One Ligand, One Metal, Seven Oxidation States: Stable Technetium Complexes with the “Kläui Ligand”

[Tc(NO)Cl2(PPh3)2(CH3CN)] and Its Reactions with 2,2'-Dipyridyl Dichalcogenides

The sparingly soluble technetium(I) complex [TcI(NO)Cl2(PPh3)2(CH3CN)] (1) slowly dissolves during reactions with 2,2'-dipyridyl ditelluride, (2-pyTe)2, 2,2'-dipyridyl diselenide, (2-pySe)2, or 2,2'-dipyridyl disulfide, (2-pyS)2, under formation of deeply colored solutions. Blue (Te compound) or red solids (Se compound) of the composition [{TcI(NO)Cl2(PPh3)2}2{µ2-(2-pyE)2}], E = Te (3), Se (4), precipitate from the reaction solutions upon addition of toluene. They represent the first technetium complexes with dichalcogenides. While [{TcI(NO)Cl2(PPh3)}2{µ2-(2-pyTe)2}] (3) is the sole product, a small amount of a second product, [TcII(NO)Cl2(PPh3)(2-pySe)] (5), was obtained from the respective mother solution of the reaction with the diselenide. From the corresponding reaction between 1 and (2-pyS)2, the technetium(II) compound, [TcII(NO)Cl2(PPh3)(2-pyS)] (6), could be isolated exclusively. The products were studied by single-crystal X-ray diffraction and spectroscopic methods including 99Tc NMR for the technetium(I) products and EPR spectroscopy for the Tc(II) complexes. The experimental results are accompanied by DFT considerations, which help to rationalize the experimental observations.

Nitrosyl and Thionitrosyl Complexes of Technetium and Rhenium and Their Reactions with Hydrotris(pyrazolyl)borates

The very limited number of structurally known thionitrosyl complexes of technetium was increased by the synthesis of [TcII(NS)Cl3(PPh3)2] (3) and [TcII(NS)Cl3(PPh3)(OPPh3)] (4) and their reaction products with hydrotris(pyrazolyl)borates, {HB(pzR)3}-. Similar reactions were conducted with [TcI(NO)Cl2(PPh3)2(CH3CN)] and related rhenium thionitrosyls. Remarkably, most such reactions result in a rapid cleavage of the boron-nitrogen bonds of the ligands and the formation of pyrazole complexes of the two group 7 metals. Only one compound with an intact {HB(pzR)3}- ligand could be isolated: the technetium(I) complex [TcI(NO)Cl(PPh3){HB(pz)3}] (2). Other products show the coordination of one or four neutral pyrazole ligand(s) in the coordination spheres of technetium generated by thermal decomposition of the pyrazolylborates [TcI(NO)Cl2(PPh3)2(pzH)] (1) and [TcI(NS)Cl(pzHMe2)4]+ (5). Reactions with the corresponding thionitrosylrhenium complex [ReII(NS)Cl3(PPh3)2] require higher temperatures and only compounds with one pyrazole ligand, [ReI(NS)Cl2(PPh3)(pzHR)] (6a-6c), were isolated. The products were studied spectroscopically and by X-ray diffraction.

PuCl3{CoCp[OP(OEt)2]3}: transuranic elements entering the field of heterometallic molecular chemistry

Recent advances enabled the discovery of heterometallic molecules for many metals: main group, d-block, lanthanides, and some actinides (U, Th). These complexes have at least two different metals joined by bridging ligands or by direct metal-metal bonding interactions. They are attractive because they can enable chemical cooperativity between metals from different parts of the periodic table. Some heterometallics provide access to unique reactivity and others exhibit physical properties that cannot be accessed by homometallic species. We envisioned that transuranic heterometallics might similarly enable new transuranic chemistry, though synthetic routes to such compounds have yet to be developed. Reported here is the first synthesis of a molecular transuranic complex that contains plutonium (Pu) and cobalt (Co). Our analyses of PuCl3{CoCp[OP(OEt)2]3} showed Pu(iv) and Co(iii) were present and suggested that the Pu(iv) oxidation state was stabilized by the electron donating phosphite ligands. This synthetic method - and the demonstration that Pu(iv) can be stabilized in a heterobimetallic molecular setting - provides a foundation for further exploration of transuranic multimetallic chemistry.

[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.

Tin(II) and Tin(IV) Complexes Incorporating the Oxygen Tripodal Ligands [(η5-C5R5)Co{P(OEt)2O}3]-, (R = H, Me; Et = -C2H5) as Potent Inflammatory Mediator Inhibitors: Cytotoxic Properties and Biological Activities against the Platelet-Activating Factor (PAF) and Thrombin

Metal complexes displaying antiplatelet properties is a promising research area. In our methodology, Platelet-Activating Factor (PAF), the most potent lipid pro-inflammatory mediator, serves as a biological probe. The antiplatelet activity is exerted by the inhibition of the PAF-induced aggregation in washed rabbit platelets (WRPs) and in rabbit plasma rich in platelets (rPRPs). Herein, the synthesis and biological investigation of a series of organometallic tin(II) and tin(IV) complexes, featuring the oxygen tripodal Kläui ligands [(η⁵-C₅R₅)Co{P(OEt)₂O}₃]^-, {R = H, (L_OEt^-); Me (L*_OEt^-)}, are reported. Reaction of NaL_OEt (1a) and NaL*_OEt (1b) with SnCl₂, yielded the rare four-coordinate L_OEtSnCl (2a) and L*_OEtSnCl (2b) complexes. Accordingly, L_OEtSnPh₃ (3a) and L*_OEtSnPh₃ (3b) were prepared, starting from Ph₃SnCl. Characterization includes spectroscopy and X-ray diffraction studies for 2a, 2b and 3b. The antiplatelet activity of the lead complexes 2b and 3a (IC₅₀ = 0.5 μΜ) is superior compared to that of 1a and 1b, while both complexes display a pronounced inhibitory activity against thrombin (IC₅₀ = 1.8 μM and 0.6 μM). The in vitro cytotoxic activities of 3a and 2b on human Jurkat T lymphoblastic tumor cell line is higher than that of cisplatin.

[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.

Signatures of technetium oxidation states: a new approach

A general strategy for the determination of Tc oxidation state by a new approach involving X-ray absorption near edge spectroscopy (XANES) at the Tc L₃ edge is shown.