Iridium catalysis amination

Scheme 7.20 Domino reductive amination catalysed by chiral phosphoric acid catalysis and chiral iridium catalysis.

Scheme 7.71 Tandem isomerisation-Michael reaction catalysed by iridium catalysis and chiral amine catalysis.

Aqueous organometalHc catalysis allows the use of NH3-solutions in water for the direct synthesis of amines from olefins in a combined hydroformylation/reductive amination procedure (Scheme 4.19). The hydroformylation step was catalyzed by the proven Rh/TPPTS or Rh/BINAS (44) catalysts, while the iridium complexes formed from the same phosphine ligands and [ IrCl(COD) 2] were found suitable for the hydrogenation of the intermediate imines. With sufficiently high NH3/olefin ratios (8/1) high selectivity towards the formation of primary amines (up to 90 %) could be achieved, while in an excess of olefin the corresponding... 

Cyclometallated iridium complexes, for OLEDs, 12, 145 Cyclometallated palladium(II) complexes from amines and pyridines, 8, 280 with C,C-chelating ligands, 8, 291 enantioselective synthesis, 8, 296 ferrocene-based palladacycles, 8, 292 four-membered palladacycles, 8, 297 imine- and oxime-based complexes, 8, 285 with N-N and N=N bonds, 8, 288 palladacycle catalysis, 8, 297... 

We have already alluded to the diversity of oxidation states, the dominance of 0x0 chemistry and the cluster carbonyls. Brief mention should be made too of the tendency of osmium (shared also by ruthenium and, to some extent, rhodium and iridium) to form polymeric species, often with oxo, nitrido or carboxylato bridges. Although it does have some activity in homogeneous catalysis (e.g. of CM-hydroxylation, hydroxyamination or amination of alkenes, see p, 558, and occasionally for isomerization or hydrogenation of alkenes, see p. 571), osmium complexes are perhaps too substitution-inert for homogeneous catalysis to become a major feature of the chemistry of the element. The spectroscopic properties of some of the substituted heterocyclic nitrogen-donor complexes may yet make osmium an important element for photodissociation energy research. 

In 2015, Zhao and co-workers described the first dynamic kinetic asymmetric amination of alcohols via borrowing hydrogen methodology under the cooperative catalysis of iridium complex 25 and chiral phosphoric acid 27 (Schemes 31, 32) [179]. The authors proposed that, initially, the two stereocenters in the alcohols were both racemized to ketone by the first oxidation, followed by tautomerization of the iminium intermediates 28 and 30 through enamine intermediate 29. Then, the... 

Zhang Y, Lim CS, Zhao Y et al (2014) Catalytic enantioselective amination of alcohols by the use of borrowing hydrogen methodology cooperative catalysis by iridium and a chiral phosphoric acid. Angew Chem Int Ed 53(5) 1399-1403... 

Bidentate coordination of the imine was also demonstrated in crystal structures of Ir(i) bis(ethylene) and 1,5-cyclooctadiene complexes. An analogous chelate iridium-amine adduct was also synthesized and structurally characterized. The kinetics of substitution of amine by imine (Scheme 14) were investigated to probe the mechanism of the product/substrate exchange reaction in the proposed catalytic cycle. The data were interpreted in terms of an associative mechanism in which the imine binds reversibly to Ir, prior to the release of amine. However, since the catalytic mechanism may well involve octahedral Ir(m) rather than square-planar Ir(i) complexes, a different mechanism could well operate during catalysis. 

Keywords Alcohols Amides Amines Carbon dioxide Catalysis Dehydrogenative coupling Esters Hydrogen Imines Iridium Metal-ligand cooperation O-H activation Pincer complexes PNN PNP Ruthenium... 

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