The [Re(CO)6]+ Cation as a Ligand-Transfer Reagent with Ferrocene Derivatives

Abstract

The [Re(CO) 6 ] + cation is a stable compound, soluble in aqueous media. We show that it can be used as a reagent in the synthesis of tricarbonyl(cyclopentadienyl)rhenium complexes. [Re(CO) 6 ] + reacts with ferrocene derivatives, particularly acetylferrocene, in DMSO, DMF or a water/DMSO (1:1)

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“…Ferrocene amides were prepared by amide formation between amines and ferrocene carboxylic acid derivatives, generally in the presence of a base to prevent protonation of the attacking nucleophile 20. In our case, N ‐phenylferrocenecarboxamide ligand 2 was first prepared according to a previously reported one‐pot procedure19 by in situ activation of ferrocene carboxylic acid by oxalyl chloride and then reaction of the formed ferrocenoyl chloride with an excess of aniline at ambient temperature (Scheme ). With this method, the molecule 2 was prepared in 64% yield.…”

“… Synthesis of 2 : (i) oxalyl chloride, CH 2 Cl 2 , 0 °C then 4 h at ambient temperature, 97%; (ii) aniline, Hünig's base, THF, ambient temperature, 4 h, 96%; (iii) Top et al ,19 64% …”

“…Depending of both the nature of the ferrocene derivatives and the oxidation state of the metallic precursor, different synthetic strategies (via double‐ligand transfer13, 24, 25 or single‐ligand transfer reactions18, 25–27) were described for the preparation of ‘CpM(CO) 3 ’‐type complexes (M = 99m Tc or Re) from ferrocene derivatives. Jaouen's team reported recently the preparation of complex Re‐2 in 43% yield via a single‐ligand transfer using the water‐soluble cation Re(CO) 6 + as Re I (CO) 3 source 19. Nevertheless, the [Re(CO) 6 ][BF 4 ] salt is not commercially available and requires toxic sodium amalgam for its synthesis 28.…”

“…As a proof of example, Tc‐complex 99m Tc‐2 , synthesized from N ‐phenylferrocenecarboxamide 2 , was evaluated as a new model of cytectrene (Scheme ). If the synthesis of the molecule 2 was previously reported by Jaouen’s team,19 to the best of our knowledge, no preparation and evaluation of the corresponding 99m Tc‐complex have been described. In this contribution, an improved synthesis of the ligand 2 and its characterization including the solid‐state structure, as well as the preparation of the corresponding CpM(CO) 3 complexes on the macroscopic scale (M = Re) and radiotracer scale (M = 99m Tc), are presented.…”

New neutral and lipophilic technetium complexes based on a cytectrene moiety: synthesis, characterization and biological evaluation

“…It is noteworthy that using the standard one-step amidation [18], , -bis(methoxyphenyl)ethanediamide side products [19] were observed for the synthesis of 2 and 3 in nonnegligible yield (20%-35%). All the purified ligands were characterised by MS, elemental analysis, proton and carbon NMR spectroscopies, as outlined in Table 1, and presented expected structural features.…”