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

Reactions of (NBu₄)[MOCl₄] complexes (M = Tc or Re) with an excess of hexafluoroacetylacetone (Hhfac) give products with a composition of (NBu₄)[MOCl₃(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)Cl₃(PPh₃)₂], where (NPhF)^2- is a para-fluorinated phenylimido ligand. Products with compositions of [Re(NPhF)Cl₂(PPh₃)(acac)], [Re(NPhF)Cl₂(PPh₃)(hfac)], [Re(NPhF)Cl₂(PPh₃)(tfac)], [Re(NPhF)Cl₂(PPh₃)(naphtfac)], and [Re(NPhF)Cl₂(PPh₃)(^tbutfac)] (Hacac = acetylacetone, Htfac = trifluoroacetylacetone, Hnaphtfac = naphthoyltrifluoroacetylmethane, and H^tbutfac = tert-butyroyltrifluoroacetylmethane) were isolated from reactions of the quite soluble [Re(NPhF)Cl₃(PPh₃)₂] 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)Cl₃(PPh₃)₂] (X = p-F or p-CF₃) were prepared from reactions of pertechnetate, PPh₃, 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)Cl₃(PPh₃)₂] or [Tc(NPhF)Cl₃(PPh₃)₂] in dry solvents, the complexes [Tc(NPh)Cl₂(PPh₃)(hfac)] and [Tc(NPhF)Cl₂(PPh₃)(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.