Iridium catalysis substitution

With iridium catalysis, the -rr-allyl intermediate is attacked by the nucleophile at the more-substituted terminus. Again, the inclusion of a chiral ligand yields an optically active product (Scheme 9.66). 

Keywords Allylic substitution Asymmetric catalysis Heterocycles Iridium Phosphoramidite... 

We have already alluded to the diversity of oxidation states, the dominance of oxo 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 m-hydroxylation, hydroxyamination or animation 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. 

A related iridium complex has been used for the decarbo)grlative radical allylation of aminoacids and phenylacetic acids that occurs smoothly at room temperature in the presence of Pd(PPh3)4, irradiating by white LEDs. The proposed scheme (Scheme 6) is based on dual catalysis. Ruthenium tris(phenanthroline) dichloride has been used for visible light catalysis of the mild amidation of ketoacids by ort/zo-substituted anilines using ozygen as terminal oxidant (Scheme 7) ... 

Dodecacarbonyltetrairidium is the starting material for the synthesis of a large number of substitution products and of most anionic iridium carbonyl cluster compounds. Possible uses in catalysis of carbonyl and its substituted derivatives is also emerging. ... 

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. 

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