Iron allenes

As is the case with assessments of the toxicity of dissolved trace metals, the development of sediment quality criteria (SQC) must be based on the fraction of sediment-associated metal that is bioavailable. Bulk sediments consist of a variety of phases including sediment solids in the silt and clay size fractions, and sediment pore water. Swartz et al. (1985) demonstrated that the bioavailable fraction of cadmium in sediments is correlated with interstitial water cadmium concentrations. More recent work (e.g., Di Toro et al, 1990 Allen et al., 1993 Hansen et al, 1996 Ankley et ai, 1996, and references therein) has demonstrated that the interstitial water concentrations of a suite of trace metals is regulated by an extractable fraction of iron sulfides. 

Immunohistochemical studies carried out in our laboratories have demonstrated the presence of xanthine oxidase in synovial endothelial cells (Stevens etal., 1991). As expected, the activity of this enzyme per unit weight of tissue is generally higher in synovia taken from RA patients due to their increased vascularity (Allen et al., 1987). In addition, it has also been shown that rheumatoid synoviocytes contain increased levels of iron-saturated ferritin (Morris et d., 1986). Xanthine oxidase (but not dehydrogenase) is able to mobilize iron from ferritin, supplying the necessary transition metal catalyst for the Haber-Weiss reaction and promoting OH formation (Biemond eta/., 1986). 

A carbon-iron bond is also formed by the reaction of the cyclopropenium salt 185 with dicarbonyl(i/5-cyclopentadienyl)(trimethylsilyl)iron [92], (Scheme 69) In the reaction with benzocyclobutenylidene- 5-cyclopentadienyliron(II) hexafluorophosphate 186, CpFe(CO)2R (R=cyelo-C3H5, CH2-cyclo-C3H5) is converted to the allene and butadiene complexes, 187 and 188, respectively [93]. (Scheme 70)... 

An example of an iron-catalyzed C-C bond formation reaction was reported in 2001 [89]. Treatment of propargyl sulfides 87 with trimethylsilyldiazomethane in the presence of 5 mol% FeCl2(dppb) gave substituted homoallenylsilanes 88 in good to moderate yields (Scheme 3.43). The silanes 88d and 88e, which bear two centers of chirality, were obtained as 1 1 mixtures of diastereomers. Slight diastereoselectivity (2 1) was seen for the formation 88f, which is an axially chiral allene with a sterogenic center. 

An intriguing approach to nitrogen-substituted allenes such as 253 was reported by van Vranken and co-workers (Scheme 8.67) [148]. Iron(II)-catalyzed sulfimidation of propargyl sulfides 252 and subsequent [2,3]-sigmatropic rearrangement furnish 253 in moderate to good yields. 

Several stoichiometric methods for transition metal-promoted transformations of allenes have been studied, involving metals such as iron [77] and titanium [78, 79]. The titanium-mediated reactions developed by Sato and co-workers have probably the greatest synthetic impact, as exemplified by the conversion of silylated allene 150 to 1,4-diene 152 (Scheme 14.38) [78],... 

It should be pointed out that the treatment of phosphorus or sulfur donors bearing ferrocenyl groups with diiodine results in the formation of molecular charge-transfer adducts without simultaneous oxidation of the ferrocenyl groups (Durfey et al. 2000, Gridunova et al. 1982). At the same time, the reaction of 4-ferrocenyl-l,3-dithiolene-2-thione with diiodine leads to a charge-transfer complex in which the iron has been oxidized from Fe" to Fe ". This was confirmed by magnetic measurements and Moessbauer spectroscopy (Allen et al. 2003). 

Complexes M(CH2C CC=CMe)(CO)nCp [325 M = Mo, n = 3 M = Fe, = 2 (Scheme 74)] were obtained from the carbonyl anions and l-chlorohexa-2,4-diyne. Subsequent chemistry involves protonation (HBF4) to cationic allene or diene complexes, or addition of MeOH to give allylic derivatives, which are formed with concomitant insertion of CO. The latter can also be obtained from the cationic species and NaOMe. The allene-iron cation reacts with NHEt2 to form an ynenyl complex. The luminescent complex Re(CO)3(5,5 -Bu 2-bpy) 2 (At-C=CC6H4C CC=CC6H4C=C) has been reported. ... 

G. (1999) Structural chemistry of uranium associated with Si, Al, Fe gels in a granitic uranium mine. Chem. Geol. 158 81-103 Allen, G.C. Kirby, C. Sellers, R.M. (1988) The effect of the low-oxidation-state metal ion reagent tris-picolinatovanadium(II) formate on the surface morphology and composition of crystalline iron oxides. J. Chem. Soc. Faraday Trans. I. 84 355-364... 

Allen, M. and Whitfield, A.B. (1964) Rapid methods for the routine determination of major nutrient elements and iron and manganese in the leaves of fruit trees. Annual Report of the East Mailing Research Station, pp. 143-147. 

Seligman, P. A., Caskey, J. H., Prazier, J. L., Zucker, P. M., Podell, E. R., and Allen, R. H. (1983). Measurements of iron absorption from prenatal multivitamin-mineral supplements. Obstet. Gynecol. 61, 356-362. 

Glikson A. and Allen C. (2004) Iridium anomalies and fractionated siderophile element patterns in impact ejecta, Brockman Iron Formation, Hamersley Basin, Western Australia evidence for a major asteroid impact in simatic crustal regions of the early pro-terozoic Earth. Earth Planet. Sci. Lett. 220, 247-264. 

In 1976, Pasto and coworkers described the Sn2 reaction of primary and secondary alkyl Grignard reagents with terminal and non-terminal propargyhc chlorides (Scheme 48). Only 0.1% iron(III) chloride is necessary to obtain various allenes in good yields. 

These last years, several syntheses of natural products using an iron-catalyzed reaction of Grignard reagents have been published. In 1969, Meinwald and Hendry used the reaction discovered by Kharasch and Tawney to prepare an allenic sesquiterpenoid isolated from the grasshopper Romalea Microptera (Scheme 61). 

Flint, D. H., and R. M. Allen, Iron-sulfur proteins with nonredox functions , Chem. Rev., 96, 2315-2334 (1996). 

For example, Allen et al. have recently isolated an iron carbonyl complex with a bicarbonate counterion (Fe(dmpe)2(C0)H)(HC03) with dmpe = 1,2 bis(dimethylphosphino)ethane, resulting from the iron(II)-mediated reductive disproportionation of C02 [104], although the reaction mechanism is still speculative. In a related system, Karsh et al. [9] had observed, during the reaction of C02 with Fe(PMe3)4, the formation of a side-on complex Fe(C02)(PMe3)4 and of a carbonyl carbonate species Fe(PMe3)3(C0)(C03). 

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