Iridium dihydrido

In an alternative sequence suggested by Eisenberg et al. (80), X in Eq. (19) is hydride. C02 production then proceeds via /3-elimination from the oxygen OH in 18, giving a rhodium(III) dihydrido species which can then reductively eliminate H2. Some support for this latter suggestion is provided by the observation that iridium(lll) species of type 19, formed by oxidative addition of formic acid to /ra/ s-[IrCI(CO)L2] (L = tertiary phosphine), rapidly lose C02 to give the dihydrido species 20 (81). 

The main species in solution has been identified to be the hydrido-alkynyl complex [IrH(C2Ph)(cod)(//2-iPrPCH2CH2OMe)]+BF4 (23). This is, however, only a sink that results from direct reaction of 22 with the 1-alkyne, draining the active catalyst from the system. The catalysis proceeds via the dihydrido-diene intermediate [IrH2(cod)(//2- PrPCH2CH2OMe)]+ BF4 (24), which reacts reversibly with the alkyne to yield the hydrido-iridium-styryl complex 25, followed by a rate-determining reaction of this hydrido-vinyl species with hydrogen to re-... 

Dihydrido Iridium Triisopropylphosphine Complexes From Organometallic Chemistry to Catalysis... 

In contrast, 1,5-cyclo-octadiene remains coordinated during the catalytic cycle of hydrogenation of phenylacetylene to styrene, catalyzed by the related iridium complex [Ir(C0D)( Pr2PCH2CH20Me)]BF4. This complex, which contains an ether-phosphine-chelated ligand, catalyzes the selective hydrogenation reaction via a dihydrido-cyclo-octadiene intermediate. The reaction is first order in each of catalyst, phenylacetylene and hydrogen [11] the proposed catalytic cycle is shown in Scheme 2.3. 

The Dihydrido Iridium Triisopropylphosphine Complex [lrH2(NCMe)3(PPr3)]BF4 as Alkene Hydrogenation Catalysts... 

The Dihydrido Iridium Triisoprop/lphosphine Complex [irH2 NCMe), P Pr,)]BF4 23 BF4... 

A related dihydrido iridium complex of formula [(T -C6H5CH2CH2P Pr3-K-P)lrH2]BF4 [24] can be prepared by treatment of the dimer [Ir( x-OMe)(COD)]2 [15] with the phosphonium salt, [HPTr2CH2CH2QH5]BF4, in acetone followed by the reaction of hydrogen (Scheme 2.26). 

The functionalized phosphine coordinates to the iridium center as a 6+2 electron donor ligand. This dihydrido iridium]111) complex reacts with ethene or propene to yield ethane or propane and formation of the iridium(l) complexes [(t -QH5CH2CH2PTr2-K-P)lr(CH2=CHR)]BF4 (R=H, Me) (Scheme 2.27). 

Dihydrido Arene Iridium Triisopropylphosphine Complexes 33 CH2=CHR CH3CH2R... 

Dihydrido iridium Triisopropylphosphine Complexes as Imine Hydrogenation Catalysts... 

The dihydrido complex [RhH2(ri5-C5Me5)(PMe3)] forms C—H insertion products when irradiated in the presence of alkanes (ethane, propane).227,228 Reaction with CHBr3 leads to bromoalkylrhodium complexes, which on treatment with bromine give ethyl bromide or 1-bromopropane in 70-85% yield. The less stable iridium complex formed with neopentane could not be converted directly to neopentyl bromide.229 It gave, however, a mercury derivative that yielded the bromide after treatment with bromine. 

Dihapto 7>ligands, in copper complexes, 2, 174 Dihydride iridium complexes, preparation, 7, 396 Dihydrido clusters, with decarutheniums, 6, 1036 Dihydrobenzofuran, carbene C-H insertions, 10, 193 Dihydrobenzopyran, carbene C-H insertions, 10, 193 ring-closing diene metathesis,... 

Scheme 9.9 Preparation of the cycloalkyl(hydrido) and alkyl(hydrido) iridium(III) complexes 24a,b and 25a,b by intermolecular C—H bond activation from the dihydrido iridium(III) and the dicarbonyl iridium(I) compounds 21 and 22 as the precursors (a L = PMe3 b L = CO)...

Some unique structural types involving hydridic-protonic bonds were observed in triphenylphosphine complexes of iridium(III) [84, 88]. The reaction of IrH3(PPh3)3 with HBF4 in the presence of pyridinethione affords a dihydrido complex with a single hydridic-protonic contact, [IrH(H -HpyS-ii )(PPh3)3](BF4) (Scheme 3). 

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