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

Abstract

A series of technetium complexes with (η5-cyclopentadienyl)­tris­(dimethyl phosphito-P)­cobaltate­(III), also known as the “Kläui ligand” {LOMe}−, has been prepared. The products span seven different oxidation states (+1 to +7) of the radioactive transition metal and comprise nitrosyl, halide, oxido and nitrido complexes. All members of this series ([TcI(NO)­Cl­(PPh3)­(LOMe)], [TcII(NO)­Cl2(LOMe)], [TcIIICl2(PPh3)­(LOMe)], [TcIVCl3(LOMe)], [TcVOCl2(LOMe)], [TcVNCl­(PPh3)­(LOMe)], [TcVINCl2(LOMe)], and [TcVIIO3(LOMe)] are air- and water-stable compounds, which recommends this class of technetium complexes as potential candidates for nuclear medical imaging procedures.

[Tc(NO)Cl(Cp)(PPh3)] – A Technetium(I) Compound with an Unexpected Synthetic Potential

“…Besides the septet of the PF 6 − counter ion, the 31 P NMR spectrum of the product shows two resonances at 32.1 (coordinated PMe 3 ) and 27.9 ppm (coordinated PPh 3 ). They are surprisingly narrow and well resolved, which is not common for 31 P NMR spectra of technetium compounds, where frequently an extreme line‐broadening is observed due to scalar couplings between the 31 P and 99 Tc nuclei [36,37] …”

[{TcI(NO)(LOMe)(PPh3)Cl}2Ag](PF6) and [TcII(NO)(LOMe)(PPh3)Cl](PF6): Two Unusual Technetium Complexes with a “Kläui‐type” Ligand

“…The starting material [Tc(NO)(L OMe )(PPh 3 )Cl] (2) can be prepared from a simple ligand exchange reaction between [Tc-(NO)Cl 2 (PPh 3 ) 2 (CH 3 CN)] and NaL OMe in reasonable yields and with high purity. [22] No redox processes or the formation of considerable amounts of side-products have been observed during the synthesis. The compound is stable in air, but cyclic voltammetry gave evidence for a quasi-reversible one-electron oxidation with a half-wave potential of À 0.16 V vs. ferrocene.…”

“…The compound is stable in air, but cyclic voltammetry gave evidence for a quasi-reversible one-electron oxidation with a half-wave potential of À 0.16 V vs. ferrocene. [22] An attempted oxidation of 2 with Cl 2 gave a mixture of various Tc(II) nitrosyl complexes, where one of which could be assigned to the [Tc(NO)Cl 4 (solvent)] À anion on the basis of its EPR data. [24] A more selective formation of a Tc(II) complex is obtained when solutions of 2 in THF or CH 2 Cl 2 are exposed to Ag(PF 6 ).…”

“…The IR spectra of the more electron-rich technetium(I) complexes show their ν NO absorptions at clearly lower frequencies due to a higher degree of back-donation from orbitals of the d 6 Tc(I) ion into antibonding orbitals of the NO ligand. [22,24,25] The d 5 "low-spin" configuration of Tc(II) allows the detection of resolved EPR spectra. Figure 2 depicts the spectra obtained for compound 3.…”

“…[18][19][20][21] A variety of technetium complexes with the "Kläui-type" ligand η 5 cyclopentadienyltris(dimethyl phosphito-P)cobaltate(III) ({L OMe } À ), comprising seven different oxidation states of the transition metal have been introduced recently. [22] The obtained products are of remarkable stability, which recommends them as starting materials for ongoing reactions. One of the isolated technetium(I) complexes, [Tc(NO)(L OMe )(PPh 3 )Cl] (2) in Figure 1, is structurally related to the cyclopentadienyl compound 1, for which we recently had to note some unexpected behavior.…”