Diiodide

Submitted by JOHN D. CORBETT Checked by ARNDT SIMONt 

Samples of Lal2 equilibrated for weeks near 850° with a large excess of metal, preferably with high surface area, have been found to contain also the cluster phase La(La7Ii2)4 (isostructural with Sc7Cli2s). The phase relationships of this with the other phases are not known, but the yield is negligible when the excess metal has limited surface area. 

The blue-black lanthanum diiodide is a very good reducing agent and should be stored and handled in the absence of 02, H20, etc. It is one of the better char- 

The structure of Lal2 and of the isostructural Cel2 and Prl2 is of the MoSi2 (or CuTi2) type and gives an almost alloy-like impression with its square layers. For Lalj the lattice constants are a = 3.922, c = 13.97 A, space group mm, d = 5.46 g/cm.  

Inorganic Syntheses, Volume 22 Edited by Smith L. Holt, Jr. Copyright 1983 by Inorganic Syntheses, Inc. 

The synthesis involves the direct reaction of Lala with a modest excess of La. A Ta (Nb or Mo) container is essential (sec J. D. Corbett, Inorg. Synth., 22,15 (1983)) and sublimed Lala is preferable. An open crucible can be used under a noble-gas atmosphere with only a small amount of sublimation of Lala during the reaction (and accompanying reaction with the silica walls), but a sealed container gives better control of stoichiometry and purity. Lanthanum metal is somewhat reactive toward air and the best product is obtained by minimizing atmospheric exposure of the lanthanum metal used in the reduction. 

The Lala (5-2S g) and somewhat more than the stoichiometric amount of Lat (13.46% of Lala by weight) are weighed in the dry box and transferred into the crucible. If an open crucible is used, this is placed in the closed end of a fused-silica tube long enough so that the upper end, which is equipped with a standard taper joint, will extend 10-15 cm from the (vertical) furnace. This end is capped with a Pyrex top equipped with a standard taper joint and stopcocks to allow evacuation and introduction of a noble gas. The joint 

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The majority of preparative methods which have been used for obtaining cyclopropane derivatives involve carbene addition to an olefmic bond, if acetylenes are used in the reaction, cyclopropenes are obtained. Heteroatom-substituted or vinyl cydopropanes come from alkenyl bromides or enol acetates (A. de Meijere, 1979 E. J. Corey, 1975 B E. Wenkert, 1970 A). The carbenes needed for cyclopropane syntheses can be obtained in situ by a-elimination of hydrogen halides with strong bases (R. Kdstcr, 1971 E.J. Corey, 1975 B), by copper catalyzed decomposition of diazo compounds (E. Wenkert, 1970 A S.D. Burke, 1979 N.J. Turro, 1966), or by reductive elimination of iodine from gem-diiodides (J. Nishimura, 1969 D. Wen-disch, 1971 J.M. Denis, 1972 H.E. Simmons, 1973 C. Girard, 1974),... 

In the reaction of Q,/3-unsaturated ketones and esters, sometimes simple Michael-type addition (insertion and hydrogenolysis, or hydroarylation, and hydroalkenylation) of alkenes is observed[53,54]. For example, a simple addition product 56 to methyl vinyl ketone was obtained by the reaction of the heteroaromatic iodide 55[S5]. The corresponding bromide affords the usual insertion-elimination product. Saturated ketones are obtained cleanly by hydroarylation of o,/3l-unsaturated ketones with aryl halides in the presence of sodium formate, which hydrogenolyses the R—Pd—I intermediate to R— Pd—H[56]. Intramolecular hydroarylation is a useful reaction. The diiodide 57 reacts smoothly with sodium formate to give a model compound for the afla-toxin 58. (see Section 1.1.6)[57]. Use of triethylammonium formate and BU4NCI gives better results. 

When the pyrolysis gases are quenched with a molar excess of iodine vapor, a yield of greater than 50% -xylylene diiodide is recovered. The observation of this effect offered the first direct chemical support for the idea that DPX pyrolysis results in PX (1) (3). 

Lead Iodide. Lead diiodide, Pbl2, forms a powder of yellow hexagonal crystals some physical properties are given in Table 1. Lead diiodide is soluble in alkaUes and potassium iodide, and insoluble in alcohol. It is made by treating a water-soluble lead compound with hydroiodic acid or a soluble metal iodide. It is readily purified by recrystaUization in water. 

