Ruthenium complexes iridium complex catalysts

Isomerization of [(, )-3-alkoxy-l-propenyl]boronates to the corresponding 7-alkoxyallylboronates was catalyzed by ruthenium or iridium complexes.64 [IrH2(TFlF)2(PPh2Me)2]PF6 was the most efficient catalyst for selective preparation of (ftfy-alkoxyallylboronates (Scheme 37). 

In the hydrogenation of alkenes, rhodium-, ruthenium- and iridium-phosphine catalysts are typically used [2-4]. Rhodium-phosphine complexes, such as Wilkinson s catalyst, are effective for obtaining alkanes under atmospheric pres-... 

Asymmetric hydroformylations of all the above types have been achieved with rhodium catalysts enantioface- and enantiomer-discriminating hydroformylations also occur with cobalt and platinum catalysts whereas with ruthenium or iridium complexes only enantioface-discriminating synthesis has been reported up to now (see Sect. 2.1.4.). 

FIGURE 2 Comparison of methanol carbonylation rates as a function of water concentration for rhodium-complex, iridium-complex, and iridium/ruthenium-complex catalysts (190 °C, 28 bar, 30% MeOAc (w/w), 8.4% Mel (w/w), 1950 ppm Ir or equimolar Rh). Adapted with permission from Figure 1 in reference [125], copyright 2004, American Chemical Society. 

These reactions have been investigated since the 1970s. Palladium, rhodium, nickel, ruthenium, and iridium complexes proved to be active catalysts, but at first with only low conversions. In the 1990s, these reactions were picked up again, first by Graf and Leitner [84] with Rh catalysts, then by Jessop and co-workers [85] and Baiker and co-workers [86] with Ru complexes. An enormous increase in activity was achieved in the synthesis of formic acid a turnover frequency (TOF) of 95 000 h 1 was obtained and for DMF a TOF of 370 000h 1. 

The first use of a metal catalyst in the DKR of secondary alcohols was reported by Williams et al. [7]. In this work, various rhodium, iridium, ruthenium and aluminum complexes were tested. Among them, only Rh2(OAc)4 and [Rh(cod)Cl]2 showed reasonable activity as the racemization catalyst in the DKR of 1-phenylethanol. The racemization occurred through transfer-hydrogenation reactions and required stoichiometric amounts of ketone as hydrogen acceptor. The DKR of 1-phenylethanol performed with Rh2(OAc)4 and Pseudomonas Jluore-scens lipase gave (R)-l-phenylethyl acetate of 98%e.e. at 60% conversion after 72 h. 

Ir/tppts catalysts exhibit almost the same selectivity as Ru/tppts in the hydrogenation of a,p-unsaturated aldehydes albeit with approximately 70 times lower rates.485 In sharp contrast to the ruthenium and iridium based tppts catalysts, RhJ tppts complexes catalyse the chemoselective hydrogenation of a,fl-unsaturated aldehydes to the corresponding saturated aldehydes (Figure 14, III).54-485... 

As in years past, the published thiophene literature dwarfs the selenophene and tellurophene literature. However, there was a significant increase in the number of interesting selenophene and tellurophene references last year. The preparation of T)5-selenophene complexes of chromium, magnesium, ruthenium and iridium were studied <950M332>. These studies took advantage of the NMR-active selenium isotope 77Se (7.58% natural abundance) as a tool to directly study binding of selenophene derivatives to a catalyst surface. 

A range of metal catalysts have also been studied in aqueous solution for the transformation of carbon dioxide, including rhodium, ruthenium and iridium bipyridine or phenanthroline complexes.One of the most effective systems is the iridium complex shown in Figure 3.14. The ligand design concept used in this study is very clever. The catalytic activity of the complex and its solubility in aqueous solution can be tuned by the pH of the solution.Under acidic... 

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