Mixed isocyanide/carbonyl complexes with rhenium in the oxidation states “+1”, “0” and “−1” were prepared assisted by a sterically encumbered.

Metrics & More Article Recommendations * sı Supporting Information ABSTRACT: [Re(CO)Br(CNAr DArF2 ) 4 ] and [Tc(CO)Cl-(CNAr DArF2 ) 4 ] (Ar DArF = 2,6-(3,5-(CF 3 ) 2 C 6 H 3 ) 2 -4-F-C 6 H 2 ) were prepared by reactions of [Re(CO) 5 Br] or (NBu 4 )[Tc 2 (CO) 6 (μ-Cl) 3 ] with the sterically encumbered isocyanide CNAr DArF2 . These two compounds proved to be excellent starting materials for the synthesis of unprecedented low-valent rhenium and technetium complexes. The reduction of [Re(CO)Br(CNAr DArF2 ) 4 ] with Na/ Hg produces an equimolar mixture of [Re(CO)(CNAr DArF2 ) 4 ] and Na[Re(CO)(CNAr DArF2 ) 4 ] containing the transition metal in the formal oxidation states "0" and "−1", respectively. The reduction of [Tc(CO)Cl(CNAr DArF2 ) 4 ] with Na/Hg produces Na[Tc(CO)-(CNAr DArF2 ) 4 ], which was characterized by 19 F and 99 Tc NMR spectroscopy. The reactivity of Na[Re(CO)(CNAr DArF2 ) 4 ] resembles that of [Re(CO) 5 ] − , proved by reactions with a number of electrophiles such as MeI, HCl, or F 6 C 5 C(O)Cl.

A series of technetium complexes with the sterically encumbered m-terphenyl isocyanides CNAr Dipp2 (Dipp = 2,6diisopropylphenyl) and CNAr Mes2 (Mes = 2,4,6-trimethylphenyl) has been prepared. The products span three different oxidation states (+1, +3, and +5) of the radioactive transition metal and comprise carbonyl, nitrosyl, chloride, and nitrido complexes. All members of this series (trans,mer-[Tc I (CO) 3 Cl(CNAr Dipp2 )], trans-[Tcand trans-[Tc V (NPh)X 2 (CNAr Dipp2 ) 2 ] (X = Cl, Br)) are stable under ambient conditions. The ν CN IR frequencies measured for the complexes frequently appear at wavenumbers higher than those for the uncoordinated isocyanides, which suggests a low degree of back-donation into the CN π* orbitals of these ligands.

A series of 16 “3 + 2” mixed-ligand complexes of the general composition [ReO­(L1)­(L2)] (H2L1a–H2L1d = tridentate thiosemicarbazones having a phenyl group with 4-H, 4-F, 3,5-di-F, and 4-CF3 substituents; HL2a–HL2d = bidentate N,N-diethyl-N′-benzoylthioureas with 4-H, 4-F, 3,5-di-F, and 4-CF3 substituents at the benzoyl groups) have been synthesized and characterized by spectroscopic methods and X-ray diffraction. Irrespective of the individual fluorine substitution, the complexes are stable and possess the same general structure. Some systematic electronic effects of the fluorine-substitution patterns of the ligands have been found on the 13C NMR chemical shifts of the N–CN carbon atoms of the {L1}2– and the CO carbon atoms of the {L2}− ligands. Antiparasitic properties of the rhenium complexes have been tested against epimastigotes and trypomastigotes forms of two Trypanosoma cruzi strains and the amastigotes form of one of them. The results of this study indicate that the activity of the rhenium complexes can clearly be modulated by fluorine substitution of their ligands. Some of the fluorinated compounds show a high activity against epimastigotes and trypomastigotes forms of the parasites. Reactions between (NBu4)­[TcOCl4] and two representatives of the fluorinated ligands (H2L1b, 4-F-substituted, and H2L1c, 4-CF3-substituted) form stable complexes of the composition [TcOCl­(L1b)] and [TcOCl­(L1c)]. Subsequent reactions of these products with HL2b (4-F-substituted) give the corresponding [TcO­(L1)­(L2)] mixed-ligand complexes. Also, the technetium compounds are stable as solids and in solutions and have structures corresponding to those of their rhenium analogues.

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