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Consequence of polystyrene particles size and concentration in plant tissues contamination.

Prebiotic chemistry was likely mediated by metals, but how such prebiotic chemistry progressed into the metabolic-like networks needed to sustain life remains unclear. Here we experimentally delineate a potential path from prebiotically plausible iron–sulfur peptide catalysts to the types of pH gradients exploited by all known living organisms. Iron–sulfur peptides cooperatively accept electrons from NADH in a manner that is only partially mediated by ionic interactions. The electrons are then either passed to a terminal electron acceptor, such as hydrogen peroxide, or to an intermediate carrier, such as ubiquinone. The reduction of hydrogen peroxide leads to the production of hydroxide, which then contributes to the formation of a pH gradient across late protocell membranes. The data are consistent with the activity of prebiotic iron–sulfur peptide catalysts providing a selective advantage by equipping protocells with a pathway that connects catabolism to anabolism.

The methyl sulfide derivatives of cobalt bis(dicarbollide) [8,8'-(MeS)2-3,3'-Co(1,2-C2B9H10)2]-, [4,4'-(MeS)2-3,3'-Co(1,2-C2B9H10)2]- and [4,7'-(MeS)2-3,3'-Co(1,2-C2B9H10)2]- were synthesized by the reaction of CoCl2 with [10-MeS-7,8-C2B9H11]- and [9-MeS-7,8-C2B9H11]-, respectively, in strong alkaline aqueous media. The 4,4'-(rac)- and 4,7'-(meso)-isomers were separated by column chromatography on silica as the tetrabutylammonium salts. The structures of (Bu4N)[8,8'-(MeS)2-3,3'-Co(1,2-C2B9H10)2], (Bu4N)[4,4'-(MeS)2-3,3'-Co(1,2-C2B9H10)2] and (Bu4N)[4,7'-(MeS)2-3,3'-Co(1,2-C2B9H10)2] were determined by single crystal X-ray diffraction. In the solid state, the rotation of the two dicarbollide ligands with respect to each other is hampered due to formation of intramolecular CHcarb ***S(Me) hydrogen bonds between the ligands, that results in stabilization of definite rotamers - transoid- in the case of 8,8'-isomer, and gauche- in the case of 4,4'- and 4,7'-isomers. These data are in a good agreement with results of the quantum chemical calculations.

Demethylation of cyclohexadienyl complexes (η-X-SMe2-7,8-C2B9H10)Fe(η5-C6H7) (1a,b; X = 9 (a), 10 (b), where X is number of the substituent position) with PhCH2SNa in DMF (dimethylformamide) and subsequent protonation by acetic acid lead to iron benzene complexes (η-X-SMe-7,8-C2B9H10)Fe(η-C6H6) (2a,b). Visible light irradiation of 2a in the presence of tBuNC or Cp*Fe(η-cyclo-P5) affords neutral half-sandwich (η-9-SMe-7,8-C2B9H10)Fe(tBuNC)3 (3) or triple-decker (η-9-SMe-7,8-C2B9H10)Fe(μ-η:η-cyclo-P5)FeCp* (4) complexes. Reaction of 2b with (THF)W(CO)5 selectively gives the iron-tungsten dinuclear complex (η-10-SMe(W(CO)5)-7,8-C2B9H10)Fe(η-C6H6) (5). Structures of 2a, 4 and 5 were determined by X-ray diffraction. Electrochemistry reveals that the redox processes of the SMe-substituted ferracarboranes are cathodically shifted (by 350 mV) with respect to the corresponding redox changes of the SMe2-analogs. The Fe-C6H6 bonding in 2a and the related benzene complexes [(η-9-SMe2-7,8-C2B9H10)Fe(η-C6H6)]+ and (η-7,8-C2B9H10)Fe(η-C6H6) was analyzed by energy decomposition analysis.

This study was aimed at evaluating in vitro the effects of a 75% v/v ethanolic extract of leaves of Castanea sativa Mill. (var. Bastarda Rossa, Mount Amiata, Tuscany, Italy) on ejaculated human sperm. Total polyphenols and total flavonoids contained in the extract were determined by a colorimetric assay and HPLC-DAD. The DPPH test and electrochemistry were utilized to study the antioxidant activity of the extract. Swim-up-selected sperm from 8 healthy men were treated with the C. sativa leaf extract at different dilutions (1 : 100, 1 : 200, and 1 : 500), and sperm motility was assessed following the WHO guidelines. Swim-up-selected spermatozoa were incubated with 100 μM H2O2 to induce lipid peroxidation (LPO) and with H2O2 and the leaf extract (1 : 100, 1 : 200, and 1 : 500) to test the antioxidant activity of the extract. The levels of LPO were determined by measuring malondialdehyde (MDA) concentrations. The treated samples were also analyzed by transmission electron microscopy (TEM) for ultrastructural evaluation. The chemical analysis showed that one-third ca. of the polyphenols in the C. sativa extract were made up of flavonoids, with hyperoside present in high concentration. A good antioxidant activity was demonstrated by both the DPPH test and electrochemical analysis. The C. sativa leaf extract did not decrease sperm motility at all tested dilutions. Treatment with H2O2 alone caused a significant increment in MDA levels (P = 0.006993), while the treatment with H2O2 plus C. sativa extract diluted to 1 : 100 and 1 : 200 significantly reduced MDA levels (P = 0.01476 and P = 0.01571, respectively), with respect to H2O2 alone. TEM analysis confirmed the protective effect of the extract on damage induced by LPO, in particular that occurring at the plasma membrane level. The C. sativa leaf extract could be used in human and farm animal protocols for gamete handling, such as techniques of assisted reproduction and cryopreservation of semen, all conditions in which oxidative stress is exacerbated.

