Selenophilicity, minimized dihedral angles, acidic selenols, multitarget hopping: cytosolic delivery with 1,2-diselenolanes outperforms 1,2-dithiolanes, by far.

Diiron diselenolato complexes have been prepared as models of the active site of [FeFe]-hydrogenases. Treatment of Fe 3 (CO) 12 with 1 equiv of 1,3-diselenocyanatopropane (1) in THF at reflux afforded the model compound Fe 2 (µ-Se 2 C 3 H 6 )(CO) 6 (2) in 68% yield. The analogous methyl-substituted complex, Fe 2 (µ-Se 2 C 3 H 5 CH 3 )(CO) 6 (3), was obtained from the reaction of Fe 3 (CO) 12 with the in situ generated compound 3-methyl-1,2-diselenolane (4). In contrast, the reaction of Fe 3 (CO) 12 with 1,3,5-triselenacyclohexane (5) produced a mixture of Fe 2 (µ 2 ,κ-Se,C-SeCH 2 SeCH 2 )(CO) 6 (6), Fe 2 [(µ-SeCH 2 ) 2 Se](CO) 6 (7), and Fe 2 (µ-Se 2 CH 2 )(CO) 6 (8). Compounds 2, 3, 6, and 7 were characterized by IR, 1 H, 13 C, and 77 Se NMR spectroscopy, mass spectrometry, elemental analysis, and X-ray single-crystal structure analysis. The He I and He II photoelectron spectra for 3 are reported, and the electronic structure is further analyzed with the aid of DFT computations. The calculated reorganization energy of the cation of 3 to the "rotated" structure, which has a semibridging carbonyl ligand, is less than that of the analogous complexes with sulfur instead of selenium. Complexes 2 and 3 have been proved to be catalysts for electrochemical reduction of protons from the weak acids pivalic and acetic acid, respectively, to give hydrogen.

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Keywords: Iron / Cluster compounds / S ligands / Hydrogenase / Electrocatalysis / DihydrogenThe reactions of 1,2,4-trithiolane (1), 1,2,5-trithiepane (6), 1,2,5-trithiocane (12) and 1,2,6-trithionane (10) with nonacarbonyldiiron (2) have been investigated. A novel diiron model complex, which can serve as a model complex of the active site of [Fe-only]-hydrogenase, was formed from the reaction with 1. In contrast, the reaction of 6 with 2 afforded the trinuclear iron cluster 7. Interestingly, the diiron compound 11 was obtained with 1,2,6-trithionane (10), which can be attributed to the more flexible dithiolato ligand 10. Furthermore, the reaction with 1,2,5-trithiocane (12) yielded the trinuclear

Cisplatin and its analogues are first-line chemotherapeutic agents for the treatment of numerous human cancers. A major inconvenience in their clinical use is their strong tendency to link to sulfur compounds, especially in kidney, ultimately leading to severe nephrotoxicity. To overcome this drawback we prepared a variety of platinum complexes with sulfur ligands and analyzed their biological profiles. Here, a series of six platinum(II) compounds bearing a conserved O,S binding moiety have been synthesized and characterized as experimental anticancer agents. The six compounds differ in the nature of the O,S bidentate β-hydroxydithiocinnamic alkyl ester ligand where both the substituents on the aromatic ring and the length of the alkyl chain may be varied. The two remaining coordination positions at the square-planar platinum(II) center are occupied by a chloride ion and a DMSO molecule. These novel platinum compounds showed an acceptable solubility profile in mixed DMSO-buffer solutions and an appreciable stability at physiological pH as judged from analysis of their time-course UV-visible absorption spectra. Their anti-proliferative and pro-apoptotic activities were tested against the cisplatin-resistant lung cancer cell line A549. Assays revealed significant effects of the sample drugs at low concentrations (in the μmolar range); initial structure-activity-relationships are proposed. The activity of the apoptosis-promoting protein caspase 3/7 was determined; results proved that these novel platinum compounds, under the chosen experimental conditions, preferentially induce apoptosis over necrosis. Reactions with the model proteins cytochrome c, lysozyme and albumin were studied by ESI MS and ICP-OES to gain preliminary mechanistic information. The tested compounds turned out to metalate the mentioned proteins to a large extent. In view of the obtained results these novel platinum complexes qualify themselves as promising cytotoxic agents and merit, in our opinion, a deeper pharmacological evaluation as prospective anticancer agents.

In order to elucidate the influence of the bridging chalcogen atoms in hydrogenase model complexes, diiron dithiolato, diselenolato, and ditellurolato complexes have been prepared and characterized. Treatment of Fe3(CO)12 with 3,3-bis(thiocyanatomethyl)oxetane (1) or a mixture of 2-oxa-6,7-dithiaspiro[3.4]octane (2a) and 2-oxa-6,7,8-trithiaspiro[3.5]nonane (2b) in toluene at reflux afforded the model compound Fe2(μ-S2C5H8O)(CO)6 (3). The analogous diselenolato and ditellurolato complexes, Fe2(μ-Se2C5H8O)(CO)6 (4) and Fe2(μ-Te2C5H8O)(CO)6 (5), were obtained from the reaction of Fe3(CO)12 with 2-oxa-6,7-diselenaspiro[3.4]octane (6) and 2-oxa-6,7-ditelluraspiro[3.4]octane (7), respectively. Compounds 3−5 were characterized by spectroscopic techniques (NMR, IR, photoelectron spectroscopy), mass spectrometry, single-crystal X-ray analysis, and computational modeling. The electrochemical properties for the new compounds have been studied to assess their ability to catalyze electrochemical reduction of protons to give dihydrogen, and the catalytic rate is found to decrease on going from the sulfur to selenium to tellurium compounds. In the series 3−5 the reorganization energy on going to the corresponding cation decreased from 3 to 4 to 5. Spectroscopic and computational analysis suggests that the increasing size of the chalcogen atoms from S to Se to Te increases the Fe−Fe distance and decreases the ability of the complex to form the structure with a rotated Fe(CO)3 group that has a bridging carbonyl ligand and a vacant coordination site for protonation. This effect is mirrored on reduction of 3−5 in that the rotated structure with a bridging carbonyl, which creates a vacant coordination site for protonation, is disfavored on going from the S to Se to Te complexes.

A series of multifunctional (mercaptomethyl)silanes of the general formula type R(n)Si(CH(2)SH)(4-n) (n = 0-2; R = organyl) was synthesized, starting from the corresponding (chloromethyl)silanes. They were used as multidentate ligands for the conversion of dodecacarbonyltriiron, Fe(3)(CO)(12), into iron carbonyl complexes in which the deprotonated (mercaptomethyl)silanes act as μ-bridging ligands. These complexes can be regarded as models for the [FeFe] hydrogenase. They were characterized by elemental analyses (C, H, S), NMR spectroscopic studies ((1)H, (13)C, (29)Si), and single-crystal X-ray diffraction. Their electrochemical properties were investigated by cyclic voltammetry to disclose a new mechanism for the formation of dihydrogen catalyzed by these compounds, whereby one sulfur atom was protonated in the catalytic cycle. The reaction of the tridentate ligand MeSi(CH(2)SH)(3) with Fe(3)(CO)(12) yielded a tetranuclear cluster compound. A detailed investigation by X-ray diffraction, electrochemical, Raman, Mössbauer, and susceptibility techniques indicates that for this compound initially [Fe(2){μ-MeSi(CH(2)S)(2)CH(2)SH}(CO)(6)] is formed. This dinuclear complex, however, is slowly transformed into the tetranuclear species [Fe(4){μ-MeSi(CH(2)S)(3)}(2)(CO)(8)].

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