Iron sulfoxide complexes

The use of palladium(II) sulfoxide complexes as catalyst precursors for polymerization has met with mixed results thus a report of a palla-dium(II) chloride-dimethyl sulfoxide system as a catalyst precursor for phenylacetylene polymerization suggests similar results to those obtained using tin chloride as catalyst precursor (421). However, addition of dimethyl sulfoxide to solutions of [NH fPdCh] decreases the activity as a catalyst precursor for the polymerization of butadiene (100). Dimethyl sulfoxide complexes of iron have also been mentioned as catalyst precursors for styrene polymerization (141). 

No sulfoxide complexes of osmium have been reported. Unsymmetri-cal dialkyl sulfoxides have been utilized in extraction studies, and methyl-4,8-dimethylnonyl sulfoxide has found application in the extraction of iron (266). Extraction of ruthenium from hydrochloric acid solutions by sulfoxides has been studied (470) and comparisons of sul-fones, sulfoxides, and thioethers as extractants for nitrosoruthenium species reported (441, 443). Similar studies on the extraction of nitro-soosmium species have been reported (442). 

A values have been obtained for oxidation of benzenediols by [Fe(bipy)(CN)4], including the effect of pH, i.e., of protonation of the iron(III) complex, and the kinetics of [Fe(phen)(CN)4] oxidation of catechol and of 4-butylcatechol reported. Redox potentials of [Fe(bipy)2(CFQ7] and of [Fe(bipy)(CN)4] are available. The self-exchange rate constant for [Fe(phen)2(CN)2] has been estimated from kinetic data for electron transfer reactions involving, inter alios, catechol and hydroquinone as 2.8 2.5 x 10 dm moF s (in dimethyl sulfoxide). 

Phthalocyaninato(2-)] iron(II) is a dark blue, thermally stable solid that can be sublimed in vacuo at 300°. It is very soluble in pyridine, giving deep blue solutions of the bis(pyridine) adducts. It also forms an unstable purple hexaaniline adduct when dissolved in aniline. It is soluble in concentrated sulfuric add and dimethyl sulfoxide (slightly) but is insoluble in most other organic solvents. The iron(II) complex, unlike the corresponding iron(II) porphines, is relatively stable toward oxidation to the iron (III) state. The electronic spectrum shows the following absorption bands (1-chloronaphthalene solution) 595 (e = 16,000), 630 (e = 17,000), 658 (e = 63,000) (pyridine solution) 333 (e = 45,000), 415 (e = 15,000), 395 (e = 2000), 658 nm (e = 8000). 

Also, coordination compounds and metal carbonyls are able to undergo a PET, resulting in initiating radicals [63]. Recently investigated examples are iron chloride based ammonium salts [149], vanadium(V) organo-metallic complexes [150], and metal sulfoxide complexes [151]. However, the polymerization efficiency of some systems is only low due to redox reactions between the central metal ion and the growing polymer radical, and the low quantum yields of PET. 

The above discussion has concentrated upon the reagents used, but it is equally of value to comment on the substrate, particularly in reactions for which other oxidation methods have been reported to fail. A good example is the oxidation of the iron-carbonyl complex (31) to the ketone (32 equation 14). The use of dimethyl sulfoxide activated with sulfur trioxide-pyridine complex gave a 70% yield of the product, in contrast to the use of the Pfitzner-Moffatt procedure (dimethyl sulfoxide-DCC) or the chromium... 

Macrocyclic sulfoxides and sulfones have begun to attract interest as phase transfer catalysts <81H(16)1701, 86JCS(Pi)465> they are best obtained by oxidation of the parent crown thioether. By way of illustration, mono(sulfoxide) of 9S3 has been isolated as an iron(II) complex (Section 9.30.3.4), while the tris(sulfone) can be prepared from 9S3 with excess permanganate <871C3762>. Cyclic sulfones extrude SO2 at 500°C (60-80 Pa) to give cyclophanes <89JOC2632,90CC1066>. 

The resolution of a racemic iron acetyl complex was achieved by Davies and Becker by its transformation into a 1 1 mixture of diastereoisomeric sulfides (67a) and (67b) [158]. Oxidation by mCPBA operates selectively on one diastereoisomer (because of a suitably located hydroxy group). The sulfoxide (68) was easily separated from sulfide (67b) and desulfurized to give the desired target. This a case of kinetic resolution of an equimolar mixture of diastereoisomers. 

Chiral iron acyl complexes have been applied to the asymmetric synthesis of cyclopropane carboxylic acids, sulfoxides and p-amino acids. Further details and applications may be found in the reviews given in the reference... 

The N2S4 macrocycle (50) forms a deep blue low-spin iron(II) complex, characterized by X-ray diffraction. One hopes that kinetic studies will follow. Kinetic studies of N4 macrocycle complexes [Fe(N4)LL ]" appear regularly, usually involving replacement of one or both of L, L. Reaction of phthalocyaninatoiron(II) with imidazole, in dimethyl sulfoxide solution, proceeds by consecutive first-order processes, the second some thousand times slower than the first. The N4 macrocycles (51) link this section with the previous section kinetics of reactions of [Fe(51)(MeCN)]2 with such ligands as 1-methylimidazole, pyridine, tributyl phosphite, tributyl phosphine, and carbon monoxide have been investigated. A series of complexes [Fe(51)L2], this time only for (51) with R = Me, has been studied with a... 

Complexes of butyl vinyl sulfoxide and iron, chromium and cobalt (III) nitrates were found to be unstable, the ferric salt (the least stable) exploding even as a 40 mol% solution in benzene. It is considered that other vinyl sulfoxide ligands will behave similarly. 

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