Catalysis iridium

Dickson, R. D., in Homogeneous Catalysis with Compounds of Rhodium and Iridium, Catalysis by Metal Complexes. D. Reidel Publishing Co., Dordrecht, 1985, pp. 40. 

The mechanism of iridium-catalyzed hydrogenation remains unclear. Although several experimental [31, 53, 54] and computational [53, 55, 56] studies have been reported recently, further investigations will be necessary to establish a coherent mechanistic model. Until now, most studies have dealt with simple test substrates hence, it will be important to explore more complex and also industrially important substrates, in order to determine the full scope and limitations of iridium catalysis. 

Phosphinite pincer iridium systems have also been shown to have a lower tendency to oxidatively add TEE to give (vinyl)(hydride) complexes similar to 3 [18]. While this has been identified as one of the major catalyst deactivation processes in phosphine pincer iridium catalysis, apparently with complexes such as 5, only olefin coordination can occur. However, this is a considerably weaker bonding and is less detrimental to catalyst activity. Eased on steric arguments, product olefin coordination (e.g. COE) is favored over TEE coordination, and therefore at a high TON and high product concentrations the phosphinite catalysts 5 are markedly less active than the phosphine analogues 1. 

Keywords Rhodium Iridium Catalysis Oppenauer-type oxidations ... 

Asymmetric hydrogenation of quinolines by iridium catalysis was explored <03JA10536>. Nineteen compounds were reported with excellent yields and enantiomeric excesses. 

Join B, Yamamoto T, Itami K (2009) Iridium catalysis for C-H bond arylation of heteroarenes with iodoarenes. Angew Chem Int Ed 48 3644-3647... 

C-H borylation is a widely used methodology for the synthesis of organoboronates [63-65]. Most of the applications have been presented for the synthesis of aryl-boronates. However, functionalization of alkenes has also attracted much interest [66, 67]. In most applications, iridium catalysis was used. However, in case of alkenes, borohydride forms as a side product of the C-H borylation, which undergoes hydroboration with alkenes. This side reaction can be avoided using palladium catalysis under oxidative conditions. In a practically useful implementation of this reaction, pincer-complex catalysis (Ig) was appHed (Figure 4.17) [51]. The reaction can be carried out under mild reaction conditions at room temperature using the neat aUcene 34 as solvent. In this reaction, hypervalent iodine 36, the TFA analog of 29, was employed. In the absence of 36, borylation reaction did not occur. 

A catalytic enantioselective vinylogous Reformatsky-aldol reaction exploits iridium catalysis, gives excellent regio-, diastereo-, and enantio-selectivities, and can be carried out with approximately equal facility from the alcohol or aldehyde oxidation level. 

Choi J, Goldman A (2011) Ir-catalyzed functionalization of C-H bonds. In Andersson PG (ed) Iridium catalysis, vol 34. Springer, Berlin/Heidelberg, pp 139-167... 

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). 

A 2008 paper from the Kami group noted the direct coupling of an aryl iodide to an unactivated aryl ring in the absence of transition metals typically employed for this purpose. The Itami group was attempting biaryl formation through the use of iridium catalysis with potassium t-butoxide as base, but control reactions found the reaction occurred solely in the presence of potassium t-butoxide. Optimized conditions of an aryl iodide with a variety of electron deficient heteroaromatic rings and potassium t-butoxide for 5 min under microwave conditions provided a number of successfully coupled biaryls. 

Scheme 3.11 Tandem dehydrogenation-aldol-dehydration-hydrogenation -dehydro-genation reaction catalysed by a combination of iridium catalysis and chiral ruthenium catalysis.

Scheme 7.20 Domino reductive amination catalysed by chiral phosphoric acid catalysis and chiral iridium catalysis.

Scheme 7.21 Domino hydrogenation of quinolines eatalysed by chiral phosphor-amide catalysis and iridium catalysis.

Scheme 7.71 Tandem isomerisation-Michael reaction catalysed by iridium catalysis and chiral amine catalysis.

The decarboxylative coupling of benzoic acids with internal alkynes in a 1 2 manner was achieved under iridium catalysis to produce the corresponding benzannu-lated products (Scheme 4.31) [36]. The carboxylic group acts as a directing group, as in the rhodium-catalyzed ortho-alkenylation described above (Schemes 4.28 and 4.29). Thus, carboxylic group directed metalation at the ortho C-H bond and subsequent alkyne insertion may take place to form a seven-membered iridacycle intermediate. Then, decarboxylation, the second alkyne insertion, and... 

---