Hydroxides iridium complexes

The iridium complex 240 reacts with 2equiv of tetra- -butylammonium hydroxide to give the sulfoxide 252 and the methyl ketone 253 in 23% and 37% yields, respectively <2000CCR63>. The mechanism shown in Scheme 77 has been proposed. 

In the past, this field has been dominated by ruthenium, rhodium and iridium catalysts with extraordinary activities and furthermore superior enantioselectivities however, some investigations were carried out with iron catalysts. Early efforts were reported on the successful use of hydridocarbonyliron complexes HFcm(CO) as reducing reagent for a, P-unsaturated carbonyl compounds, dienes and C=N double bonds, albeit complexes were used in stoichiometric amounts [7]. The first catalytic approach was presented by Marko et al. on the reduction of acetone in the presence of Fe3(CO)12 or Fe(CO)5 [8]. In this reaction, the hydrogen is delivered by water under more drastic reaction conditions (100 bar, 100 °C). Addition of NEt3 as co-catalyst was necessary to obtain reasonable yields. The authors assumed a reaction of Fe(CO)5 with hydroxide ions to yield H Fe(CO)4 with liberation of carbon dioxide since basic conditions are present and exclude the formation of molecular hydrogen via the water gas shift reaction. H Fe(CO)4 is believed to be the active catalyst, which transfers the hydride to the acceptor. The catalyst presented displayed activity in the reduction of several ketones and aldehydes (Scheme 4.1) [9]. 

The hydroxide ion is a well-established bridging ligand, and hydroxo-bridged complexes of iridium(III) have been reviewed. Among the dinuclear iridium(I) complexes that have structures supported by 0H ligands is [Cp Ir(/u.-0H)3lrCp ]+, and closely related to this is (cod)Ir(/u.-OPh)2lr(cod). The presence of the three OH... 

The base hydrolysis of [Co(NHg)5(02CCF3)] + and the analogous complexes of rhodium, iridium, and chromium(IIT) appears to involve the concerted attack of two hydroxide ions—one bonding to the acyl carbon atom of the trifluoroacetato group, and the other deprotonating the first 58, 129). 

D. Intramolecular Attack of Hydroxide Ions Iridium(III) Complexes... 

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