Hydrogenation quinolines

Using as catalyst precursors the clusters Os3H2(CO)i0 and Os3(CO)12 [71, 72], Laine and coworkers found a deuteration pattern of quinoline hydrogenation similar to that shown in Scheme 16.16, except for the presence of more deuterium in the 4-position and less in the 2-position, which has been interpreted in terms of the occurrence of oxidative addition of the osmium cluster to C-H bonds in quinoline, and also 1,4-hydrogenation (Scheme 16.17). 

Benzo[/i]quinolines hydrogenation, 2, 329 Skraup synthesis, 2, 467 structure, 2, 110 synthesis, 2, 468 from benzindoline, 2, 491 from propargylnaphthylamines, 2, 416 Benzoquinolinium cations metabolism, 1, 234 Benzoquinolinium salts Beyer synthesis, 2, 474 Benzoquinolinones synthesis, 2, 448... 

Recently. Alvarado et al. reported a related set of active catalysts for quinoline hydrogenation, formed in situ by addition of pyrazolylborate ligands Tp, hydrotris(pyrazolyl)borate and Tp. hydrotris(3,5-dimethylpyrazolyl)borate -which are isolectronic with cyclopentadienyl ligands- to [M(COD)C1]2 (M = Rh, Ir, COD = 1,5-cyclooctadiene), [Ir(COE)Cll2 (COE = cyclooctenc), and RuCl2(NCMe)4. Again, rhodium turned out to be the most efficient metal, and the activity was related with the ease of formation of Tp or Tp complexes. No mechanistic details were provided [101]. 

Similar metal-phosphine derivatives previously shown to be good catalysts for C=C and C=O bond reduction, were reported by Sanchez-Delgado and Gonzalez [78] to be efficient also for quinoline hydrogenation at 150° C and 30 atm Hj. The order of activity observed was ... 

The most relevant elementary steps involved in all the important quinoline hydrogenation catalysts are represented in Fig. 3.12 in the form of a generic catalytic cycle for both dihydride and monohydride catalysts that may be easily applied to other N-heterocyclic substrates. A number of points concerning these mechanisms are noteworthy ... 

Fig. 3 12. The mechanism of quinoline hydrogenation by (a) dihydride and (b) nionohydride catalysts.

In situ regioselective quinoline hydrogenation with transition metal complexes, such as [Rh(COD)Cl2], [Ir(COD)Cl2], [IrfCOE Ch], and [Ru(MeCN)4Cl2] stabilized by Tp and Tp ligands via one-pot reaction has been described. The results have been compared with those obtained with [Ir(Tp)(C2H4)2]. The system [Rh(COD)Cl2]/Tp is the most efficient and regioselective catalyst precursor for this reaction.65... 

Homogeneous hydrogenation of Q to THQ is also catalyzed by Os3(CO)j2 and its derivatives. These studies, together with the synthesis of osmium cluster complexes of quinoline, have led to another mechanism for quinoline hydrogenation which involves more than one metal center. It is likely that reactions catalyzed by Cp Rh(NCMe)3 and Os3(CO)i2 proceed by different mechanisms. Whether either of these mechanisms is consistent with the heterogeneously catalyzed conversion of Q to THQ is unknown. 

Palladium-calcium carbonate/quinoline Hydrogenation of acetylene derivatives partial and selective s. 16, 80 Palladium-strontium carbonate Partial ring hydrogenation of isocyclics s. 17, 89... 

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