Pyridines ruthenium carbonyl reactions

Our studies have focussed largely on the catalysis of the shift reaction by ruthenium carbonyl and by the ruthenium carbonyl/iron carbonyl mixtures in the presence of organic amines under low pressures of CO. Representative studies are indicated in Table II where it is notable that ruthenium alone is a considerably better catalyst than is iron alone. Among the ruthenium systems, pyridine solutions are somewhat more... 

Cobalt, nickel, iron, ruthenium, and rhodium carbonyls as well as palladium complexes are catalysts for hydrocarboxylation reactions and therefore reactions of olefins and acetylenes with CO and water, and also other carbonylation reactions. Analogously to hydroformylation reactions, better catalytic properties are shown by metal hydrido carbonyls having strong acidic properties. As in hydroformylation reactions, phosphine-carbonyl complexes of these metals are particularly active. Solvents for such reactions are alcohols, ketones, esters, pyridine, and acidic aqueous solutions. Stoichiometric carbonylation reaction by means of [Ni(CO)4] proceeds at atmospheric pressure at 308-353 K. In the presence of catalytic amounts of nickel carbonyl, this reaction is carried out at 390-490 K and 3 MPa. In the case of carbonylation which utilizes catalytic amounts of cobalt carbonyl, higher temperatures (up to 530 K) and higher pressures (3-90 MPa) are applied. Alkoxylcarbonylation reactions generally proceed under more drastic conditions than corresponding hydrocarboxylation reactions. 

Apart from halides, several neutral cocatalysts have been reported to increase the catalytic activity of Ruj(CO)i2 in carbonylation reactions of the kind here discussed [18, 19, 154, 170-172, 178-180]. In most cases, these cocatalysts are phosphines or heteroaromatic amines such as pyridine, Bipy or Phen, and are considered to act as ligands towards ruthenium. The question of the nuclearity of the active catalytic species has been examined only in the case of phosphines and it appears that the most active catalysts are mononuclear. In the case of nitrogen ligands, the question has not been examined in detail, but the same is probably also true. A more detailed discussion on this point is reported in Chapter 6. 

The use of palladium and ruthenium as halogen-free carbonylation catalysts has been studied intensively by Shell. The catalysts were principally designed for the carbonylation of olefins in the presence of alcohols in order to yield carboxylic esters [26], but work also well for the synthesis of carboxylic acids or anhydrides. The latter are formed when the reaction is conducted in an acid as a solvent [27]. The palladium systems typically consist of palladium acetate, tertiary phosphines, and strong acids such as mineral acids or acids with weak or noncoordinating anions such as p-toluenesulfonic acid. Remarkable activities are achieved when aromatic phosphines that carry pyridines as substituents are... 

The system is quite similar to the Pd-Py-Lewis acid catalysts above described. However while palladium in the presence o f a large excess o f pyridine alone is totally inactive in this reaction, palladium in the presence of 3,4,7,8-tetramethylphenantroline is able to catalyze the carbonylation of PhN02 to PhNHC02Et at 180 C and 40 atm (42.5 conversion and 51.5 < selectivity) when 2,4,6-trimethylbenzoic acid was also added to the catalytic system in a 8 to 1 ratio with palladium, the conversion reached lOOX, with more than 95X sel ect i v i ty [252]. Metals such as ruthenium, rhodium and platinum were much less active and selective under the same experimental conditions. 

In addition to palladium catalysts, ruthenium catalysts were applied in carbonylative C-H activation reactions as well. Moore and colleagues described the first ruthenium-catalyzed carbonylative C-H activation reaction in 1992 [52], Orf/io-acylation of pyridine and other nitrogen-containing aromatic compounds can be carried out with olefins and CO, using Ru3(CO)i2 as the catalyst (Scheme 6.16). Interestingly, internal olefins, such as cis- and frawi-2-hexene, yield the same linear/branched product ratio as terminal olefins. 

Porphyrin carbonyl complexes, like other metal carbonyls, undergo photodecarbonylation reactions. As an example, when the ruthenium(II) tetraphenylpor-phyrin complex Ru(TPP)(CO)py is photolyzed in the presence of pyridine, the bis-pyridine complex Ru(TPP)(py)2 is formed ... 

This reaction has been extended further to other porphyrins, and also to other axial ligands such as DMSO, THF, and amines. A similar photodecarbonylation is observed when the osmium(II) carbonyl complex Os(OEP)(CO)py is photolyzed in the presence of pyridine. Room temperature transient absorption studies on ruthenium(II) porphyrin carbonyl complexes show that there are significant differences in the nature of the lowest excited state for series of complexes having different axial ligands. For the complexes Ru(OEP)L2 and Ru(TPP)L2, where L is a (T-donor ligand such as pyridine, the complexes exhibit charge transfer... 

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