Iridium complexes alkenic imines

Five-membered cyclometallated complexes similar to (191) are produced from the reaction between alkenic imines and iridium complexes. The reaction of alkenic imines with [Ir(Cl)(C8H,4)2]2 in the presence of cyclohexylphosphine yields complex (193),442 which, when treated with Cl2, undergoes substitution without Ir—C bond rupture to give (194 reaction 114).441 Azobenzene or its derivatives react with [Ir(Cl)(C8Hl4)2]2 in the presence of PR3 (R=Ph, cyclohexyl) according to reaction (112) to yield the cyclometallated complex (195).441,442... 

Pfaltz has recently reported a new class of chiral phosphanodihydrooxazole-iridium catalysts 34 for the enantioselective hydrogenation of imines [38]. Based on Crabtree s success using similar achiral catalysts for the hydrogenation of normally unreactive tri- and tetrasubstituted alkenes [39], Pfaltz has now found that chiral phosphanodihydrooxazole-iridium complexes 34a-g will hydrogenate phenyl-substituted alkenes with high enantioselectivity [40]. As shown in Table 7, the trisubstituted alkene 35 can be hydrogenated under mild conditions (50 bar H2 at 23 C) with superior results using complex 34f (333 1 substrate to catalyst, >99% conversion and 98% ee, entry 6 ). 

A large number of reports have concerned transfer hydrogenation using isopropanol as donor, with imines, carbonyls-and occasionally alkenes-as substrate (Scheme 3.17). In some early studies conducted by Nolan and coworkers [36], NHC analogues of Crabtree catalysts, [Ir(cod)(py)(L)]PF,5 (L= Imes, Ipr, Icy) all proved to be active. The series of chelating iridium(III) carbene complexes shown in Scheme 3.5 (upper structure) proved to be accessible via a simple synthesis and catalytically active for hydrogen transfer from alcohols to ketones and imines. Unexpectedly, iridium was more active than the corresponding Rh complexes, but... 

Only one paper has reported on catalytic asymmetric hydrogenation. In this study by Corma et al., the neutral dimeric duphos-gold(I)complex 332 was used to catalyze the asymmetric hydrogenation of alkenes and imines. The use of the gold complex increased the enantioselectivity achieved with other platinum or iridium catalysts and activity was very high in the reaction tested [195] (Figure 8.5). 

Examples of the insertions of alkenes or alk5mes into metal-amido bonds are also rare. Examples of the insertions of alkenes into tihe M-N bonds of isolated amido complexes include the reaction of a rhodium anilide complex with alkenes to form imines witii kinetic behavior that is consistent with migratory insertion,and the formal insertion of the strongly electrophilic acrylonitrile into a platinum anilide. Additional examples include reactions of a lanthanide-amido complex generated in situ, a catalytic carboamination process in which the stereochemistry implies insertions of olefins into amides, and a catalytic hydroamination that appears to occur through an aminoalkyl complex generated by S3m addition of the iridium and amido groups across the C=C bond of norbomene. 

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