Ruthenium-catalyzed hydrogenation catalyst preparation

Mitsubishi have reported several processes based on Ru-catalyzed hydrogenation of anhydrides and acids. Succinic anhydride can be converted into mixtures of 1,4-butane-diol and y-butyrolactone using [Ru(acac)3]/trioctylphosphine and an activator (often a phosphonic acid) [97]. Relatively high temperatures are required ( 200°C) for this reaction. The lactone can be prepared selectively under the appropriate reaction conditions, and a process has been developed for isolating the products and recycling the ruthenium catalyst [98-100]. 

BINAP core-functionalized dendrimers were synthesized by Fan et al. (36), via condensation of Frechet s polybenzyl ether dendritic wedges to 5,5 -diamino-BINAP (26—28). The various generations of BINAP core-functionalized dendrimers were tested in the ruthenium-catalyzed asymmetric hydrogenation of 2-[p-(2-methyl-propyl)phenyl]acrylic acid in the presence of 80 bar H2 pressure and in a 1 1 (v/v) methanol/toluene mixture. As later generations of the in situ prepared cymeneruthe-nium chloride dendritic catalysts were used, higher activities were observed (TOF values were 6.5, 8.3, and 214 h respectively). Relative to those of the BINAP... 

In a related report, ruthenium-catalyzed enantioselective hydrogenation of 3-keto esters was utilized to prepare the crucial alcohol intermediate 36 (Scheme 14.16). The required (3-keto ester 49 was readily prepared from commercial thiophene carboxylic acid 40. Hydrogenation of 49 then led to the desired (S)-alcohol 50 in quantitative yield and 90% enantiomeric excess, catalyzed by a chiral diphosphine-ruthenium complex generated in situ. Catalyst-substrate ratios used were as low as 1/20,000, rendering this approach amenable to industrial application. Alcohol 50 was then converted to known intermediate 36 in three steps and 60% overall yield. 

A dominant feature of the type c ring-construction approach to azepine systems has been ruthenium-catalyzed ringclosing metathesis reactions. Examples include the synthesis of the azepine derivative 157 from 156 using either the Grubbs type I catalyst 159 or type II 160. The diene precursor 156 was prepared in turn from 154 via 155, as shown in Scheme 21. Hydrogenation of the C-C double bond in 157 afforded the azepane 158 <2005SL631>. 

Ruthenium-catalyzed hydrodimerization of acrylonitrile under hydrogen atmosphere to give adiponitrile (393) is a useful coupling reaction [154], Dimethyl hexenedioates (394a and 394b) are formed by dimerization of methyl acrylate by Pd, Ru and Rh catalysts. In particular the catalyst prepared by the treatment of RuC12 with Zn and... 

By contrast, much of the work performed using ruthenium-based catalysts has employed well-defined complexes. These have mostly been studied in the ATRP of MMA, and include complexes (158)-(165).400-405 Recent studies with (158) have shown the importance of amine additives which afford faster, more controlled polymerization.406 A fast polymerization has also been reported with a dimethylaminoindenyl analog of (161).407 The Grubbs-type metathesis initiator (165) polymerizes MMA without the need for an organic initiator, and may therefore be used to prepare block copolymers of MMA and 1,5-cyclooctadiene.405 Hydrogenation of this product yields PE-b-PMMA. N-heterocyclic carbene analogs of (164) have also been used to catalyze the free radical polymerization of both MMA and styrene.408... 

Enantioselective catalytic hydrogenation. The ruthenium(II) complexes of (R)- and (S)-l, bearing a chiral BINAP ligand, catalyze asymmetric hydrogenation of N-acyl-l-alkylidenetetrahydroisoquinolines to give (1R)- or (lS)-tetrahydroiso-quinolines in 95-100% ee.1 Thus the (Z)-enamide (2), prepared by acylation of 3,4-dihydropapaverine, is hydrogenated in the presence of (R)-l to (1R)-tetrahydroisoquinolines (3). The enantiomeric (lS)-3 is obtained on use of (S)-l as catalyst. 

Itsimo [25] has also shown that polymer-supported OPEN monosulfonamides containing sulfonated pendent group (Scheme 16) are able to catalyze the HTR reduction of ketones in water with sodium formiate as hydrogen donor (S/C = 100). However, TsDPEN immobilized on polystyrene crosslinked or not, polymer 30 and 31 respectively, shrank in water. Sodium /j-styrene sulfonate was copolymerized with chiral A-(vinylbenzene-p-sulfonyl)-DPEN (20) imder radical polymerization conditions with or without DVB leading respectively to ligand 32 and 33. Control of the balance hydrophilicity/hydrophobieity of the polymer support is carried out by changing the salt from Na to quaternary ammonium. All of these polymers swelled in water, and their respective ruthenium, rhodium or iridium complexes were prepared. Compared to sodium salt polymer-supported catalyst from 32a and 33a, ammonium... 

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