Titanium Dhodide. Titanium diiodide is a black soHd p = 499(0) kg/m ) that has the cadmium iodide stmcture. Titaniums occupy octahedral sites in hexagonaHy close-packed iodine layers, where a = 411 pm and c = 682 pm (144). Magnetic studies indicate extensive Ti—Ti bonding. Til2 reacts rapidly with water to form a solution of titanous iodide, Til. ... 

Titanium diiodide may be prepared by direct combination of the elements, the reaction mixture being heated to 440°C to remove the tri- and tetraiodides (145). It can also be made by either reaction of soHd potassium iodide with titanium tetrachloride or reduction of Til with silver or mercury. 

Titanium Triiodlde. Titanium triiodide is a violet crystalline soHd having a hexagonal unit cell (146). The crystals oxidize rapidly in air but are stable under vacuum up to 300°C above that temperature, disproportionation to the diiodide and tetraiodide begins (147). 

Also formed by the direct combination of the elements is a red soHd compound, arsenic diiodide [13453-17-3] AS2I4 or ASI2, which melts at 130°C and dissolves in organic solvents. Treatment of this compound with water causes disproportionation. 

Formation of the /3-lactam (161) by reaction of the dianion (160) with methylene diiodide provides an example of a [3 + 1] type of ring closure (79TL2031). The insertion of carbon... 

Diiodomethane (methylene diiodide) [75-11-6] M 267.8, m 6.1 , b 66-70 / l-12mm, d 3.325. Fractionally distd under reduced pressure, then fractionally crystd by partial freezing, and stabilized... 

Compound 9 has been prepared by the latter authors using triethylene glycol diiodide and triethylene glycol diamine (see Eq. 4.11) and an alkali metal carbonate in acetonitrile solution. ... 

Polyfunctional fluoronitro alcohois are provided by tlie SRNl reaction of a perfluoroalkyl iodide or alkylene diiodides with the anhydrous lithium salt of 2-nitropropane l,3-diol acetonide. Hydrolysis of the resulting perfluoroalkyl-... 

Fluorine addition to alkenes is a violent reaction, difficult to control, and accompanied by substitution of hydrogens by fluorine. Vicinal diiodides, on the other hand, tend to lose I2 and revert to alkenes, making them an infrequently encountered class of compounds. 

Nal, SiCl4, rt, 20-60 min, 78% yield. Cleavage results in subsequent formation of a diiodide, but this is not a general process. For the most part, ketals are cleaved to give the ketone, while catechol methylene acetals return the catechol. ... 

Of the anhydrous dihalides of iron the iodide is easily prepared from the elements but the others are best obtained by passing HX over heated iron. The white (or pale-green) difluoride has the rutile structure the pale-yellow dichloride the CdCl2 structure (based on cep anions, p. 1212) and the yellow-green dibromide and grey diiodide the Cdl2 structure (based on hep anions, p. 1212), in all of which the metal occupies octahedral sites. All these iron dihalides dissolve in water and form crystalline hydrates which may alternatively be obtained by dissolving metallic iron in the aqueous acid. 

The isomorphous diiodides of Ce, Pr and Gd stand apart from all the other, salt-like, dihalides. These three, like LaH, are notable for their metallic lustre and very high conductivities and are best formulated as (Ln ,2I",e", the electron being in a delocalized conduction band. Besides the dihalides, other reduced species have been obtained such as LnsCln (Ln = Sm, Gd, Ho). They have fluorite-related structures (p. 118) in which the anionic sublattice is partially rearranged to accommodate additional anions. 

Dimethyl-1,2,4-triazolium iodide with palladium acetate yields the carbene adduct 182 (97JOM(530)259). Under water it undergoes cis-trans isomerization to 183. Some other derivatives were reported in 1981 (81BCSJ800). 1,1 -Methylenebis(4-alkyl-l,2,4-triazolium)diiodides (alkyl = /-Pr, n-Bu, octyl) with palladium(II) acetate give the mononuclear complexes [L Pdl ] (99EJIC1965), where L2= l,l -methylenebis(4-R-l,2,4-triazol-2-ylidene) (R = /-Pr, n-Bu, octyl). Thermolysis of the products in THF gives the rran -dinuclear complexes 184... 

R = /-Pr, n-Bu, octyl). The reaction of l,r-methylenebis(4-methyl-l,2, 4-tria2olium)diiodide with palladium(II) acetate however proceeds differently and gives the cationic dicarbene [L2Pd(02CMe)]I. 

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