Ferrate catalyst

Scheme 3 Cross-coupling with Gaertner s ionic liquid ferrate catalyst 13 [3]...

The replacement of a halogen by a low-valent ferrate catalyst is the key step in an intramolecular Heck-type reaction using both alkyl and aryl halides (Scheme 7.7) [11]. 

Oxidants commonly used include ozone, permanganate, chlorine, chlorine dioxide, and ferrate, often in combination with catalysts. Standard-type mixed reactors are used with contact times of several minutes to an hour. Special reactors for use with ultraviolet light have been developed. 

Acidic chloroaluminate ionic liquids have already been described as both solvents and catalysts for reactions conventionally catalyzed by AICI3, such as catalytic Friedel-Crafts alkylation [35] or stoichiometric Friedel-Crafts acylation [36], in Section 5.1. In a very similar manner, Lewis-acidic transition metal complexes can form complex anions by reaction with organic halide salts. Seddon and co-workers, for example, patented a Friedel-Crafts acylation process based on an acidic chloro-ferrate ionic liquid catalyst [37]. 

Until now examples for catalytic reactions involving ferrates with iron in the oxidation state of -l-3 are very rare. One example is the hexacyanoferrate 8-catalyzed oxidation of trimethoxybenzenes 7 to dimethoxy-p-benzoquinones 9/10 by means of hydrogen peroxide which was published by Matsumoto and Kobayashi in 1985 [2]. Using hexacyanoferrate 8 product 9 was favored while other catalysts like Fe(acac)3 or Fe2(S04)3 favored product 10 (Scheme 2). The oxidation is supposed to proceed via the corresponding phenols which are formed by the attack of OH radicals generated in the Fe/H202 system. 

One of the most prominent characteristics of Fe(+2) is its ability to undergo oxidation leading to Fe(+3). This was used by Uchiyama et al. when they reported on Fe(+2)-ate complexes as potent electron transfer catalysts [7, 8]. These ferrates are accessible from FeCl2 and 3 equiv. of MeLi. The Fe(+2/+3) oxidation potential of [Me3Fe(+2)]Li 19 in THF is —2.50 V, thus being in between those of Sml2 (—2.33 V) and Mg (—3.05 V). With these alkyliron-ate complexes it was possible to realize a reductive desulfonylation of various A -sulfonylated amines 20 with different basicity. By using Mg metal to restore the active Fe(+2) species 19 a catalytic reductive desulfonylation process was achieved (Scheme 4). 

Equally to ferrate 38 ferrates 39 and 40 also catalyze Alder-ene cycloisomeriza-tions [17]. Compared to 38, they require somewhat longer reaction times, possibly due to the chelating cod-hgand, which is more difficult to substitute by the en)me. The presence of cod in the reaction turns out to be of advantage with more demanding substrates like acyclic enynes with a terminal aUcene moiety where ferrate 38 is not reactive. Cod is assumed to stabilize the catalyst in its resting state as ancillary hgand. 

Practical interest in high-molecular-weight poly (propylene oxide) centers in its potential use as an elastomer (19). Copolymerization of propylene oxide with allyl glycidyl ether gives a copolymer with double bonds suitable for sulfur vulcanization. Table IV shows the properties of elastomers made with a copolymer prepared with a zinc hexacyano-ferrate-acetone-zinc chloride complex. Also shown are the properties of elastomers made from partially crystalline copolymers prepared with zinc diethyl-water catalyst. Of particular interest are the lower room-... 

Selective oxidation materials fall into two broad categories supported systems and bulk systems. The latter are of more practical relevance although one intermediary system, namely vanadia on titania [92,199-201], is of substantial technical relevance. This system is intermediary as titania may not be considered an inert support but rather as a co-catalysts [202] capable of, for example, delivering lattice oxygen to the surface. The bulk systems [100, 121, 135, 203] all consist of structurally complex oxides such as vanadyl phosphates, molybdates with main group components (BiMo), molybdo-vanadates, molybdo-ferrates and heteropolyacids based on Mo and W (sometimes with a broad variation of chemical composition). The reviews mentioned in Table 1.1 deal with many of these material classes. 

Scheme 7.26 Allylic alkylation using Fe2(CO)9 as the catalyst - in situ generation of a ferrate.

Trialkyl ferrates(II) or the related manganese(II) and cobalt(II) compounds are excellent catalyst for reduction of organic compounds by dissolved metals such as magnesium. The protocol provides for tuning of catalytic activity by way of metal and ligand.304... 

Fiirstner reported in parallel coupling reactions using 5 mol% of the isolated ferrate(-II) catalyst [Li(TMEDA)]2[Fe(C2H4)4] 4 in THF (Fig. 2) (entry 2) [45, 46], Primary and secondary alkyl bromides and iodides and allylic halides worked well, while alkyl chlorides and tertiary alkyl iodides were inert. Many sensitive functionalities like ester, nitrile, isocyanate, epoxide, and amine groups are tolerated. 

B Coq, G Ferrat, F Figueras. Conversion of chlorobenzene over palladium and rhodium catalysts of widely varying dispersion. J. Catal. 101 434-445,1986. 

Thus ferricyanide hydrolyzes photochemically to aquopentacyanoferrate which is a slightly better catalyst for decomposition than ferricyanide. On addition of ferrocyanide the ferrate is reduced to the ferrite which is more active. Some confirmation of these reactions is given by the observations that addition of the ferrate to ferricyanide increases the dark rate, and also that cyanide, nitrate, and nitrosobenzene inhibit this as well as the catalysis induced by irradiation of ferricyanide. 

Fig. 21. Activities of LaB03 (B, first-row transition element) perovskites for CO oxidation in (a) a 2 1 mixture of CO and 02 at atmospheric pressure, and (b) a 1 1 mixture of CO and 02 at atmospheric pressure. Symbols represent the activities of vanadates (solid squares), chromates (open squares), manganates (open triangles), ferrates (open circles), cobaltates (solid circles), and niquelates (solid triangles), plotted at the appropriate d-orbital occupation corresponding to the average valence of the B3+ ion. The activity is given either as (a) the reciprocal of the reaction temperature at which the activity is 1 [xmol of CO converted per m2 of catalyst per second or (b) as the rate of mole CO converted per unit area and unit time. With permission from Fierro...

An oxidizing reagent based on potassium ferrate(Vl) has been described [78], This potassium ferrate, when used in conjunction with an appropriate heterogeneous catalyst such as KIO montmorillonite clay, is a strong oxidant which produces cycloalkanols and cycloaUcanones from cycloalkanes, and benzyl alcohol and benzaldehyde from toluene. 

Gaertner reported an interesting recyclable iron catalyst system using imidazo-lium-derived ionic liquid 16 as the reaction medium. This liquid possesses a ferrate counteranion, which serves as a catalyst for cross-couplings between alkyl bromides and arylmagnesium bromides. As shown in Equation 5.32, the arylation of dodecyl bromide can be performed in this recyclable catalyst system, without losing significant activity even at a fifth cycle [39]. 

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