Ruthenium complexes supported catalysis

In the first part of this article, focusing attention on polymer-supported cobalt phosphine complex 1 and arene ruthenium complex 2, we review contributions from our laboratory that show how organometallics can be efficiently attached to derivitised polystyrene and we outline their synthetic versatility.2,3 Following this, we discuss the preparation of a supported ruthenium complex, 3, and its use in oxidation and transfer hydrogenation catalysis. 

Although ruthenium is significantly less expensive than rhodium and although its use has been recommended since 1960 (7) for the oxo synthesis, complexes of this metal have not been developed as catalysts. However, many papers and patents have referred to the results obtained employing various ruthenium complexes. The purpose of this article is to analyze the work done involving ruthenium compounds, restricting the scope only to the hydroformylation reaction and not to the carbonylation reaction, which would demand to too lengthy an article. In this review we examine successively mononuclear ruthenium complexes, ruthenium clusters as precursors, photochemical activation, and supported catalysis. 

Ruthenium complexes attract recent interest as new promising candidates for efficient, specific and environmentally benign allylation catalysts. It is noticeable that some J7 -allylruthenium(II) complexes have an ambiphilic property in catalysis involving the C-0 bond activation [52]. When allyl carboxylates or carbonates are treated with nucleophilic 1,3-dicarboxylates or electrophilic aldehyde in the presence of Ru complexes, catalytic allylations of nucleophiles or electrophiles take place [53]. In both reactions, J7 -allylruthenium complexes are assumed to be intermediates. Independent synthesis and reactions of the model compounds support this observation (Scheme 3.28). This ambiphilicity of the allylruthenium(II) may arise from the different reactivity of and rf forms in the allylic moiety [54]. 

Aromatic ketimines are reduced enantioselectively to amines (50 atm H2/toluene/65°C/24h), using a cooperative catalysis involving Knolker s iron complex and a BINOL-derived hydrogen phosphate auxiliary, with P-NMR evidence supporting the bifunctional catalysis. A phosphine-free chiral cationic ruthenium complex catalyses enantioselective hydrogenation of IV-alkyl ketimines, including many heretofore problematic substrates. 0... 

Astruc and coworkers [69] took this type of catalysis a step further when they developed a recyclable Ru(II) complex that was supported on magnetic nanoparticles. The cattilyst was prepared by immobilizing a pentamethylcyclopentadienyl ruthenium complex on iron oxide nanoparticles. 

Lindner, E Kemmler, M Mayer, H.A., and Wegner, P. (1994) Supported organo-metallic complexes. 5. Polysiloxane-bound ether-phosphines and ruthenium complexes. A characterization by solid-state NMR spectroscopy and catalysis. J. Am. Chem. Soc., 116, 348-361. 

Dihydropyrroles have recently become readily available by ring-closing metathesis. For this purpose, N-acylated or N-sulfonylated bis(allyl)amines are treated with catalytic amounts of a ruthenium carbene complex, whereupon cyclization to the dihydropyrrole occurs (Entries 6 and 7, Table 15.3 [30,31]). Catalysis by carbene complexes is most efficient in aprotic, non-nucleophilic solvents, and can also be conducted on hydrophobic supports such as cross-linked polystyrene. Free amines or other soft nucleophiles might, however, compete with the alkene for electrophilic attack by the catalyst, and should therefore be avoided. 

SAPC can perform a broad spectrum of reactions such as hydroformylation, hydrogenation and oxidation, for the synthesis of bulk and fine chemicals, pharmaceuticals and their intermediates. Rhodium complexes are the most extensively used, but complexes of ruthenium, platinum, palladium, cobalt, molybdenum and copper have also been employed [63-65]. Owing to interfacial reactions, one of the main advantages of SAPC upon biphasic catalysis is that the solubility of the reactant in the catalytic aqueous-phase does not limit the performance of the supported aqueous phase catalysts. 

Since the researcher normally looks to the chemistry of soluble complexes in designing polymer-bound catalysts, it is notable that some areas that have proven fruitful in homogeneous catalysis have been omitted from investigations using polymer-bound catalysts. One of these areas concerns the reactions of arenes. Benzene, for example, may be hydrogenated with homogeneous cobalt phosphite and ruthenium phosphine complexes, but the corresponding supported versions are not reported. Aryl halides may be carboxylated in the presence of a soluble palladium catalyst ... 

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