Multinuclear complexes or clusters are rarely investigated in medicinal inorganic chemistry although they represent structural intermediates between molecules and nanomaterials. We present in this report two strategies towards Tc-containing clusters. In a pre-assembly approach, the preformed but incomplete cluster fragment [Re (μ -OH) (μ -OH)(CO) ] reacts with [ Tc(CO) ] to the highly stable [ TcRe (μ -OH) (CO) ] cube. The same structure self-assembles when reacting the mononuclear Re and Tc precursors in one pot. Integrating the coordinating OH groups from Schiff bases in this concept leads straight to dinuclear, mixed-metal complexes of the type [ TcRe(μ -O^N-R ) (CO) ] in quantitative yields. Both strategies are unprecedented and open a future path towards clusters, incorporating a Tc radiolabel while being decorated with targeting or cytotoxic moieties.
The labeling of (bio)molecules with metallic radionuclides such as 99mTc demands conjugated, multidentate chelators. However, this is not always necessary since phenyl rings can directly serve as integrated, organometallic ligands. Bis‐arene sandwich complexes are generally prepared by the Fischer–Hafner reaction. In extension of this, we show that [99mTc(η6‐C6R6)2]+‐type complexes are directly accessible from water and [99mTcO4]−, even using arenes incompatible with Fischer–Hafner conditions. To unambiguously confirm the nature of these unprecedented 99mTc complexes, their rhenium homologous have been prepared by substituting naphthalene ligands in [Re(η6‐C10H8)2]+ with the corresponding phenyl groups. The ease with which highly stable [99mTc(η6‐C6R6)2]+ complexes are formed under standard labeling conditions enables a multitude of new potential imaging agents based on commercial pharmaceuticals or lead structures.
<sup>The chemistry of rhenium complexes covers oxidation state +VII to -I. Some oxidation states such as +II are only rarely found in literature. One of the reasons is the lack of a suitable stable precursor for the oxidation state +II. However, we have developed a two step synthesis to the fully solvated Re(+II) complex [Re(NCCH</sup><sub>3</sub><sup>)</sup><sub>6</sub><sup>]</sup>2+<sup> from [ReO</sup><sub>4</sub><sup>]</sup>-<sup> via the rhenium bis-arene complex [Re(C</sup><sub>10</sub><sup>H</sup><sub>8</sub><sup>)</sup><sub>2</sub><sup>]</sup>+<sup>. This fully solvated Re(+II) was fully characterized by various spectroscopic manners, cyclic voltammetry, and X-Ray diffraction analysis. Its potential as a precursor for Re(+II) chemistry was explored with various substitutions reactions with phosphines and halides, and the obtained products were as well fully characterized.<br></sup>
The labeling of (bio)molecules with metallic radionuclides such as 99mTc demands conjugated, multidentate chelators. However, this is not always necessary since phenyl rings can directly serve as integrated, organometallic ligands. Bis‐arene sandwich complexes are generally prepared by the Fischer–Hafner reaction. In extension of this, we show that [99mTc(η6‐C6R6)2]+‐type complexes are directly accessible from water and [99mTcO4]−, even using arenes incompatible with Fischer–Hafner conditions. To unambiguously confirm the nature of these unprecedented 99mTc complexes, their rhenium homologous have been prepared by substituting naphthalene ligands in [Re(η6‐C10H8)2]+ with the corresponding phenyl groups. The ease with which highly stable [99mTc(η6‐C6R6)2]+ complexes are formed under standard labeling conditions enables a multitude of new potential imaging agents based on commercial pharmaceuticals or lead structures.
The oxidation of [Re( 6 -C10H8)2] + with Ag I in acetonitrile yields [Re(NCCH3)6] 2+ . This fully solvated Re II compound was characterized by spectroscopic methods and X-ray structure analyses. We show that [Re(NCCH3)6] 2+ acts as a precursor complex for a variety of substitution reactions. Treatment with monodentate triphenyl phosphine (PPh3) and bidentate 1,2bis(diphenylphosphino)ethane (dppe) yields the Re I complexes [trans-Re(PPh3)2(NCCH3)4] 2+ and [trans-Re(dppe)2(NCCH3)2] + , respectively. [trans-Re(dppe)2(NCCH3)2] + is oxidized under mild conditions by Ag I to its Re II analogue [trans-Re(dppe)2(NCCH3)2] 2+ . Reactions of [Re(NCCH3)6] 2+ with a halide mixture consisting of NaX and AgX (X = Cl, I) results in the formation of the corresponding Re III complexes [trans-ReX2(NCCH3)4] + . [trans-ReBr2(NCCH3)4] + can be obtained directly from [Re( 6 -C10H8)2] + by oxidation with FeBr3 in acetonitrile. The title compound is thus a convenient starting material for Re II and Re III complexes by simple solvent exchange, which are otherwise difficult to access.
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