[Tc(NO)(Cp)(PPh3)Cl] and [Tc(NO)(Cp)(PPh3)(NCCH3)](PF6), and Their Reactions with Pyridine and Chalcogen Donors.

Reactions of the technetium(I) nitrosyl complex [Tc(NO)(Cp)(PPh3)Cl] with triphenylphosphine chalcogenides EPPh3 (E = O, S, Se), and Ag(PF6) in a CH2Cl2/MeOH mixture (v/v, 2/1) result in an exchange of the chlorido ligand and the formation of [Tc(NO)(Cp)(PPh3)(EPPh3)](PF6) compounds. The cationic acetonitrile complex [Tc(NO)(Cp)(PPh3)(NCCH3)]+ is formed when the reaction is conducted in NCCH3 without additional ligands. During the isolation of the corresponding PF6- salt a gradual decomposition of the anion was detected in the solvent mixture applied. The yields and the purity of the product increase when the BF4- salt is used instead. The acetonitrile ligand is bound remarkably strongly to technetium and exchange reactions readily proceed only with strong donors, such as pyridine or ligands with 'soft' donor atoms, such as the thioether thioxane. Substitutions on the cyclopentadienyl ring do not significantly influence the ligand exchange behavior of the starting material. 99Tc NMR spectroscopy is a valuable tool for the evaluation of reactions of the complexes of the present study. The extremely large chemical shift range of this method allows the ready detection of corresponding ligand exchange reactions. The observed 99Tc chemical shifts depend on the donor properties of the ligands. DFT calculations support the discussions about the experimental results and provide explanations for some of the unusual findings.

Pertechnetates - A Structural Study Across the Periodic Table.

The number of crystal structures of pertechnetates derived from aqueous solutions has been expanded from seven to over 30. We report the conversion of NH4TcO4 to aqueous HtcO4 via acidic cation exchange. This is followed by the synthesis and structural elucidation of pertechnetate salts of alkaline earth (AE), transition metal I and lanthanoids (Ln) elements. Various degrees of hydration and coordination are discussed. Where possible, a comparison with the perrhenate homologues is made. The described syntheses and materials may be used as novel starting materials for extended technetium research.

Technetium Complexes with an Isocyano-alkyne Ligand and Its Reaction Products.

The attachment of an ethyne substituent in the para position of phenylisocyanide, CNPhpC≡CH, enables the isocyanide to replace carbonyl ligands in the coordination sphere of common technetium(I) starting materials such as (NBu4)[Tc2(µ-Cl)3(CO)6]. The ligand exchange proceeds under thermal conditions and finally forms the corresponding hexakis(isocyanide)technetium(I) complex. The product undergoes a copper-catalyzed cycloaddition ("Click" reaction), e.g., with benzyl azide, which gives the [Tc(CNPhazole)6]+ cation. The free, uncoordinated "Click" product is obtained from a reaction of the corresponding tetrakis(CNPhazole)copper(I) complex and NaCN. It readily reacts with mer-[Tc(CO)3(tht)(PPh3)2](BF4) (tht = tetrahydrothiophene) under exchange of the thioether ligand. Alternatively, [Cu(CNPhazole)4]+ can be used as a transmetalation reagent for the synthesis of the hexakis(isocyanide)technetium(I) complex, which is the preferable approach for the synthesis of the technetium complex with the short-lived nuclear isomer 99mTc, and a corresponding protocol for [99mTc(CNPhazole)6]+ is reported. The 99Tc and copper complexes have been studied by single-crystal X-ray diffraction and/or spectroscopic methods including IR and multinuclear NMR spectroscopy.

Phenylimido complexes of rhenium: fluorine substituents provide protection, reactivity, and solubility.

