Hydrogenation alkynes and

NaH, LiAIHJ. For instance, they can act as reducing agents toward many organic compounds and are capable of hydrogenating alkynes and alkenes. Thus their H ligands are intermediate between the strictly hydridic hydrogens in the saline hydrides and the protonic hydrogens in compounds with nonmetals (e.g., HCI, NH3). 

The species [Ir(cod)(PPh3)(pz)] or [Ir(cod)(pz)]2 in the presence of PPhj (pz = pyrazolato) dissolves in acetone to yield catalytic solutions which partially hydroformylate and hydrogenate alkynes and alkenes. Results were reported for the hydroformylation of hept-2-yne. The hydrosilylation of styrene by [Si(Cl)2(H)Me] is catalyzed by complexes of the type [ML,L , ] (M = Ir, Co, Ni, Ru, Rh, Os, Pd, Pt L = halide, NO2 , SCN L = DMSO, Et2SO, Et2S, NHj). The catalytic activity and regioselectivity of these catalysts have been examined after immobilization on AVI 7X8 or KU 2X8 anion exchangers. ... 

The reaction occurs with stepwise addition of hydrogen to first give an alkene. The second step occurs even faster than the first. Therefore, catalytic hydrogenation with transition metal catalysts cannot be used to partially hydrogenate alkynes and stop at an alkene. The hydrogenation goes all the way to the alkane. 

An even more effective homogeneous hydrogenation catalyst is the complex [RhClfPPhsfs] which permits rapid reduction of alkenes, alkynes and other unsaturated compounds in benzene solution at 25°C and 1 atm pressure (p. 1134). The Haber process, which uses iron metal catalysts for the direct synthesis of ammonia from nitrogen and hydrogen at high temperatures and pressures, is a further example (p. 421). 

The special salt effect is a constant feature of the activation of substrates in cages subsequent to ET from electron-reservoir complexes. In the present case, the salt effect inhibits the C-H activation process [59], but in other cases, the result of the special effect can be favorable. For instance, when the reduction of a substrate is expected, one wishes to avoid the cage reaction with the sandwich. An example is the reduction of alkynes and of aldehydes or ketones [60], These reductions follow a pathway which is comparable to the one observed in the reaction with 02. In the absence of Na + PFg, coupling of the substrate with the sandwich is observed. Thus one equiv. Na+PFg is used to avoid this cage coupling and, in the presence of ethanol as a proton donor, hydrogenation is obtained (Scheme VII). 

Although hydrogenation of A-benzylideneaniline in the presence of 11 afforded the corresponding product (eq. 1 in Scheme 11), the a,(3-unsaturated ketone was converted into a mixture of unsaturated and saturated alcohols in the 42 56 ratio (eq. 2 in Scheme 11). Several substrates (nitrile derivatives, epoxides, esters, internal alkynes, and terminal alkenes), which are shown in Fig. 4, are not hydrogenated in this catalytic system. 

The catalytic system employing (2 - Fur)3P as ligand was applied to the coupling of methyl vinyl ketone and ethyl vinyl ketone to aromatic, aliphatic, acetylenic, and olefinic aldehydes (Scheme 23) [37]. Despite the hydrogenation conditions, alkyne and alkene moieties, as well as benzylic ether and nitro functional groups all remained intact. Furthermore, extremely high lev-... 

Baruwati, B., Polshettiwar, V. and Varma, R.S. (2009) Magnetically recoverable supported ruthenium catalyst for hydrogenation of alkynes and transfer... 

Fiirstner and coworkers developed a new Pt- and Au-catalyzed cycloisomerization of hydroxylated enynes 6/4-141 to give the bicylo[3.1.0]hexanone skeleton 6/4-143, which is found in a large number of terpenes [317]. It can be assumed that, in the case of the Pt-catalysis, a platinum carbene 6/4-142 is formed, which triggers an irreversible 1,2-hydrogen shift. The complexity of the product/substrate relationship can be increased by using a mixture of an alkynal and an allyl silane in the presence of PtCl2 to give 6/4-143 directly, in 55 % yield (Scheme 6/4.36). 

The mechanism of the methoxycarbonylation of alkynes667-669 promoted by the Pd(OAc)2/ PPh2(pyc)/CH3S03H catalytic system has been reported. Experiments carried out using 1-alkynes and CH3OD and 111 NMR reveal that the catalyst also promotes the exchange of the terminal hydrogen of the alkyne with the deuterium of the alcohol.677... 

The synthesis of cationic rhodium complexes constitutes another important contribution of the late 1960s. The preparation of cationic complexes of formula [Rh(diene)(PR3)2]+ was reported by several laboratories in the period 1968-1970 [17, 18]. Osborn and coworkers made the important discovery that these complexes, when treated with molecular hydrogen, yield [RhH2(PR3)2(S)2]+ (S = sol-vent). These rhodium(III) complexes function as homogeneous hydrogenation catalysts under mild conditions for the reduction of alkenes, dienes, alkynes, and ketones [17, 19]. Related complexes with chiral diphosphines have been very important in modern enantioselective catalytic hydrogenations (see Section 1.1.6). 

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