Jeffrey C. Bryan

Tungsten complexes with strong π-donor and π-acceptor ligands: W(E)Cl2(L)(PR3)2 (E = O, NR, S, and L = CO, CNR, CH2CHR and OCHMe)

Abstract The synthesis and characterization of a series of tungsten complexes, W(E)Cl2(L)(PR3)2, containing both a π-donor group (E = oxo, imido, or sulphido) and a π-acceptor ligand (L = CO, CNtBu, CH2CHR, OCHMe) is reported (PR3 = PMe3, PMePh2). The compounds are prepared by substitution of a phosphine ligand in W(E)Cl2(PR3)3 by L and by oxidative addition of heterocumulenes EL, epoxides or episulphides to WCl2(PMePh2)4. All of the compounds have an octahedral structure with the π-donor and π-acceptor ligands cis, according to spectroscopic data and X-ray crystal structures of oxo-carbonyl (4), oxo-ethylene (7) and imido-carbonyl (25) complexes. The ethylene ligands are oriented perpendicular to the tungsten-oxygen, -nitrogen, or -sulphur multiple bond, and are non-fluxional by NMR. These geometrical features are a direct result of the electronic structure of the d2 metal centre. The dihapto coordination of acetaldehyde shows the substantial π-basicity of the tungsten(IV)-oxo centre. The CO stretching frequencies indicate that the donor abilities are in the order: oxo

Dideoxygenated calix[4]arene crown-6 ethers enhanced selectivity for caesium over potassium and rubidium

Calix[4]arene crown-6 ethers derived from dideoxygenated calix[4]arene exhibit enhanced extraction selectivity for caesium over potassium; the crystal stucture of the uncomplexed calix[4]arene monobenzocrown-6 ether exists in the 1,3-alt conformation in the solid state.

RADIOPHARMACEUTICAL DESIGN USING NOVEL RE-188 IMIDO COMPLEXES

Several efficient new methods for synthesizing rhenium compounds containing a multiply bonded imido linkage (Re=N-R) between the metal and organic compounds for radiopharmaceutical applications are reported. The imido linkage is stable and compatible with typical organic functional groups, and offers distinct structural and synthetic advantages over other types of linkages commonly used in radiopharmaceutical design. Syntheses of representative peptide and steroid compounds from hydrazine and phosphinimine imido precursors are described, and the preparation of a Re-imido complex is discussed. A promising new Re-radiolabeling strategy for directly synthesizing rhenium imido radiopharmaceuticals, targeted for low-capacity receptor sites relevant for cancer therapy and based on solid supported imido precursors, is presented.

Dual-Host Combinations: Using Tripodal Amides to Enhance Cesium Nitrate Extraction by Crown Ethers

Extraction of alkali metal salts by designed cation hosts, such as crown ethers 1 and calixarenes,2 has been widely investigated in recent years, as driven, to an extent, by the importance of separations of certain cationic contaminants such as Cs+ and Sr2+ in nuclear-fuel reprocessing and waste remediation. 3 New cation hosts used as extractants for these and other metals have reached impressive levels of selectivity for such demanding “needle-in-the-haystack” applications. The success of neutral cation hosts used in ion-pair extraction systems stems in part from the practical advantage of stripping extracted salts with water, resulting in processes that yield a pure salt product stream with little secondary waste. Examples of such practical ion-pair extraction applications include processes for nuclear-waste treatment that produce aqueous streams of relatively pure cesium nitrate2h or sodium pertechnetate,4 suitable for vitrification and geologic disposal. These processes employ calix-crown and crown ether extractants, such as those shown in Figure 1 for cesium. Although ion-pair extraction involves anion co-extraction, ligand design has focused primarily on the design of the cation host, typically with little or no attention to accommodating the anion.

Ion Recognition Approach to Volume Reduction of Alkaline Tank Waste by Separation and Recycle of Sodium Hydroxide and Sodium Nitrate

This research has focused on new liquid-liquid extraction chemistry applicable to separation of major sodium salts from alkaline tank waste. It was the overall goal to provide the scientific foundation upon which the feasibility of liquid-liquid extraction chemistry for bulk reduction of the volume of tank waste can be evaluated. Sodium hydroxide represented the initial test case and primary focus. It is a primary component of the waste1 and has the most value for recycle. A full explanation of the relevance of this research to USDOE Environmental Management needs will be given in the Relevance, Impact, and Technology Transfer section below. It should be noted that this effort was predicated on the need for sodium removal primarily from low-activity waste, whereas evolving needs have shifted attention to volume reduction of the high-activity waste. The results of the research to date apply to both applications, though treatment of high-activity wastes raises new questions that will be addressed in the renewal period. Toward understanding the extractive chemistry of sodium hydroxide and other sodium salts, it was the intent to identify candidate extractants and determine their applicable basic properties regarding selectivity, efficiency, speciation, and structure. A hierarchical strategy was to be employed in which the type of liquid-liquid-extraction system varied in sophistication from simple, single-component solvents to solvents containing designer host molecules. As an aid in directing this investigation toward addressing the fundamental questions having the most value, a conceptualization of an ideal process was advanced. Accordingly, achieving adequate selectivity for sodium hydroxide represented a primary goal, but this result is worthwhile for waste applications only if certain conditions are met.