Iridium catalysis alkylation

The ability to harness alkynes as effective precursors of reactive metal vinylidenes in catalysis depends on rapid alkyne-to-vinylidene interconversion [1]. This process has been studied experimentally and computationally for [MC1(PR3)2] (M = Rh, Ir, Scheme 9.1) [2]. Starting from the 7t-alkyne complex 1, oxidative addition is proposed to give a transient hydridoacetylide complex (3) vhich can undergo intramolecular 1,3-H-shift to provide a vinylidene complex (S). Main-group atoms presumably migrate via a similar mechanism. For iridium, intermediates of type 3 have been directly observed [3]. Section 9.3 describes the use of an alternate alkylative approach for the formation of rhodium vinylidene intermediates bearing two carbon-substituents (alkenylidenes). 

Catalysis. Iridium compounds do not have industrial applications as catalysts. However, these compounds have been studied to model fundamental catalytic steps (174), such as substrate binding of unsaturated molecules and dioxygen oxidative addition of hydrogen, alkyl halides, and the carbon—hydrogen bond reductive elimination and important metal-centered transformations such as carbonylation, p-elimination, CO reduction, and... 

The formation of a branched chiral product from the alkylation of monosubstituted substrates is not limited to the catalysis of metals described thus far. Allylic alkylation reactions catalyzed with rhodium [211] and iridium [212] complexes have been shown to occur at the more... 

Iridium-carbon multiple bonds allenylidene complexes, 7, 355 carbene complexes, 7, 344 carbyne complexes, 7, 361 higher cumulenylidene complexes, 7, 358 vinylidene complexes, 7, 352 Iridium-carbon single-bonded complexes alkenyl complexes, 7, 319 alkyl and aryl complexes, 7, 303 in C-C bond-forming catalysis, 7, 335 characteristics, 7, 303... 

Review "cis-Alkyl and cis-Acylrhodium and Iridium Hydrides Model Intermediates in Homogeneous Catalysis"... 

Unlike the hydrogenation catalysts, most iridium catalysts studied for hydroformylation chemistry are not particularly active and are usually much less active than their rhodium counterparts see Carbonylation Processes by Homogeneous Catalysis). However, this lower activity was useful in utihzing iridium complexes to study separate steps in the hydroformylation mechanism. Using iridium complexes, several steps important in the hydroformylation cycle such as alkyl migration to carbon monoxide were studied. Another carbonylation reaction in which iridum catalysis appears to be conunercially viable is in the carbonylation of methanol. ... 

In addition to iridium and cobalt catalysis, and following the work initiated by Cavell et al. [138] on the alkylation of azolium salts, nickel-catalyzed alkylations of various heteroarenes (i.e., indoles [139], benzimidazoles [139], benzothiazoles [139], benzoxazoles [139], 1,3,4-oxadiazoles [140]) with olefins have been reported (Scheme 19.95 and Scheme 19.96). These reactions proved complementary to other methods because they proceeded with the Markovnikov regioselectivity with respect to the olefin. 

In a tandem isomerization/Prins strategy utilizing cooperative catalysis between an iridium(III) catalyst and a Bronsted acid, indole 182 underwent an isomerization/protonation sequence via a Prins-type oxocarbenium intermediate, with subsequent C—C bond formation to give oxepane-fused indole 183 (13AGE12910). Various anthranilic acids were coupled with chiral a-haloacids to afford N-acylated anthranilic acid intermediates which underwent cyclization to (3R)-3-alkyl-4,l-benzoxazepin-2,5-diones... 

In the last decade, iridium carbonyl complexes have found many applications in homogeneous and heterogeneous catalysis, as well as in photoluminescent and optoelectronic devices. These aspects will be described in the corresponding sections. Here are summarized the main developments in the synthesis, characterization, and some, although brief, descriptions of use of the most remarkable iridium mono-, di-, polycarbonyl and cluster complexes. Specific reactivity of alkyl, aryl iridium carbonyl complexes are dealt with in the appropriate paragraph in this chapter. 

Mentz, M., Modro, A.M., Modro, T.A. Solvation and metal ion effects on the structure and reactivity of phosphoryl compounds. Part 3. Alkali metal ion catalysis in the alkylation by phosphate esters. J. ChettL Res. (S) 1994, 46-47. Hendry, P, Sargeson, A.M. Base hydrolysis of the pentaamine (trimethylphos-phate)iridium(in) ion. J. Chem. Soc., Chem. Commun. 1984, 164—165. Wadsworth, W.S., Jr. Lewis acid catalyzed methanolysis of a phosphate triester. J. Org. Chem. 1981, 46(20), 4080-4082. 

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