Reactions of [Re(NPhF)Cl3(PPh3)2] ({NPhF}2- = p-fluorophenylimide) with a variety of alkyl and aryl isocyanides have been studied. Different reactivity patterns and products have been obtained depending on the steric and electronic properties of the individual ligands. This involves the formation of 1 : 1 and 1 : 2 exchange products of Re(V) with the general formulae mer-[Re(NPhF)Cl3(PPh3)(isocyanide)] and cis- or trans-[Re(NPhF)Cl3(isocyanide)2]. The stability of the obtained products is correlated with the substitution pattern of the isocyanide ligands. The products have been studied by single-crystal X-ray diffraction and spectroscopic methods, including IR and multinuclear NMR spectroscopy as well as mass spectrometry. The use of partially fluorinated starting materials and ligands allows the modulation of the solubilities of the starting materials and the products as well as the monitoring of the reactions by means of 19F NMR. The attachment of the CF3 or F substituent on the isocyanides gives control over the steric bulk and the electronic properties of the ligands and, thus, their reactivity.

[ReH3 (PPh3 )4 ] - A Key Compound in the Rhenium Hydride Chemistry.

The chemistry of the rhenium trihydrido complex [ReH3 (PPh3 )4 ] (1) has been reinvestigated. An improved synthesis and the solid-state structure of the compound as well as several reactions are reported. The solid-state structure of 1 is similar to that of [TcH3 (PPh3 )4 ] having a capped-octahedral coordination sphere. The PPh3 ligands surround the Re atom in a trigonal-pyramidal mode with a short apical Re-P bond (2.300(2) Å) and three longer basal bonds (2.429(2)-2.449(2) Å). Reactions of 1 with monodentate phosphines such as PMe3 or PBu3 give the mono-substituted complexes [ReH3 (PPh3 )3 (PMe3 )] (2) and [ReH3 (PPh3 )3 (PBu3 )] (3) under retention of the apical PPh3 ligand and substitution of one of the basal PPh3 ligands. The stability of the phosphine trihydride complexes decreases in the order PPh3 >PMe3 >PBu3 . Treatment of [ReH3 (PPh3 )4 ] with trityl hexafluorophosphate in CH3 CN does not result in a hydride abstraction, but gives the tetrahydrido cation [ReH4 (NCCH3 )(PPh3 )3 ]+ (4), while reactions with nitriles give unstable azavinylidene complexes of the composition [ReH2 (PPh3 )3 (NC(H)R)] (5). They are formed by an insertion of the nitrile into a Re-H bond. The solid-state structure of the methyl derivative [ReH2 (PPh3 )3 (NC(H)CH3 )] (5 a) was determined showing a linear Re-N-C unit with rhenium-nitrogen and nitrogen-carbon double bonds, while the N=CH-C bond is clearly bent with an angle of 124°. Two previously unknown polymorphs of [ReH5 (PPh3 )3 ] were isolated from reactions of 1 with HOC6 H3 (CH3 )2 and thiourea after prolonged heating in toluene and characterized by IR spectroscopy and X-ray diffraction.

The Chemistry of Phenylimidotechnetium(V) Complexes with Isocyanides: Steric and Electronic Factors.

Organometallic approaches are of ongoing interest for the development of novel functional 99mTc radiopharmaceuticals, while the basic organotechnetium chemistry seems frequently to be little explored. Thus, structural and reactivity studies with the long-lived isotope 99Tc are of permanent interest as the foundation for further progress in the related radiopharmaceutical research with this artificial element. Particularly the knowledge about the organometallic chemistry of high-valent technetium compounds is scarcely developed. Here, phenylimido complexes of technetium(V) with different isocyanides are introduced. They have been synthesized by ligand-exchange procedures starting from [Tc(NPh)Cl3(PPh3)2]. Different reactivity patterns and products have been obtained depending on the steric and electronic properties of the individual ligands. This involves the formation of 1:1 and 1:2 exchange products of Tc(V) with the general formulae [Tc(NPh)Cl3(PPh3)(isocyanide)], cis- or trans-[Tc(NPh)Cl3(isocyanide)2], but also the reduction in the metal and the formation of cationic technetium(I) complex of the formula [Tc(isocyanide)6]+ when p-fluorophenyl isocyanide is used. The products have been studied by single-crystal X-ray diffraction and spectroscopic methods, including IR and multinuclear NMR spectroscopy. DFT calculations on the different isocyanides allow the prediction of their reactivity towards electron-rich and electron-deficient metal centers by means of the empirical SADAP parameter, which has been derived from the potential energy surface of the electron density on their potentially coordinating carbon atoms.

