Rhenium preparation

Metallic rhenium prepared by this method is generally between 99.0 and 99.8 per cent pure. The chief impurity is potassium, probably as potassium hydroxide. The product is a dense gray-black powder. The yield is between 85 per cent and 95 per cent based upon the potassium per-rhenate used. 

Metallic rhenium, prepared by the reduction of either potassium perrhenate (see synthesis 60A) or ammonium perrhenate (see synthesis 60B), is placed in a previously ignited porcelain boat and inserted in a pyrex combustion tube of the type shown in Fig. 31. All air in the train is displaced with nitrogen that has been passed through alkaline pyrogallol A and sulfuric acid B. 

Some molybdenum contain from 0.002% to 0.2% rhenium. More than 150,000 troy ounces of rhenium are now being produced yearly in the United States. The total estimated Free World reserve of rhenium metal is 3500 tons. Rhenium metal is prepared by reducing ammonium perrhentate with hydrogen at elevated temperatures. 

Rhenium hexafluoride is readily prepared by the direct interaction of purified elemental fluorine over hydrogen-reduced, 300 mesh (ca 48 pm) rhenium powder at 120°C. The reaction is exothermic and temperature rises rapidly. Failure to control the temperature may result in the formation of rhenium heptafluoride. The latter could be reduced to rhenium hexafluoride by heating with rhenium metal at 400°C. 

Rhenium Halides and Halide Complexes. Rhenium reacts with chlorine at ca 600°C to produce rheniumpentachloride [39368-69-9], Re2Cl2Q, a volatile species that is dimeric via bridging hahde groups. Rhenium reacts with elemental bromine in a similar fashion, but the metal is unreactive toward iodine. The compounds ReCl, ReBr [36753-03-4], and Rel [59301-47-2] can be prepared by careful evaporation of a solution of HReO and HX. Substantiation in a modem laboratory would be desirable. Lower oxidation state hahdes (Re X ) are also prepared from the pentavalent or tetravalent compounds by thermal decomposition or chemical reduction. 

Compounds of the formulas Re(CR]), ReO(CH3)4, Li2[Re2(CH3)g] [60975-25-9], Re02(CH3)3 [56090-011-8], and Re03CH3 [70197-13-6] have been prepared. The first two compounds were obtained from reaction of rhenium hahdes or oxyhahdes and methyllithium the last three were formed from the species by oxidation or reduction reactions. The use of these hydride and alkyl complexes as catalysts is under investigation. 

The parent ligand forms complexes of the type [M(CO)5(HNSO)][AsF6] (M = Mn, Re) (Eq. 9.11). ° The rhenium complex can also be prepared by nucleophilic displacement of F from coordinated NSF using MesSnOH as the source of... 

Although these methods were applied for the synthesis of a number of various phthalocyanines with different central atoms (e.g., H2, Cu, Zn, Ni, Pt, Pd, Lu, etc.) not all metal phthalocyanines can be prepared by one of these methods. For example, the synthesis of silicon phthalocyanine, rhenium phthalocyanine and boron subphthalocyanine need more drastic conditions. In the following, an overview of the synthesis of phthalocyanines containing all central metals which have hitherto been inserted into the ring is given. 

Preparative Routes and Experimental Conditions for the Formation OF Rhenium Chalcogenide Halides... 

The addition, therefore, follows Markovnikov s rule. Primary alcohols give better results than secondary, and tertiary alcohols are very inactive. This is a convenient method for the preparation of tertiary ethers by the use of a suitable alkene such as Me2C=CH2. Alcohols add intramolecularly to alkenes to generate cyclic ethers, often bearing a hydroxyl unit as well. This addition can be promoted by a palladium catalyst, with migration of the double bond in the final product. Rhenium compounds also facilitate this cyclization reaction to form functionalized tetrahydrofurans. 

A catalyst supported on y-AFO was prepared from Re2Pt(CO)i2l (Fig. 70) and characterized by IR. X-ray photoelectron spectroscopy (XPS), and TPR. The chemi.sorbed cluster was treated with H2 at about 150 C resulting in fragmentation and formation of rhenium subcarbonyls at 400 C the sample was completely decarbonylated. A catalyst prepared from a mixture of Re3(//-H)3(CO)i2l and PtMe2(// -cod)] and treated under equivalent conditions showed the rhenium to... 

Non-ionic thiourea derivatives have been used as ligands for metal complexes [63,64] as well as anionic thioureas and, in both cases, coordination in metal clusters has also been described [65,66]. Examples of mononuclear complexes of simple alkyl- or aryl-substituted thiourea monoanions, containing N,S-chelating ligands (Scheme 11), have been reported for rhodium(III) [67,68], iridium and many other transition metals, such as chromium(III), technetium(III), rhenium(V), aluminium, ruthenium, osmium, platinum [69] and palladium [70]. Many complexes with N,S-chelating monothioureas were prepared with two triphenylphosphines as substituents. 

Fig. 6 displays the X-ray powder diffraction patterns of rhenium oxide. While the as-prepared sample is amorphous to X-ray, the sample soaked in acetone and dried at 100"C clearly exhibits sharp reflections corresponding to Re03. The large difference between the two X-ray patterns suggests that the processing conditions play a key role in the crystallinity and surface characteristics. As shown in the TGA plot of the as-prepared sample (Fig. 7), the weight loss of about 10% below 100 C results from the loss of water. 

Pt-Re-alumina catalysts were prepared, using alumina containing potassium to eliminate the support acidity, in order to carry out alkane dehydrocyclization studies that paralleled earlier work with nonacidic Pt-alumina catalysts. The potassium containing Pt-Re catalyst was much less active than a similar Pt catalyst. It was speculated that the alkali metal formed salts of rhenic acid to produce a catalyst that was more difficult to reduce. However, the present ESCA results indicate that the poisoning effect of alkali in Pt-Re catalysts is not primarily due to an alteration in the rhenium reduction characteristics. 

Binary rhenium dithiocarbamato complexes are prepared with the metal in the oxidation state -I- 3, + 4 and + 5. 

Finally, (7 5-heterolyl)Mn(CO)3 complexes, the heterocymantrenes, have been prepared for the complete family of group 15 elements from N to Bi. As shown in Scheme 10, 2,5-dimethylarsacymantrene (71) is obtained directly from l-phenyl-2,5-dimethylarsole (25) in 50% yield by heating with Mn2(CO)10.26 The tetraphenylarsacymantrene (74) is obtained by pyrolysis of the corresponding cr-complex 72. Rhenium complex 75 is obtained by an analogous reaction. The 2,5-dimethylstibacymantrene (76)8 and 2,5-dimethylbismacymantrene (78)27 were obtained by similar routes. 

Another type of ligand is the monoanionic, tridentate oxygen donor [(C5H4R)Co-(P(0)R R")3] (Lor), which has been used to prepare the complexes of technetium [37] and rhenium [38] [M03L] and [MOX2L] (X Cl, Br). These complexes are stable in organic solvents but hydrolyse slowly in water. In order to evaluate their usefulness in radioimmunotherapy, the corresponding compounds were also prepared with radioactive rhenium isotopes. 

To transfer the original synthesis to technetium was not very convenient, as it would have to start from TcBr(CO)5 (32a). A preparation has recently been reported which starts from 3a or 19a in refluxing THF and used BH3 as the reducing agent [36]. The complex 31a could be isolated in 60-70% yield, based on Tc, and has been characterized by i.r. specroseopic methods as well as Tc and Cl analysis, and compared to its rhenium congener (Scheme 5). 

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