Iridium amido complexes

Amido complexes. yd-H elimination from the monomeric iridium amido complex [Ir(NPhBz)(CO)(PPh3)2] has been observed and the products are the hydrido complex [IrH(CO)(PPh3)2] and PhCH=NPh. Kinetic studies indicate that dissociation... 

The iridium amido complexes (255) without P ligands, prepared from (256) and (257) by methanol elimination in THF, showed excellent enantioselectivities and activities in the asymmetric hydrogenation of simple ketones to alcohols. ... 

Iridium chemistry also holds a rare example of a monodentate guanidinate ligand. The monomeric parent amido complex Cp Ir(PMe3)(Ph)(NH2) cleanly undergoes an insertion reaction on treatment with diisopropylcarbodiimide (Scheme 153). Spectroscopic data and an X-ray structural analysis revealed the presence of a nonchelating guanidinate ligand. ... 

Deming T.J., Facile synthesis of block copol3fpeptides of defined architecture. Nature, 390, 386, 1997. Seidel S.W. and Deming T.J., Use of chiral mthenium and iridium amido-sulfonamidate complexes for controlled, enantioselective polypeptide synthesis. Macromolecules, 36, 969, 2003. 

Benzene—dienes, with pentarutheniums, 6, 986 Benzen/if/indenyl—amido complexes, with Ti(IV), 4, 438 j4-Benzenes with iridium, 7, 328 rhodium, 7, 181... 

The zirconocene bis(arylamido) complex 787 was obtained by the reaction of Cp2ZrCl2 with 2 equiv. of the lithium amide605 (Scheme 195). When the reaction is carried out in a 1 1 ratio, the monoamide zirconocene chloride is generated as the major product. Reaction of in situ-generated Cp 2Zr with 2-(methylmercapto)aniline yields monoamido zirconocene hydride 788, the spectroscopic data of which suggest an interaction between the S atom and the Zr center in this complex. The bis(amido) complex 787 serves as a precursor for the synthesis of amido rhodium and iridium complexes. 

The synthetic procedure is very critical. In our case, we believe that the imido-lithium compound (Li2NR) is present in the solution of butyl lithium and para-toluidine, in diethyl ether, as reported for the dilithiated a-naphtylamine. This is a noticeable difference in comparison to typical preparations of ruthenium, osmium, and iridium imido complexes, " in which a dichlorometal complex and the monolithium salt (LiNHR) in a molar ratio 1 2, appropriate for a ftA-amido precursor, are used. In these cases a subsequent removal of amine, or a dehydro-halogenation step with LiNHR, is required to afford the products and free amine. Equation (1) summarizes our synthetic procedure ... 

Finally, late-metal-amido complexes have been prepared by the oxidative addition of amines. These oxidative additions are included in Chapter 7. In brief, the oxidative addition of aniline is favored for several different types of metals. This reaction of electron-poor pentafluoroaniline to Pt(0) was reported many years ago by Stone (Equation 4.7), and the reaction of the parent aniline with Ir(PEt3)3Cl was reported later by Casalnuovo and Mil-stein. More recently, the oxidative addition of ammonia to an iridium(I) complex containing an electron-rich pincer ligand was observed (Equation 4.8). ... 

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. 

Equation 9.84 depicts the reaction of aniline, norbomene, and [Ir(PEt3)2(CjH )jCl] to form an iridium-aminoalkyl complex. This process is thought to occur by oxidative addition of the aniline to form an amido hydride complex, followed by insertion of the strained alkene into the iridium-nitrogen bond. Products from oxidative addition of aniline to the same iridium species were shown to form in the absence of the olefin. The syn stereochemistry of the aminoalkyl product indicated that a migratory insertion pathway was followed. 

P-Hydrogen elimination from the square-planar iridium(l) aUcoxo complexes shown at the top of Scheme 10.1 and p-hydrogen elimination from the iridium(l) amido complexes shown in Scheme 10.2 have been reported. Extensive mechanistic data on the elimination... 

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. 

Sieh D, Burger P. Formation of a stannyl amido complex by the reaction of a terminal iridium nitrido complex with a stannane. Z Anorg Allg Chem. 2015 641 52-55. Gloaguen Y, Rebreyend C, Lutz M, et al. An isolated nitridyl radical-bridged Rh(N-) Rh complex. Angew Chem Int Ed. 2014 53 6814-6818. 

