Complexes of Technetium(V) and Rhenium(V) with β-Diketonates.

Reactions of (NBu)[MOCl] complexes (M = Tc or Re) with an excess of hexafluoroacetylacetone (Hhfac) give products with a composition of (NBu)[MOCl(hfac)] as bright yellow (Tc) or red (Re) solids. The products are stable as solids but rapidly decompose in solution. A number of related phenylimidorhenium(V) complexes were synthesized starting from [Re(NPhF)Cl(PPh)], where (NPhF) is a para-fluorinated phenylimido ligand. Products with compositions of [Re(NPhF)Cl(PPh)(acac)], [Re(NPhF)Cl(PPh)(hfac)], [Re(NPhF)Cl(PPh)(tfac)], [Re(NPhF)Cl(PPh)(naphtfac)], and [Re(NPhF)Cl(PPh)(butfac)] (Hacac = acetylacetone, Htfac = trifluoroacetylacetone, Hnaphtfac = naphthoyltrifluoroacetylmethane, and Hbutfac = tert-butyroyltrifluoroacetylmethane) were isolated from reactions of the quite soluble [Re(NPhF)Cl(PPh)] with the corresponding β-diketones and studied spectroscopically and by X-ray diffraction. The β-diketonates are coordinated in a meridional arrangement with the phenylimide. The formation of two isomers was detected for nonsymmetric β-diketones with a preference for the "equatorial" position for the more bulky substituents. Products with more than one chelating ligand were not obtained. The technetium complexes [Tc(NPhX)Cl(PPh)] (X = p-F or p-CF) were prepared from reactions of pertechnetate, PPh, HCl, and substituted arylacetylhydrazines and isolated as green solids. They are sufficiently stable as solid but rapidly decompose in moist solvents upon hydrolysis of the Tc-N bonds. From reactions of [Tc(NPh)Cl(PPh)] or [Tc(NPhF)Cl(PPh)] in dry solvents, the complexes [Tc(NPh)Cl(PPh)(hfac)] and [Tc(NPhF)Cl(PPh)(hfac)] were prepared and isolated in crystalline form. An X-ray diffraction study shows that fluorination of the para position of the phenylimido ligand results in a slight lengthening of all bonds in the coordination sphere of technetium.