Mixed-Isocyanide Complexes of Technetium under Steric and Electronic Control.

Reactions of the alkyl isocyanide fac-[Tc(CO)3(CNR)2Cl] complexes (2) (CNR = CNnBu or CNtBu) with the sterically encumbered isocyanide CNp-FArDarF2 [DArF = 3,5-(CF3)2C6H3] allow a selective exchange of the carbonyl ligands of 2 and the isolation of the mixed-isocyanide complexes mer,trans-[Tc(CNp-FArDarF2)3(CNR)2Cl] (3). Depending on the steric requirements of the residues R, the remaining chlorido ligand can be replaced by another isocyanide ligand. Cationic complexes such as mer-[Tc(CNp-FArDarF2)3(CNnBu)3]+ (4a) or mer,trans-[Tc(CNp-FArDarF2)3(CNnBu)2(CNtBu)]+ (6) have been prepared in this way and isolated as their PF6- salts. mer,trans-[Tc(CNp-FArDarF2)3(CNnBu)2(CNtBu)](PF6) represents to the best of our knowledge the first transition-metal complex with three different isocyanides in its coordination sphere. Since the degree of the ligand exchange seems to be controlled both by the electronic and steric measures of the incoming isocyanides, we undertook similar reactions with the sterically less demanding p-fluorophenyl isocyanide, CNPhpF, which indeed readily led to the hexakis(isocyanide)technetium(I) cation through an exchange of all ligands in the staring materials [Tc2(CO)6(µ-Cl)3]- or fac-[Tc(CO)3(CNR)2Cl]. The influence of the substituents at the isocyanide ligands in such reactions has been reasoned with the density functional theory-derived electrostatic potential at the accessible surface of the corresponding isocyanide carbon atoms.

Unlocking Air- and Water-Stable Technetium Acetylides and Other Organometallic Complexes.

The first technetium complexes containing anionic alkynido ligands in an end-on coordination mode have been prepared by using the nonprotic, cationic precursor mer,trans-[Tc(SMe2)(CO)3(PPh3)2]+. This cation acts as a functional analogue of the highly reactive 16-electron metallo Lewis acid {Tc(CO)3(PPh3)2}+ in reactions with alkynes, acetylides, and other organometallic reagents. Such reactions give a variety of organometallic technetium complexes in excellent yields and enable the preparation of [Tc(CH3)(CO)3(PPh3)2], [Tc(Ph)(CO)3(PPh3)2], [Tc(Cp)(CO)2(PPh3)], [Tc(═CCH2CH2CH2O)(CO)3(PPh3)2]+, [Tc(═CCH2CH2CH2CH2O)(CO)3(PPh3)2]+, [Tc(C≡C-H)(CO)3(PPh3)2], [Tc(C≡C-Ph)(CO)3(PPh3)2], [Tc(C≡C-tBu)(CO)3(PPh3)2], [Tc(C≡C-nBu)(CO)3(PPh3)2], [Tc(C≡C-SiMe3)(CO)3(PPh3)2], and [Tc{C≡C-C6H3(CF3)2}(CO)3(PPh3)2]. The bonding situation in the alkynyl complexes is compared to that in corresponding alkyl- and arylnitrile and -isonitrile complexes. [Tc(N≡C-Ph)(CO)3(PPh3)2](BF4), [Tc(C≡N-Ph)(CO)3(PPh3)2](BF4), [Tc(N≡C-tBu)(CO)3(PPh3)2](BF4), and [Tc(C≡N-tBu)(CO)3(PPh3)2](BF4) were prepared in high yields by ligand exchange reactions starting from mer,trans-[Tc(OH2)(CO)3(PPh3)2](BF4). The novel complexes were characterized by single-crystal X-ray diffraction and spectroscopic methods. In particular, 99Tc nuclear magnetic resonance spectroscopy proved to be an invaluable and sensitive tool for the characterization of the complexes. Density functional theory calculations strongly suggest similar bonding situations for the related alkynyl, nitrile, and isonitrile complexes of technetium.

Solvents and Ligands Matter: Structurally Variable Palladium and Nickel Clusters Assembled by Tridentate Selenium- and Tellurium-Containing Schiff Bases.