Seidel SW, Eieming TJ (2003) Use of chiral rutheniiun and iridium amido-sulfoamidate complexes for controlled, enantioselctive polypeptide synthesis. Maraomolecules 36 969... 

Intriguing results in the area of N-H activation of amines promoted by iridium pincer complexes have been reported. " " In particular, Hartwig showed that, while the reaction of 328 with aniline gave [(PCP)IrH(NHPh)] 961, the analogous reaction with ammonia afforded the SQP NH3 complex [(PCP)Ir(NH3)] 962. In a separate experiment, it was shown that the amido hydride complex [(PCP)IrH(NH2)] 963, independently generated by deprotonation of the NH3 complex [(PCP)IrH(Cl)(NH3)] 964 with KN(SiMe3>2 at LT, underwent reductive elimination of NH3 at RT to form the NH3 complex 962. Remarkably, 963 would have been formed by oxidative addition of NH3. Some of this intriguing chemistry is presented in Scheme 132. 

Amido-bridged dinuclear iridium complexes, preparation,... 

Imidazolium ligands, in Rh complexes, 7, 126 Imidazolium salts iridium binding, 7, 349 in silver(I) carbene synthesis, 2, 206 Imidazol-2-ylidene carbenes, with tungsten carbonyls, 5, 678 (Imidazol-2-ylidene)gold(I) complexes, preparation, 2, 289 Imidazopyridine, in trinuclear Ru and Os clusters, 6, 727 Imidazo[l,2-a]-pyridines, iodo-substituted, in Grignard reagent preparation, 9, 37—38 Imido alkyl complexes, with tantalum, 5, 118—120 Imido-amido half-sandwich compounds, with tantalum, 5,183 /13-Imido clusters, with trinuclear Ru clusters, 6, 733 Imido complexes with bis-Gp Ti, 4, 579 with monoalkyl Ti(IV), 4, 336 with mono-Gp Ti(IV), 4, 419 with Ru half-sandwiches, 6, 519—520 with tantalum, 5, 110 with titanium(IV) dialkyls, 4, 352 with titanocenes, 4, 566 with tungsten... 

Complexes of the type [Ir(bzn)(cod)(L)](C104) (bzn = benzonitrile L = tricyclohexylphosphine, neomenthyldiphenylphosphine) catalyze the homogeneous hydrogenation of tetrasubstituted prochiral amido alkenes R R C=CR N. Under very mild conditions, the catalysis occurs for N = NHCOR, R = COjMe R = R = Me, R" = Me, Ph R = Me, R- = Ph, R = Me, Ph R = Ph, R = Me, R = Ph. [Ir(cod)(PCy3)(py)](PFg) serves as a catalyst in the hydroxyl-directed hydrogenation of cyclic and acyclic alkenic alcohols, wherein the reaction shows diastereoselectivity dependent on catalyst substrate stoichiometry. Park el have noted that the iridium(I)... 

Sato, Y., Kayaki, Y., and Ikariya, T. (2012) Efficient dynamic kinetic resolution of racemic secondary alcohols by a chemoenzymatic system using bifunctional iridium complexes with C-N chelate amido ligands. Chem. Commun. (Cambridge, UK), 48 (30), 3635-3637. 

Concerning ring size expansion, since the first anionic sbc-membered example derived from malonic acid described by Cesar et al. [8], other sophisticated five-[5a,9], sbc-[10], and seven-membered [11] NHCs have been described and coordinated to rhodium and iridium, including sbc-membered amino/amido carbenes [10b] and caffeine-based diamino carbenes [12]. Also related to this type of ligands, Conejero and coworkers described a general method for the preparation of 2-pyridylidene-based rhodium complexes by decarboxylation of pyridinium car-boxylates [13], a method previously described by Crabtree and coworkers [14]. 

Some iridium and riiodium amido and imido complexes have been synthesised in the group of Ahmed, and their reactivity partly explored [134, 196, 226-228], which may be models for some reactions involved in the catalytic cycles here discussed. However, the complexes themselves are not part of any established catalytic system and we will not discuss them any more. 

---