Water solubility organometallic compounds

Darensbourg, D.J. Joo, F. Kannisto, M. Katho, A. Reibenspies, J.H. Daigle, D.J.(1994) Water-soluble organometallic compounds. 4. Catalytic-hydrogenation of aldehydes in an aqueous 2-phase solvent system using a l,3,5-triaza-7-phosphaadamantane complex of ruthenium, Inorg. Chem., 55,200-8. 

Schibli R, Katti KV, Volkert WA, Barnes CL (2001) Development of novel water-soluble, organometallic compounds for potential use in nuclear medicine synthesis, characterization, and H and P NMR investigations of the complexes /phosphino)ethane, bis(bis(hydroxymethyl)phosphino)benzene). Inorg Chem... 

Darensbourg DJ, Robertson JB, Larkins DL, Reibenspies JH (1999) Water-soluble organometallic compounds. 7. Further studies of l,3,5-triaza-7-phosphaadamantane derivatives of group 10 metals, including metal carbonyls and hydrides. Inorg Chem 38 2473—2478... 

Darensbourg DJ, J06 F, Kannisto M, Katho A, Reibenspies JH (1992) Water-soluble organometallic compounds. 2. Catalytic-hydrogenation of aldehydes and olefins by new water-soluble l,3,5-tiiaza-7-phosphaadaiiiantane complexes of luthenium and rhodium. Oiganometallics 11 1990-1993... 

Darensbourg DJ, Stafford NW, J06 F, Reibenspies JH (1995) Water-soluble organometallic compounds. 5. The regioselective catalytic-hydrogenation of unsaturated aldehydes to saturated aldehydes in an aqueous 2-phase solvent system using 1,3,5-triaza-7-phosphaadamantane complexes of rhodium. J Organomet Chem 488 99-108... 

The Lo-Cat process, licensed by US Filter Company, and Dow/Shell s SulFerox process are additional liquid redox processes. These processes have replaced the vanadium oxidizing agents used in the Stretford process with iron. Organic chelating compounds are used to provide water-soluble organometallic complexes in the solution. As in the case of Stretford units, the solution is regenerated by contact with air. 

As is wdl known, the solubility of apolar guest compounds in water is (in general) increased when they forms indusion complexes with CyD. Thus, CyDs are potent phase-transfer catalysts [29]. Applications to organometallic catalysis are especially attractive from practical viewpoints [30]. As shown in Fig. 4.5, CyDs form inclusion complexes with hydrophobic substrates (S) at the Uquid/liquid interface and transfer them into the aqueous phase where they contact the water-soluble organometallic catalyst. After the reaction, the product (P) is released in the organic phase and the transfer cycle can go on. 

Makihara,N., Ogo, S. and Watanabe, Y., pH-selective hydrogenation of water-soluble carbonyl compounds and alkenes with [Cp Ir(III)(H20)3] (Cp = tj -CsMes) as a catalyst precursor in very acidic media, Organometallics, 2001, 20, 497. 

Indeed, these reactions proceed at 25 °C in ethanol-aqueous media in the absence of transition metal catalysts. The ease with which P-H bonds in primary phosphines can be converted to P-C bonds, as shown in Schemes 9 and 10, demonstrates the importance of primary phosphines in the design and development of novel organophosphorus compounds. In particular, functionalized hydroxymethyl phosphines have become ubiquitous in the development of water-soluble transition metal/organometallic compounds for potential applications in biphasic aqueous-organic catalysis and also in transition metal based pharmaceutical development [53-62]. Extensive investigations on the coordination chemistry of hydroxymethyl phosphines have demonstrated unique stereospe-cific and kinetic propensity of this class of water-soluble phosphines [53-62]. Representative examples outlined in Fig. 4, depict bidentate and multidentate coordination modes and the unique kinetic propensity to stabilize various oxidation states of metal centers, such as Re( V), Rh(III), Pt(II) and Au(I), in aqueous media [53 - 62]. Therefore, the importance of functionalized primary phosphines in the development of multidentate water-soluble phosphines cannot be overemphasized. 

Nowadays we look with other eyes at organometallic compounds the family of which has expanded enormously. Some members of this family are soluble in water due to their ionic nature the legions of anionic carbonylmetallates (e.g. [Ni(CN)(CO)3] ) and cationic bisphosphine Rh-chelate complexes (e.g. [Rh(BDPP)(COD)] ) just come to mind. Others obtain their solubility in water from the well soluble ligands they contain these can be ionic (sulfonate, carboxylate, phosphonate, ammonium, phosphonium etc. derivatives) or neutral, such as the ligands with polyoxyethylene chains or with a modified urotropin structure. 

At the end of this Chapter, looking at the exceptional variety of water-soluble ligands and the pace with which newer and newer compounds are synthetized it is safe to state that every aqueous reaction may find its perfect catalyst - at least the ligands are out there already. It seems that high-throughput screening could benefit aqueous organometallic catalysis, too. 

Indium-promoted organometallic reactions are greatly accelerated in water, especially when the coreactant carbonyl compound also has good water solubility. Otherwise, aqueous tetrahydrofuran can be used. To date, indium is the most effective metal for promoting Barbier-type reactions under aqueous conditions. As illustrated here, this is of particular value where formaldehyde is concerned, since the need to generate monomeric formaldehyde by thermal cracking is avoided. 

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