Complexes of manganese, technetium and rhenium

Oxidation of the decacarbonyldimetal(O) compounds of manganese, technetium, and rhenium by halogens gives the corresponding halopentacarbonyhnetal(I) complexes (see equation 34). 

Tetrahedral [Mn(NCSe)4] and octahedral [Mn(NCSe)g] anions are known (162, 295, 6i7, 655, 656), and [Re2(NCSe)8] has been tentatively identified (377). There seem to be no reports of similar Tc compounds, nor indeed of any mixed-ligand selenocyanate complexes of either technetium or rhenium. Some mixed-ligand complexes of manganese(II) selenocyanate have been prepared, and in every case so far described the selenocyanate is N-bonded. Analogous to the thio-... 

Many compounds of technetium and rhenium are of analogous composition and of corresponding physical and chemical properties. Because of the very similar ionic radii, isotypic crystal structure formation of analogous compounds could often be observed. Technetium remarkably differs from manganese by the high stability of pertechnetate compared with permanganate. Moreover, divalent technetium does not exist as a hydrated ion but only as a stabilized complex. 

The synthesis of pentacarbonyl rhenium(I) halides, Re(CO)5X, succeeded from simple and complex rhenium halides below 200 atm of CO at 200° C. The compounds are extraordinarily stable and form easily, often quantitatively, from carbon monoxide and rhenium metal in the presence of other heavy metal halides or halogen sources such as CC14. Later we prepared the corresponding carbonyl halides of manganese (67) and technetium (68) from their respective carbonyls. It was found that the corresponding binuclear tetracarbonyl halides [M(CO)4X]2 (M = Mn, Re) could be made by heating the mononuclear M(CO)5X complexes (15, 69), as well as by other methods. 

Under the influence of water, cationic manganese compounds decompose immediately, as in organic donor solvents such as acetone and tetrahydrofuran. In contrast to isoelectronic compounds of the chromium group, diolefin technetium and rhenium complexes have cis structures. In aqueous solution, the cation [Re(CO)4 ( 2114)2] is stable the Re —C2H4 bond in [Re(CO)5 ( 2114)] is also stable. There is no exchange between free ethylene and the ethylene in the complex. 

The chemistry of technetium(II) and rhenium(II) is meagre and mainly confined to arsine and phosphine complexes. The best known of these are [MCl2(diars)2], obtained by reduction with hypophosphite and Sn respectively from the corresponding Tc and Re complexes, and in which the low oxidation state is presumably stabilized by n donation to the ligands. This oxidation state, however, is really best typified by manganese for which it is the most thoroughly studied and, in aqueous solution, by far the most... 

This facile approach to the carbene chemistry of rhenium has not yet been investigated with technetium. Further reactions with the technetium cluster 44a have been performed in C6H6/HC1 to yield the compound [( 6H6)Tc(CO)3]+ (66) which previously had only been described for manganese and rhenium [81]. "Tc-NMR of the latter compound exhibits a resonance at -1983 ppm (relative to [Tc04]- ), and it therefore fits very well into the range proposed for Tc(I) complexes. 

These metals form chalcogenolate complexes in several oxidation states, and from the application-oriented point of view manganese compounds have been synthesized as models for hydrodesulfurization processes and rhenium and technetium derivatives as models for radiopharmaceuticals. 

Only one compound of technetium, an oxide, has been investigated during the period covered by this Report. Interest in manganese and rhenium has been focused mainly on various halide, oxo-, and carbonyl complexes. 

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