low, however, and appears to be dominated by the stability of the lr(p-NH2)2lr bridging unit. More recent work has shown that olefin-iridium(l) complexes, such as the propene species [ HC(CH2CH2PBu 2)2 Ir(CH2CHMe)], react diiectly with ammonia at room temperature as shown in Equation (6.12)." ... 

Di(carbene)gold(I) salts, oxidation, 2, 293—294 Dicarbido clusters, with decarutheniums, 6, 1036 Dicarbollide amides, with tantalum, 5, 184 Dicarbollide thorium complexes, synthesis and characterization, 4, 224—225 Dicarbollyl ligands, in nickel complexes, 8, 185 Dicarbonyl complexes arylation with lead triacetates diastereoselectivity, 9, 389 enantioselectivity, 9, 391 mechanisms, 9, 387 reaction examples, 9, 382 indium-mediated allylation, 9, 675 with iridium, 7, 287 reductive cyclization, 10, 529 in Ru and Os half-sandwiches, 6, 508 with Zr—Hf(II), 4, 700... 

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