Iridium-catalyzed carbonylation

Scheme 2. Catalytic cycles for the iridium-catalyzed carbonylation of methanol.

There have been many reports of the use of iridium-catalyzed transfer hydrogenation of carbonyl compounds, and this section focuses on more recent examples where the control of enantioselectivity is not considered. In particular, recent interest has been in the use of iridium A -heterocyclic carbene complexes as active catalysts for transfer hydrogenation. However, alternative iridium complexes are effective catalysts [1, 2] and the air-stable complex 1 has been shown to be exceptionally active for the transfer hydrogenation of ketones [3]. For example, acetophenone 2 was converted into the corresponding alcohol 3 using only 0.001 mol% of this... 

Under the conditions of iridium-catalyzed hydrogenation, alkyne-carbonyl and alkyne-imine reductive coupling occurs in the absence of stoichiometric byproducts. For example, iridium-catalyzed hydrogenation of nonconjugated alkynes in the presence of ot-ketoesters delivers the corresponding a-hydroxy esters in... 

Scheme 9 Catalytic carbonyl addition via iridium-catalyzed hydrogenative coupling of dimethy-lallene...

Scheme 11 Carbonyl tert-prenylation, crotylation, and allylation from the aldehyde or alcohol oxidation level under the conditions or iridium-catalyzed transfer hydrogenation...

Scheme 13 Enantioselective carbonyl tert-prenylation from the alcohol or aldehyde oxidation level via iridium-catalyzed C-C bond-forming transfer hydrogenation...

Scheme 17 Carbonyl arylallylation from the alcohol oxidation level via iridium-catalyzed transfer hydrogenation employing alkynes as allyl donors...

Scheme 22 1, n-Glycols as dialdehyde equivalents in iridium-catalyzed enantioselective carbonyl allylation from the alcohol oxidation level... 

A wide range of carbon, nitrogen, and oxygen nucleophiles react with allylic esters in the presence of iridium catalysts to form branched allylic substitution products. The bulk of the recent literature on iridium-catalyzed allylic substitution has focused on catalysts derived from [Ir(COD)Cl]2 and phosphoramidite ligands. These complexes catalyze the formation of enantiomerically enriched allylic amines, allylic ethers, and (3-branched y-8 unsaturated carbonyl compounds. The latest generation and most commonly used of these catalysts (Scheme 1) consists of a cyclometalated iridium-phosphoramidite core chelated by 1,5-cyclooctadiene. A fifth coordination site is occupied in catalyst precursors by an additional -phosphoramidite or ethylene. The phosphoramidite that is used to generate the metalacyclic core typically contains one BlNOLate and one bis-arylethylamino group on phosphorus. 

Figure 8.3 (a) Catalytic cycle for the iridium-catalyzed methanol carbonylation (b) catalytic cycle for the iridium-catalyzed water gas shift (WGS) reaction. Both as originally proposed by D. Forster (adapted from Ref [25]). 

Figure 8.4 Methanol-assisted migratory CO insertion in the iridium-catalyzed methanol carbonylation (adapted from Refs [37, 38]).

Figure 8.6 Main step showing the role of the cocatalyst in the iridium-catalyzed methanol carbonylation reaction.

Murakami and Ito reported a novel iridium-catalyzed carbonylative ring expansion of allenylcyclopropanes [29]. When a mixture of substituted allenylcyclo-propane 49a (R = R = Et, R = R = H) and 5 mol% of IrCl(CO)(PPh3)2 in xylene is heated at 130°C under 5 atm pressure of CO for 35 h, cyclohexenone 53 a is obtained in 81% yield. The reaction is proposed to proceed through in-... 

Reaction (78) regenerates Mel from methanol and HI. Using a high-pressure IR cell at 0.6 MPa, complex (95) was found to be the main species present under catalytic conditions, and the oxidative addition of Mel was therefore assumed to be the rate determining step. The water-gas shift reaction (equation 70) also occurs during the process, causing a limited loss of carbon monoxide. A review of the cobalt-, rhodium- and iridium-catalyzed carbonylation of methanol to acetic acid is available.415... 

Methane, C-H activation, via palladium carbenes, 8, 243 Methanol carbonylations to acetic acid, 1, 133 iridium-catalyzed... 

An important feature of the present reaction is the chemoselective addition of activated nitriles to the CN triple bonds of nitriles in the presence of carbonyl groups, because of the strong coordination ability of nitriles toward metals. The iridium-catalyzed addition of ethyl cyanoacetate to 4-acetylbenzonitrile (30) gives ethyl (Z)-3-(4-acetylphenyl)-3-amino-2-cyano-2-propenoate (31, 59%) chemoselec-tively, while the same reaction promoted by a conventional base such as AcONH4 and NaOH gives ethyl 2-cyano-3-(4-cyanophenyl)-2-butenoate (32) ( Z= 55 45) [20]. 

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