Novel, Mercury-Free Synthetic Pathway for Trifluoromethylthio-Substituted Metallocenes

A novel
synthetic pathway for trifluoromethylthioferrocene (3), which does not involve the use of toxic mercury­(II)-based reagents,
is described. The novel approach involves first the treatment of the
commercially available bromoferrocene (1a) with NaSCN
in the presence of copper­(+I) to yield thiocyanatoferrocene (1), and then the reaction of 1 with the Rupper-Prakash
reagent and tetrabutylammonium fluoride (TBAF) to give 3 in an overall yield of 60%. This approach could be extended for
the preparation of thiocyanato-(4) and trifluoromethylthio-ruthenocene
(7), which are herein both reported for the first time.
Interestingly, diferrocenyl disulfide (2a) and diruthenocenyl
disulfide (5) could be isolated as side-products during
the synthesis of 3 and 7, respectively.
All new compounds were unambiguously characterized by 1H, 13C, and 19F NMR spectroscopy, mass spectrometry,
cyclic voltammetry, elemental analysis, as well by X-ray crystallography
for 1, 4, 4b, 5, 6, and 7. 1–7 were further tested for their toxic activity on cervical
cancer (HeLa) and noncancerous (MRC-5) cell lines. All organometallic
compounds were found either to be nontoxic or to have a moderate toxicity
toward the cell lines used in this study.