The reaction of the bromide complexes [CpCo(μ-1,3-C3B2Me5)MBr2]2 [M = Rh (1), Ir (2); Cp = cyclopentadienyl] with AgBF4 in acetonitrile affords the tris(acetonitrile) μ-diborolyl triple-decker complexes [CpCo(μ-1,3-C3B2Me5)M(MeCN)3]2+ [Rh (3), Ir (4)]. The labile nitromethane solvates [CpCo(μ-1,3-C3B2Me5)M(MeNO2)3]2+, generated in a similar way, react with benzene and its methylated derivatives to give the arene triple-decker complexes [CpCo(μ-1,3-C3B2Me5)M(arene)]2+ [M = Rh (5), Ir (6); arene = C6H6 (a), 1,2,4,5-Me4C6H2 (b), C6Me6 (c)]. The structures of 5b(BF4)2, 5c(BF4)2, 6b(BF4)2 and 6c(BF4)2 were determined by X-ray diffraction. The electron-transfer ability of the arene complexes was ascertained by electrochemical techniques. In general, they are able to undergo two separate one-electron reductions reversibly. DFT calculations revealed structural changes caused by redox processes and satisfactorily predicted the redox potentials. The second reduction is accompanied by a η6 η4 hapticity change of the arene ligand. Energy decomposition analysis revealed that the Rh–benzene bond in cation 5a is weaker than in cyclopentadienyl analogues [(C5R5)Rh(C6H6)]2+; however, 5a proved to be the least reactive in benzene replacement with acetonitrile and mesitylene.

The electrophilic insertion of organometallic species into metallacarboranes was studied in detail for the model compound - the 12-vertex closo-ruthenacarborane anion [Cp*Ru(C2B9H11)]- (1). Reactions of the anion 1 with the 12-electron cationic species [M(ring)]+ (M(ring) = RuCp, RuCp* and Co(C4Me4)) gave the 13-vertex closo-dimetallacarboranes Cp*Ru(C2B9H11)M(ring). Similar reactions of the neutral ruthenacarborane Cp*Ru(Me2S-C2B9H10) produce the cationic dimetallacarboranes [Cp*Ru(Me2S-C2B9H10)M(ring)]+. The symmetrical 13-vertex diruthenacarboranes (C5R5)Ru(R2C2B9H9)Ru(C5R5) can be prepared by the direct reactions of Tl2[7,8-R2-7,8-C2B9H9] (R = H and Me) with two equivalents of [CpRu(MeCN)3]+ or [Cp*RuCl]4. The insertions of the 14-electron cationic species [M(ring)]+ (M(ring) = NiCp, NiCp* and Co(C6Me6)) into 1 gave the 13-vertex dimetallacarboranes Cp*Ru(C2B9H11)M(ring), which have a distorted framework with one open face. The structures of Cp*Ru(C2B9H11)Co(C4Me4) and Cp*Ru(C2B9H11)NiCp were established by X-ray diffraction. Some of the 13-vertex dimetallacarboranes have two electrons less than required by Wade's rules. This violation is explained by the absence of the appropriate pathway for the distortion of the framework.

The first derivative of the methylium cation with the triple-decker substituent, [CpCo(C

Metallacarboranes 3-(η-C5R5)-3,1,2-MC2B9H11 (1a: M = Co, R = H; 1b: M = Co, R = Me; 2a: M = Rh, R = H; 2b: M = Rh, R = Me; 3a: M = Ir, R = H; 3b: M = Ir, R = Me) were obtained by reactions of Tl[Tl(η-7,8-C2B9H11)] with [(η-C5R5)MX2]2 (X = Cl, I) or [CpM(MeCN)3]2+. The structures of 2a and 3a were determined by X-ray diffraction. The electrochemical investigation of complexes 2a,b and 3a,b shows that they undergo the partially reversible M(III)/M(II) electron addition followed by the irreversible M(II)/M(I) reduction. Such a path is quite reminiscent of that occurring for the isolobal and isoelectronic monocations [(η-C5R5)MCp]+ (M = Rh, Ir; R = H, Me). An electrochemical comparison is made also with respect to the cobalt derivatives 1a,b. DFT calculations of the redox potentials and the respective geometrical changes were performed. Metal–ligand bonding in 1a, 2a and 3a was analyzed by energy decomposition analysis.

