Hydrogen from iridium hydride

The dimerization of functional alkenes such as acrylates and acrylonitrile represents an attractive route to obtain bifunctional compounds such as dicarboxylates and diamine, respectively. The head-to-tail dimerizahon of acrylates and vinyl ketones was catalyzed by an iridium hydride complex generated in situ from [IrCl(cod)]2 and alcohols in the presence of P(OMe)3 and Na2C03 [26]. The reaction of butyl acrylate 51 in the presence of [IrCl(cod)]2 in 1-butanol led to a head-to-tail dimer, 2-methyl-2-pentenedioic acid dibutyl ester (53%), along with butyl propionate (35%) which is formed by hydrogen transfer from 1-butanol. In order to avoid... 

The photochemical studies of transition metal hydride complexes that have appeared in the chemical literature are reviewed, with primary emphasis on studies of iridium and ruthenium that were conducted by our research group. The photochemistry of the molybdenum hydride complexes Mo(tj5-C5H5)2M2] and [MoH4(dppe)2] (dppe = Ph2PCH2CH2PPh2), which eliminate H2 upon photolysis, is discussed in detail. The photoinduced elimination of molecular hydrogen from di-and polyhydride complexes of the transition elements is proposed to be a general reaction pathway. 

Gruber, S. Neuburger, M. Pfaltz, A. Characterization and reactivity studies of dinuclear iridium hydride complexes prepared from iridium catalysts with N, P and C, N ligands under hydrogenation conditions. Organometallics 2013,32,4702-4711. 

Successive hydrogen transfers within 60, followed by coordination of olefin and then H2 (an unsaturate route), constitute the catalytic cycle, while isomerization is effected through HFe(CO)3(7r-allyl) formed from 59. Loss of H2 from 60 was also considered to be photoinduced, and several hydrides, including neutral and cationic dihydrides of iridium(III) (385, 450, 451), ruthenium(II) (452) and a bis(7j-cyclopentadienyltungsten) dihydride (453), have been shown to undergo such reductive elimination of hydrogen. Photoassisted oxidative addition of H2 has also been dem-... 

The isomerization of the (Z)-isomer into the ( )-isomer promoted by the iridium complex explains the lack of stereospecificity of the transformation. O-Alkylated oximes and ketoximes do not react and this fact suggests that the presence of both hydrogen and a hydroxyl group is required for the success of the transformation. The authors proposed that the initial displacement of a chloride ion of the iridium complex by the oxime allows the iridium to remove both the oxygen and the hydride from the initial oxime. Swapping places of both substituents produces the amide. 

Transfer hydrogenation of aromatic ketones has been carried out in high yield and ee using propan-2-ol and a catalyst generated in situ from an iridium(I) [or rhodium(I)] hydride and a franx-l,2-diaminocyclohexane ligand.306... 

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