Diiron μ-aminocarbyne compounds, 1a-e, are prepared in two steps from Fe 2 Cp 2 (CO) 4 , negating the need for difficult purification procedures of intermediate species; they are efficiently isolated by alumina chromatography. Minor amounts of μ-aminocarbyne aryl isocyanide compounds, 2a-c, are obtained as side products. The structures of the cations in 1a,c,e are calculated using DFT; the carbyne carbon is generally predicted to be the thermodynamic site of hydride addition, in agreement with a previous experimental finding concerning 1a. Accordingly, the reaction of 1e with NaBH 4 affords a bridging aminocarbene complex, 4, in 85 % yield. Otherwise, the reaction of 1c with NaBH 4 yields the aminocarbyne-cyclopentadiene derivative 3 (70 %), presumably as a consequence of the [a] Scheme 1. Regioselective additions of nucleophiles to the diiron aminocarbyne complex 1a. Results and DiscussionThe commercial compound [Fe 2 Cp 2 (CO) 4 ] was reacted with the appropriate isocyanide, in a ca. 3:2 molar ratio, in acetonitrile solution. [16] The reactions with alkyl isocyanides were conducted under reflux conditions, whereas the reactions with aryl isocyanides proceeded at room temperature. The resulting mixtures were dried under vacuum and the residues were dissolved in dichloromethane and then treated with methyl triflate, thus affording the μ-aminocarbyne complexes 1a-e (Scheme 2). The difficult isolation of the monoisocyanide intermediates (see the Introduction) was unnecessary. The final products 1a-e were efficiently purified by alumina chromatography and were then isolated as microcrystalline, air-stable compounds in 65-92 % yields. The synthesis of 1c-e was accompanied by the side formation of minor products derived from di-isocyanide species, 2a-c. Compounds 2a-c were recovered by the chromatography in 3-12 % yields, although 2a was formerly reported as being Scheme 2. Synthesis of diiron μ-aminocarbyne complexes.Eur. J. Inorg. Chem. 2018, 960-971 www.eurjic.org

Although ferrocene derivatives have attracted considerable attention as possible anticancer agents, the medicinal potential of diiron complexes has remained largely unexplored. Herein, we describe the straightforward multigram‐scale synthesis and the antiproliferative activity of a series of diiron cyclopentadienyl complexes containing bridging vinyliminium ligands. IC50 values in the low‐to‐mid micromolar range were determined against cisplatin sensitive and resistant human ovarian carcinoma (A2780 and A2780cisR) cell lines. Notable selectivity towards the cancerous cells lines compared to the non‐tumoral human embryonic kidney (HEK‐293) cell line was observed for selected compounds. The activity seems to be multimodal, involving reactive oxygen species (ROS) generation and, in some cases, a fragmentation process to afford monoiron derivatives. The large structural variability, amphiphilic character and good stability in aqueous media of the diiron vinyliminium complexes provide favorable properties compared to other widely studied classes of iron‐based anticancer candidates.

The synthesis and characterization of hitherto hypothetical AuIII π‐alkyne complexes is reported. Bonding and stability depend strongly on the trans effect and steric factors. Bonding characteristics shed light on the reasons for the very different stabilities between the classical alkyne complexes of PtII and their drastically more reactive AuIII congeners. Lack of back‐bonding facilitates alkyne slippage, which is energetically less costly for gold than for platinum and explains the propensity of gold to facilitate C−C bond formation. Cycloaddition followed by aryl migration and reductive deprotonation is presented as a new reaction sequence in gold chemistry.

A series of diiron complexes based on the [Fe2Cp2(CO) x ] skeleton (Cp = η5-C5H5, x = 2, 3; η4-C5H5Ph in place of one Cp in one case) and containing different bridging hydrocarbyl ligands (aminocarbyne, thiocarbyne, allenyl) were preliminarily investigated for their anticancer potential. The water solubility, stability in water and in the presence of a cell culture medium, and octanol/water partition coefficient were evaluated by spectroscopic techniques. The cytotoxicity was assessed in vitro toward the human ovarian carcinoma cell line A2780, the human triple negative breast cancer cell line MDA-MB-231, and the human vascular smooth muscle cell line SMC. Some aminocarbyne complexes exhibited a potent cytotoxicity, with IC50 values in the low micromolar/nanomolar range, and a strong selectivity for the A2780 cells in comparison to the SMC cell line. Several experiments were carried out in order to give insight into the mode of action of selected compounds, including an assessment of catalytic NADH oxidation and ROS production and studies of binding with DNA and with a model protein.