Structurally variable organochalcogen clusters containing palladium(II) and nickel(II) ions were assembled starting from the salicylidene-substituted dichalcogenides (Y-C6H4-N═CH-C6H4-OH)2 ({HLY}2, where Y = Se or Te), and palladium or nickel acetate. The tetrameric palladium clusters contain reduced chalcogenolato ligands {Y-C6H4-N═CH-C6H4-O)}2- ({L'Y}2-, where Y = Se or Te), while the initially formed trimeric nickel clusters contain the intact, coordinated dichalcogenides. The palladium clusters have a general formula of [Pd4(L'Y)4] and represent the first examples of palladium complexes where both a gyrobifastigial and a pseudocubane arrangement of the central Pd4Y4 unit could be established with the same ligand, only depending on the solvents used for crystallization. Reduced density gradient (RDG) considerations based on density functional theory calculations suggest that the commonly referred to stabilizing chalcogen-palladium or palladium-palladium interactions for the two geometric arrangements are weak van der Waals contacts resulting from the contact of two nonbinding lone pairs. In the case of the pseudocubane arrangement, a repulsive steric effect, which is indicated by RDG analysis, is clearly supported by the cuplike distortions detected in the solid-state structure of the compound. In contrast to the reactions with palladium acetate, where the dichalcogenides were cleaved, during similar reactions with nickel acetate, the dichalcogenides remained intact and trimeric clusters of the composition [Ni-µ2-κ2-(Ni{κ5-LY}2)2-µ2-(OAc)2] (Y = Se, Te) were formed. Air oxidation and hydrolysis of [Ni-µ2-κ2-(Ni{κ5-LTe}2)2-µ2-(OAc)2] gave a rare example of a hexanuclear nickel cluster of the composition [Ni2-κ5-(Ni4-κ6-µ6-{(L'Te2O3)(L'TeO2)2}2)-µ2-(H2O)2], which is composed of a well-defined framework consisting of tellurinic anhydride and tellurinate units, which proves the comparably higher oxidation sensitivity of the trinickel dichalcogenide complexes. Electron spray ionization mass spectrometry spectra of both the palladium and nickel clusters indicate that they show fluctional behavior with varying nuclearity in solution and can adopt multiple charge states especially because of the noninnocence of the chalcogen-based ligands. The complexes were fully characterized by spectroscopic methods, elemental analyses, and X-ray diffraction.

Technetium(I) Carbonyl Chemistry with Small Inorganic Ligands.

[Tc(OH2)(CO)3(PPh3)2](BF4) has been used as a synthon for reactions with small inorganic ligands with relevance for the treatment of nuclear waste solutions such as nitrate, nitrite, pseudohalides, permetalates (M = Mn, Tc, Re), and BH4-. The formation of bond isomers and/or a distinct reactivity has been observed for most of the products. [Tc(NCO)(CO)3(PPh3)2], [Tc(NCS)(CO)3(PPh3)2], [Tc(CN)(CO)3(PPh3)2], [Tc(N3)(CO)3(PPh3)2], [Tc(NCO)(OH2)(CO)2(PPh3)2], [Tc(η2-OON)(CO)2(PPh3)2], [Tc(η1-NO2)(CO)3(PPh3)2], [Tc(η2-OONO)(CO)2(PPh3)2], [Tc(η1-ONO2)(CO)3(PPh3)2], [Tc(η2-OO(CCH3))(CO)2(PPh3)2], [Tc(η2-SSC(SCH3))(CO)2(PPh3)2], [Tc(η2-SSC(OCH3))(CO)2(PPh3)2], [Tc(η2-SSC(CH3))(CO)2(PPh3)2], [Tc(η2-SS(CH))(CO)2(PPh3)2], [Tc(OTcO3)(acetone)(CO)2(PPh3)2], [Tc(OTcO3)(CO)3(PPh3)2], and [Tc(η2-HHBH2)(CO)2(PPh3)2] have been isolated in crystalline form and studied by X-ray crystallography. Additionally, the typical reactivity patterns (isomerization, thermal decomposition, hydrolysis, or decarbonylation) of the products have been studied by spectroscopic methods. 99Tc NMR spectroscopy has proved to be a particularly useful tool for the evaluation of such reactions of the diamagnetic technetium(I) compounds in solution.

