Hydroamination iridium catalyst

This chemistry was extended to a number of bicyclic alkenes and dienes utilizing various chelating axially chiral bisphosphine iridium catalysts (Scheme 11.5) [29]. Further synthetic transformations of the chiral hydroamination product 13 provide access to functionally substituted chiral cyclopentylamines with multiple stereocenters, such as 14 and IS. It should be noted that alkylamines, such as octylamine or N methyl aniline, and sterically encumbered aniline derivatives, such as 0 toluidine or o anisidine did not undergo hydroamination reactions under these conditions. 

The first transition metal-catalyzed hydroamination of an olefin was reported in 1971 by Coulson who used rhodium(I), rhodium(III) or iridium(III) catalysts (Eq. 4.8) [105,106]. 

Iridium(ni) hydrides, such as (98), proved to be air-stable active catalysts for intramolecular hydroalkoxylation and hydroamination of internal alkynes with proximate nucleophiles (e.g. 96). The cyclization follows the 6-endo-dig pathway with high preference (when regioselectivity is an issue).125... 

Earher mechanistic studies by Milstein on a achiral Ir catalyst system indicated that the iridium catalyzed norbornene hydroamination involves amine activation as a key step in the catalytic cycle [27] rather than alkene activation, which is observed for most other late transition metal catalyzed hydroamination reactions [28]. Thus, the iridium catalyzed hydroamination of norbornene with aniline is initiated by an oxidative addition of aniline to the metal center, followed by insertion of the strained olefin into the iridium amido bond (Scheme 11.4). Subsequent reductive elimina tion completes the catalytic cycle and gives the hydroamination product 11. Unfor tunately, this catalyst system seems to be limited to highly strained olefins. 

Ebrahimi, D., Kennedy, D. F., Messerle, B. A. Hibbert, D. B. (2008). High throughput screening arrays of rhodium and iridium complexes as catalysts for intramolecular hydroamination using parallel factor analysis. Analyst, Vol. 133,... 

The intermolecialar hydroamination has also received some attention and studies in this area have focussed on the use of iridium and nickel catalysts. Enan-tioselectivities for the intermolecular process are also generally moderate with ees observed between 60 and 70%. The highest enantioselectivities for this reaction have been obtained during the hydroamination of norbornene (2.145) with aniline in the presence of the iridium complex (2.184) and the fluoride ion source... 

In other cases, the properties of fluoride ligands have been exploited to generate more active catalysts than are obtained in the absence of added fluoride or with other halogen ligands. As described in Chapter 16, added fluoride accelerates the rate of the iridium-catalyzed hydroamination of norbomene with aniline. The origin of this effect has not been revealed. 

As discussed in Chapter 9, the insertion of olefins and alk)nes into metal-amido complexes is limited to a few examples. Such insertion reactions are proposed to occur as part of the mechanism of the hydroamination of norbomene catalyzed by an iridium(I) complex and as part of the hydroamination of alkenes and alkynes catalyzed by lanthanide and actinide metal complexes. This reaction was clearly shown to occur with the iridium(I) amido complex formed by oxidative addition of aniline, and this insertion process is presented in Chapter 9. The mechanism of the most active Ir(I) catalyst system for this process involving added fluoride is imknown. 

P,N-Phosphine imine complexes of iridium (25) have also proved to be successful in intramolecular reactivity to give indole products, and intermolecular tandem catalytic routes have been developed to complete hydroamination/hydrosilylation sequences to realize secondary amine syntheses upon workup (Scheme 15.27) [188]. In this case, the Markovnikov products are obtained and enhanced catalyst efficiency is realized in the presence of weakly coordinating anions such as... 

The iridium complex 29, bearing a pincer ligand, was an efScient catalyst for the hydroamination/cyclization of secondary amines as shown in Equation (8.18). Remarkably, both Rh and Ir catalysts were found to be air and water stable, and no appreciable loss of catalytic activity was observed when carrying out the reaction in water as solvent. For example, the desired reaction product was observed in more than 98% yield (as observed by m NMR) using catalyst... 

As an alternative, iridium complexes show exciting catalytic activities in various organic transformations for C-C bond formation. Iridium complexes have been known to be effective catalysts for hydrogenation [1—5] and hydrogen transfers [6-27], including in enantioselective synthesis [28-47]. The catalytic activity of iridium complexes also covers a wide range for dehydrogenation [48-54], metathesis [55], hydroamination [56-61], hydrosilylation [62], and hydroalkoxylation reactions [63] and has been employed in alkyne-alkyne and alkyne - alkene cyclizations and allylic substitution reactions [64-114]. In addition, Ir-catalyzed asymmetric 1,3-dipolar cycloaddition of a,P-unsaturated nitriles with nitrone was reported [115]. 

Several metal complexes with CCC pincer-type dicarbene ligands have been investigated over the years by the group of Hollis as catalysts for the intramolecular hydroamination/cychzation of unactivated alkenylamines. Initial studies concerned rhodium(III) and iridium(III) complexes of type 75, but later investigations were extended to complexes of the same ligands with group 4 metals such as zirconium, hafnium, and tita-... 

IrCp iridium(iii) complexes containing a bidentate imidazolyl(NHC) or pyrimidyl(NHC) ligand have been used in the hydroamination/eyelisation of secondary amines, albeit with moderate activity when eompared to the best reported catalysts. The erucial role of steric bulk around the pendant nitrogen atom in these systems was established in order to get reasonable reactivity. ... 

Field LD, Messerle BA, Vuong KQ, Turner P. Rhodium(I) and iridium(I) complexes containing bidentate phosphine-imidazolyl donor ligands as catalysts for the hydroamination and hydrothiolation of alkynes. Dalton Trans. 2009 3599-3614. 

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. ... 

Zirconium Intermolecular hydroamination of both terminal and internal alkynes R C=CR with primary amines R NH2 to produce (after subsequent reduction) saturated secondary amines RiCH2-CH(NHR )R can be attained with the in situ generated zirconium catalysts (Me2N)4Zr (5 mol%) and sulfonamide (10 mol%). " Zirconium-catalysed intramolecular hydroamination (225) (226) has been studied theoretically " as for the analogous iridium-catalysed cyclization of (177) discussed (g) earlier " and similar conclusions have been reached regarding the hydrogen bonding, and so on. 

Krogstad DA, DeBoer AJ, Ortmeier WJ, Rudolf JW, Halfen JA (2005) l,3,5-Triaza-7-phosphaadamantane (PTA) ligated iridium(I) complexes as catalysts for the intramolecular hydroamination of 4-pentyn-l-amine in water. Inorg Chem Commun 8 1141-1144... 

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