Iridium hydrogen-transfer catalysis

Arylation, olefins, 187, 190 Arylketimines, iridium hydrogenation, 83 Arylpropanoic acid, Grignard coupling, 190 Aspartame, 8, 27 Asymmetric catalysis characteristics, 11 chiral metal complexes, 122 covalently bound intermediates, 323 electrochemistry, 342 hydrogen-bonded associates, 328 industrial applications, 8, 357 optically active compounds, 2 phase-transfer reactions, 333 photochemistry, 341 polymerization, 174, 332 purely organic compounds, 323 see also specific complexes Asymmetric induction, 71, 155 Attractive interaction, 196, 216 Autoinduction, 330 Axial chirality, 18 Aza-Diels-Alder reaction, 220 Azetidinone, 44, 80 Aziridination, olefins, 207... 

An iridium-mediated synthesis of pyrroles 17 was reported which was enabled by the development of Ir catalyst 18. This method allows for the smooth coupling of alcohols 16 and amino alcohols 15 through a dehy-drogenative process. Detailed mechanistic studies were conducted to identify all of the intermediates, side-products, and by-products of the reaction. It was proven that the catalytic cycle is base-promoted and hydrogen transfer shuttles are active in the system. It is important to note that this reaction can also be carried out under Ru catalysis albeit with lower reactivity (14JA4974). 

Saidi O, Williams JMJ. Iridium-catalyzed hydrogen transfer reactions. In Andersson PG, editor. Iridium catalysis. Volume 34. Topics in organometallic chemistry. Berlin Springer 2011. 

Whereas most hydrogenation catalysts function very well in water (see for example Chapter 38 for two-phase aqueous catalysis), scattered instances are known of inhibition by water. Laue et al. attached Noyori s transfer hydrogenation catalyst to a soluble polymer and used this in a continuous device in which the catalyst was separated from the product by a membrane. The catalyst was found to be inhibited by the presence of traces of water in the feed stream, though this could be reversed by continuously feeding a small amount of potassium isopropoxide [60]. A case of water inhibition in iridium-catalyzed hydrogenation is described in Section 44.6.2. 

In addition to transfer hydrogenation reactions, arene ruthenium complexes also display excellent activity in the catalytic hydrogenation of olefins and alkynes including asymmetric reduction [40]. Remarkably, this process occurs under milder conditions, than required for catalysis with the dissociation of arene-metal bond. Lately, arene iridium complexes have also been found to be effective hydrogenation catalysts [41 ]. It is noteworthy that iridium can also promotes addition to the carbon-nitrogen double bond. 

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