Rhenium, and Technetium

The kinetics of the oxidations of trans-[Tc(dppe)X2] (X = Cl , Br ) by Co(III) amine complexes have been investigated in pure and mixed DMF and CH3CN solvent systems, with an observed increase in the rate constant with DMF concentrations. The rate constants for the reductions of three metal carbonyl dimers [M2,M = Mn(CO)5, CpMo(CO)3, and Co(CO)4] by [Re(CO)5r in THF (measured using infrared stopped-flow spectroscopy) do not parallel the reduction 

Introduction—The organometallic chemistry of technetium and rhenium has been the subject of three reviews. Interesting new developments in the chemistry of these elements reported this year include the first preparation and characterization of ReOCl2 which, compared with the other oxochlorides of rhenium, is relatively stable with respect to reaction with air or water, it is however markedly thermally unstable. Re03l has been observed by mass spectrometry in the vapour from a mixture containing Re03 and 

The preparation of the novel p-hydrido-derivatives HMRe(CO)io (M = Cr, Mo, or W) has been achieved and the structure of the chromium compound (42) determined by X-ray crystallography. The hydridopolynuclear carbonyl 

Carbonyl Complexes.—As indicated for chromium only a selection of this material is reported. 

HCrRe(CO)io, HRe3(CO)i4, and Cr(CO)6 by stirring in an n-pentane slurry over 85 % H3PO4 for two days. The first of these products has been separated by fractional sublimation and shown to contain molecules with a p-hydrido-group linking the two M(CO)j centres (42). Other members of this series of compounds HM M (CO)io (M = Mn or Re = Cr, Mo, or W) have been prepared in a similar manner.  

Re(CO)5F,ReF5 and [Re(CO)6][Re2Fu] have been obtained from ReF and Re2(CO)io in anhydrous HF. Both compounds are very sensitive to moisture and their structures have been confirmed by AT-ray crystallography. The former (91) contains essentially octahedral Re(CO)sF and ReFg units 

Introduction.—The organometallic chemistry of technetium and rhenium reported during 1974 has been surveyed. The ligand-induced redox reactions of rhenium halides have been reviewed, and the chemistry of cyanide complexes of Group Vila metals has received attention. The electrochemistry of technetium and rhenium has been the subject of two reviews, and a general monograph on the production, uses, and disposal of technetium has appeared. Recently published crystal structures of complexes of technetium and rhenium have been collated.  

Inorganic Molecules.— The crystal structure of the technetium(vii) oxide, Tca07, comprises discrete molecular units. The oxygen atoms form a tetrahedron around each metal atom, and two such tetrahedra are linked through a linear Tc-O-Tc system to form a dinuclear, centrosymmetric molecule. The Tc-O(bridging) and the average Tc-O(terminal) distances are 1.840(1) and 1.672 A, respectively. 

I gure 4 Molecular structure of the cor oimd [ReaOjfSxCNEtj),] (Reproduced by permission from Inorg. Nuclear Chem. Letters, 1971,7,523) 

In the octahedral complex [Re Cl(Nj)(PMe2Ph)J, the chlorine and the unidentate dinitrogen ligands are trans to each other and partially disordered. The Re-Cl, Re-N, N-N, and average Re-P distances are 2.521(4), 1.97(2), 1.06(3), and 2.42(1) A, respectively. The dinitrogen ligand coordination is linear, with a Re-N-N angle of 177(1)°. 

and aroyl halides all react with [ReCl(N2)(PMe2Ph)4]. However, protonation occurs at the metal to give the hydride [ReClH(N2)-(PMe2Ph)4], whereas slow acylation and aroylation occur at the end nitrogen atom. Interestingly, this latter reaction is the reverse of the preparation of the rhenium dinitrogen complexes. Alkyl halides do not react with rhenium complexes of dinitrogen. 

Interesting new developments in the chemistry of these elements include the 

ReOMe4 has been prepared by the reaction of [ReOCl3(PPh3)2] or ReOCl4 with LiMe in Et20 at — 35 °C. Spectral data are consistent with this d1 metal alkyl possessing a square-pyramidal C4 structure.617 

Carbonyl Complexes.—For a comprehensive discussion of this topic the reader should consult the Organometallic Specialist Periodical Report. 

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Polynuclear Carbonyls. Several stmctures consist of dinuclear metal carbonyls as shown in stmctures (4)—(6). The metal atoms in Mn2(CO) Q, as also for technetium and rhenium, are held together by a metal—metal bond and the compound contains 10 terminal CO ligands, five coordinated to each atom. The CO ligands of Mn2(00) 0 adopt a staggered configuration as illustrated in stmcture... 

E° for some manganese, technetium and rhenium couples in acid solution at 25°C... 

Table 24.3 Oxidation states and stereochemistries of manganese, technetium and rhenium...

Manganese, Technetium and Rhenium Table 24.6 Oxohalides of Group 7... 

Bearing this situation in mind we wished to describe the present status of studies on chemistry and its applications of technetium and rhenium. A part of this book was planned before the "Topical Symposium on the Behavior and Utilization of Technetium 93" was held in Sendai, Japan in March 1993, but the planning of the book in this style was accelerated after the symposium by suggestions from our friends. The editors are grateful for the cooperation from the contributes and the publisher. 

Nicolini M, Bandoli G, Mazzi U (eds) (1990) Technetium and rhenium in chemistry and nuclear medicine 3, Cortina International, Verona/Raven, New York... 

Schiff bases provide useful mixed donor sets. The carbonyl function of the most frequently used ligands is derived from either 1,3-dicarbonyl compounds or salicylaldehyde. Favourable combinations involve O-, N- and S-donor atoms. A range of technetium and rhenium complexes exist with bi-, tri-, tetra- and pentadentate ligands. The geometry of these complexes depends on the number and type of coordinating atoms as well as on the chain length between the donor atoms in the SchifF-base ligands. 

Edwards DS, Cheesman EH, Watson MW, Maheu LJ, Nguyen SA, Dimitre L, Nason T, Watson AD, Walovitch R (1990) In Nicolini M, Bandoli G, Mazzi U (eds) Technetium and rhenium in chemistry and nuclear medicine 3, Cortina International, Verona, Raven Press, New York, p 433... 

Archer CM, Edwards B, Kelly JD, King AC, Burke JF, Riley ALM (1994) Technetium labelled agents for imaging tissue hypoxia in vivo, 4th International Symposium on Technetium and Rhenium in Chemistry and Nuclear Medicine, Bressanone, Italy, September 12-14... 

High- and Low-Valency Organometallic Compounds of Technetium and Rhenium... 

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