Acetic acid catalysts, ruthenium complexes

From a practical standpoint, it is of interest to devise a one-step synthesis of the catalyst. Since both reactions 2 and 3 are ligand substitution reactions, it is quite conceivable that both steps can be carried out at the same time. When we reacted [Ru(COD)Cl2]n with BINAP and sodium acetate in acetic acid, we indeed obtained Ru(BINAP)(OAc)2 in good yields (70-80%). Interestingly, when the reaction was carried out in the absence of sodium acetate, no Ru(BINAP)(OAe)2 was obtained. The product was a mixture of chloro-ruthenium-BINAP complexes. A 3ip NMR study revealed that the mixture contained a major species (3) (31P [ H] (CDCI3) Pi=70.9 ppm P2=58.3 ppm J = 52.5 Hz) which accounted for more than 50% of the ruthenium-phosphine complexes (Figure 2). These complexes appeared to be different from previously characterized and published Ru(BINAP) species (12,13). More interestingly, these mixed complexes were found to catalyze the asymmetric hydrogenation of 2-(6 -methoxy-2 -naphthyl)acrylic acid with excellent rates and enantioselectivities. 

Paetzold and Backvall [27] have reported the DKR of a variety of primary amines using an analog of the ruthenium complex 1 as the racemization catalyst and isopropyl acetate as the acyl donor, in the presence of sodium carbonate at 90 °C (Fig. 9.17). Apparently, the function of the latter was to neutralize traces of acid, e.g. originating from the acyl donor, which would deactivate the ruthenium catalyst. 

A process for the coproduction of acetic anhydride and acetic acid, which has been operated by BP Chemicals since 1988, uses a quaternary ammonium iodide salt in a role similar to that of Lil [8]. Beneficial effects on rhodium-complex-catalyzed methanol carbonylation have also been found for other additives. For example, phosphine oxides such as Ph3PO enable high catalyst rates at low water concentrations without compromising catalyst stability [40—42]. Similarly, iodocarbonyl complexes of ruthenium and osmium (as used to promote iridium systems, Section 3) are found to enhance the activity of a rhodium catalyst at low water concentrations [43,44]. Other compounds reported to have beneficial effects include phosphate salts [45], transition metal halide salts [46], and oxoacids and heteropolyacids and their salts [47]. 

Aerobic oxidation of alkanes.1 Various metal complexes arc known to catalyze air oxidation of unactivatcd C-—H bonds. Murahashi et al. have found that both ruthenium and iron complexes arc useful catalysts for aerobic oxidation in combination with an aldehyde and an acid. Iron powder is the most effective catalyst, but FeCl3 6H2(), RuCI3 H20, and RuCI2[P(C6H5)3]3 can be used. Useful aldehydes arc hcptanal, 2-mcthylpropanal, and even acetaldehyde. A weak acid is suitable thus acetic acid is preferred to chloroacetic acid. By using the most satisfactory conditions, cyclohexane... 

Jn a potentially far reaching application for melt catalysis by the transition metals, we at Texaco have demonstrated the synthesis of a range of commodity chemicals and fuels directly from CO/H2 via the use of ruthenium-containing molten salt catalysis. Products include ethylene glycol, Ci-C4 alcohols, acetic acid, acetate esters, C2+ olefins and vicinal glycol esters. In its simplest form, this new class of melt catalyst comprises one or more ruthenium sources, e.g. ruthenium carbonyls, oxides, complexes, etc. dispersed in a low-melting (m.p. <150 C) quaternary phosphonium or ammonium salt (e.g. tetrabutylphos-phonium bromide). The key components are selected such that ... 

Today, dynamic kinetic resolution of secondary alcohols by combination of enzymes with transition metal catalysts, originally developed by Williams and Backvall, are perhaps the best developed methods (33-36). Hitherto the most successful catalyst designs have been based on half-sandwich ruthenium complexes, of which the pentaphenylcyclopentadienyl ruthenium complex has been claimed as the currently best racemization catalyst. Racemization is then based on reversible conversion of the alcohol into the corresponding ketone (Fig. 21, A). The dynamic kinetic resolution of 1-phenylethanol with isopropenyl acetate in toluene in the presence of Novozym 435, performed in preparative scale, is a good example of the use of ruthenium complexes (35). Another thoroughly studied racemization method (Fig. 21, B) is based on the use of acidic resins or zeolites. Here the racemization takes place through prochiral sp car-benium ion by simultaneous elimination and addition of water (37). The use of... 

The C-H bond activation process by Ru(OAc)2(p-cymene) and Pd(OAc)2 can be compared by kinetic study of their reaction with phenylpyridine leading in both cases to a cyclometallate complex. Although the reaction with Pd(OAc)2 is faster than with the ruthenium(II) catalyst, it is not affected by addition of acetic acid or acetate, thus the reaction with Pd(OAc)2 proceeds - to the difference of Ru(OAc)2L - via an intramolecular non-autocatalysed Concerted Metallation-Deprotonation (CMD) mechanism [91]. 

The above oxidation protocol was adapted to the formation C -CN bond of tertiary amines using RuCl3.nH20 as the ruthenium catalyst and oxygen in the presence of acetic acid as the oxidant at 60 C in a 3 1 methanol/acid acetic media (Scheme 33) [24]. Other ruthenium complexes were tested and RuCls, K2[RuCl5(H20)] and Ru2(OAc)4Cl were found to be excellent catalysts for the... 

Polycyclic ketones undergo Baeyer-VilUger oxidation with ammonium hexanitratocerate(IV) or cerium(IV) ammonium sulfate to afford lactones (Soucy et al., 1972 Mehta et al., 1976). The Baeyer-Villiger oxidation of adamantanone to the corresponding lactone is shown above in scheme 14. Camphorquinone is oxidized to a complex mixture of oxidation products (Danieli and Palmisano, 1976). Simple aliphatic ketones are not oxidized by cerium(IV) in the absence of a catalyst. In presence of ruthenium(III) chloride, cerium(IV) sulfate oxidizes 2-butanonone to acetic acid and formic acid, and 3-pentanone to a mixture of propionic acid, acetic acid and formic acid (Singh et al., 1980). 

The ruthenium carbene catalysts 1 developed by Grubbs are distinguished by an exceptional tolerance towards polar functional groups [3]. Although generalizations are difficult and further experimental data are necessary in order to obtain a fully comprehensive picture, some trends may be deduced from the literature reports. Thus, many examples indicate that ethers, silyl ethers, acetals, esters, amides, carbamates, sulfonamides, silanes and various heterocyclic entities do not disturb. Moreover, ketones and even aldehyde functions are compatible, in contrast to reactions catalyzed by the molybdenum alkylidene complex 24 which is known to react with these groups under certain conditions [26]. Even unprotected alcohols and free carboxylic acids seem to be tolerated by 1. It should also be emphasized that the sensitivity of 1 toward the substitution pattern of alkenes outlined above usually leaves pre-existing di-, tri- and tetrasubstituted double bonds in the substrates unaffected. A nice example that illustrates many of these features is the clean dimerization of FK-506 45 to compound 46 reported by Schreiber et al. (Scheme 12) [27]. 

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