Ammonium Pertechnetate in Mixtures of Trifluoromethanesulfonic Acid and Trifluoromethanesulfonic Anhydride.

Ammonium pertechnetate reacts in mixtures of trifluoromethanesulfonic anhydride and trifluoromethanesulfonic acid under final formation of ammonium pentakis(trifluoromethanesulfonato)oxidotechnetate(V), (NH4 )2 [TcO(OTf)5 ]. The reaction proceeds only at exact concentrations and under the exclusion of air and moisture via pertechnetyl trifluoromethanesulfonate, [TcO3 (OTf)], and intermediate TcVI species. 99 Tc nuclear magnetic resonance (NMR) has been used to study the TcVII compound and electron paramagnetic resonance (EPR), 99 Tc NMR and X-ray absorption near-edge structure (XANES) experiments indicate the presence of the reduced technetium species. In moist air, (NH4 )2 [TcO(OTf)5 ] slowly hydrolyses under formation of the tetrameric oxidotechnetate(V) (NH4 )4 [{TcO(TcO4 )4 }4 ] ⋅10 H2 O. Single-crystal X-ray crystallography was used to determine the solid-state structures. Additionally, UV/Vis absorption and IR spectra as well as quantum chemical calculations confirm the identity of the species.

[Tc(OH2)(CO)3(PPh3)2]+: A Synthon for Tc(I) Complexes and Its Reactions with Neutral Ligands.

A scalable synthesis of the novel and highly reactive [Tc(OH2)(CO)3(PPh3)2]+ cation is described. The ligand-exchange chemistry of this compound with neutral ligands coordinating through C, N, O, S, Se, and Te has been explored systematically. The complexes either retain the original mer-trans tricarbonyl core under exclusive exchange of the aqua ligand or form dicarbonyl complexes by thermal decarbonylation. Ligand exchange reactions starting from [Tc(OH2)(CO)3(PPh3)2]+ proceed under mild conditions and are generally almost quantitative. Some of the formed complexes are remarkably stable and inert, while others provide products with one labile ligand for further reactions. The derived complexes of the type [Tc(L)(CO)3(PPh3)2]+ and [Tc(L)2(CO)2(PPh3)2]+ represent an interesting opportunity for the development of 99mTc complexes with potential use in radiopharmacy. The ready displacement of the aqua ligand highlights the synthetic value of [Tc(OH2)(CO)3(PPh3)2]+ as a reactive entry point for further studies in the little explored field of the organometallic chemistry of technetium.

Large Telluroxane Bowls Connected by a Layer of Iodine Ions.

Phenyltelluroxane clusters of the composition [{(PhTe)19 O24 }2 I18 (solv)] (1) are formed during the hydrolysis of [PhTeI3 ]2 or the oxidation of various phenyltellurium(II) compounds with iodine under hydrolytic conditions. The compounds consist of two half-spheres with a {(PhTe)19 O24 }9+ network, which are connected by 18 iodine atoms. The spherical clusters can accommodate solvent molecules such as pyridine or methanol in the center of two rings formed by iodine atoms. The presence of other metal ions during the cluster formation results in a selective replacement of the central {PhTe}3+ units of each half-sphere as has been demonstrated with the isolation of [{(PhTe)18 ({Ca(H2 O)2 }O24 }2 I16 ] (2) and [{(PhTe)18 ({Y(NO3 )(H2 O)}O24 }2 I16 ] (3). A crownether-like coordination by six oxygen atoms of the telluroxane network is found for the {Ca(H2 O}2 }2+ and {Y(NO3 )(H2 O)}2+ building blocks. Mass spectrometric studies show that considerable amounts of the intact clusters are transferred to the gas phase without dissociation.

Effect of Fluorination on the Structure and Anti-Trypanosoma cruzy Activity of Oxorhenium(V) Complexes with S,N,S-Tridentate Thiosemicarbazones and Benzoylthioureas. Synthesis and Structures of Technetium(V) Analogues.

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.