Cationic triple-decker complexes with a bridging diborolyl ligand, [CpCo(μ-1,3-C3B2Me5)M(ring)]+ (M(ring) = CoCp (2a), CoCp* (2b), RhCp (3a), RhCp* (3b), IrCp (4a), IrCp* (4b), Ru(C6H6) (5a), Ru(p-MeC6H4Pri) (5b), Ru(C6Me6) (5c), Ru(η6-cycloheptatriene) (6)), were synthesized by reaction of CpCo(μ-1,3-C3B2Me5)Tl with [M(ring)Hal2]2. The structures of 2aBPh4, 2bPF6, 4aPF6, 5aOTf, and 5cPF6 were determined by X-ray diffraction. The electron-transfer ability of the complexes has been ascertained by electrochemical and spectroelectrochemical techniques. In general, they are able to shuttle reversibly in the sequence 2+/+/0/–, plausibly affording completely delocalized mixed-valence derivatives. DFT calculations revealed structural changes accompanying redox processes and satisfactorily predicted the potentials for the first reduction and first oxidation.

Within a couple of years we have planned to systematically update structure/electrochemistry of the different classes of metalloproteins harboring iron–sulfur clusters. In this picture we have so far dealt with {Fe(Cys) 4 }, {[Fe 2 S 2 ](Cys) 4 }, {[Fe 2 S 2 ](Cys) 3 (X)} (X = Asp, Arg, His), {[Fe 2 S 2 ](Cys) 2 (His) 2 }, {[Fe 3 S 4 ](Cys) 3 }, and {[Fe 4 S 4 ](Cys) 4 } cores. Since a significant number of structurally characterized [4Fe–4S] proteins harbor {[Fe 4 S 4 ](S γ Cys ) 3 (nonthiolate ligand)} iron–sulfur centers, the aim of the present review paper is to complement our paper review on {[Fe 4 S 4 ](Cys) 4 } cores with structure and electrochemistry of {[Fe 4 S 4 ](S γ Cys ) 3 (nonthiolate ligand)} proteins in order to gain a panoramic overview of the state-of-the-art of structure/electrochemistry of all the [4Fe–4S] proteins (excluding obviously those proteins which harbor mixed iron–sulfur clusters such as [4Fe–4S] + [2Fe–2S], [4Fe–4S] + [3Fe–4S], [4Fe–4S] + [3Fe–4S] + [2Fe–2S], and [4Fe–4S] + [3Fe–4S] + [4Fe–3S]).

Triple-decker complexes with a bridging diborolyl ligand CpCo(μ-1,3-C3B2Me5)M(ring) (M(ring) = RuCp, 4; RuCp*, 5; Co(C4Me4), 6) were synthesized by electrophilic stacking of the sandwich anion [CpCo(1,3-C3B2Me5)]− with the [(ring)M(MeCN)3]+ cations. Structures of 4−6 were confirmed by X-ray diffraction. The electrochemical and spectroelectrochemical behavior of the complexes prepared was studied. DFT calculations of the redox potentials were also performed. Similar bonding properties of anions [CpCo(1,3-C3B2R5)]− and [C5R5]− (R = H, Me) toward [M(ring)]+ cations were established both experimentally (synthesis, electrochemistry, and X-ray diffraction) and theoretically (energy decomposition and Mulliken population analysis).

A novel "Keppler type" ruthenium(III) compound trans-[bis(2-amino 5-methylthiazole)tetrachlororuthenate(III)] 1, of potential interest as an anticancer agent, was designed, synthesized, and characterized. Its interactions with various proteins were analyzed, including the selenoenzyme thioredoxin reductase, an emerging target for anticancer metallodrugs. The selective inhibition of the cytosolic form of this selenoenzyme was documented, this being the first report of significant thioredoxin reductase inhibition by a ruthenium compound.

Reaction of the phosphadicarbollide anion [7,8,9-PC2B8H10]– (4) with [CpFe(C6H6)]+ or [Cp*Fe(MeCN)3]+ gives the expected 12-vertex ferraphosphadicarbollides [1-C5R5-1,2,3,4-FePC2B8H10] [R = H (5a), Me (5b); the metal atom is assigned number 1] in around 35 % yield. Compounds 5a,b undergo selective polyhedral rearrangement at 150 °C to give the corresponding isomers [1-C5R5-1,2,4,5-FePC2B8H10] (6a,b). The structure of 5a has been determined by X-ray diffraction. An electrochemical investigation has revealed that all the compounds obtained display the FeII/FeIII oxidation process with features of chemical reversibility on the cyclic voltammetric timescale. However, only cation [6b]+ is reasonably stable on the long timescales of electrolysis. Ferraphospadicarbollides 5a and 6a are more difficult to oxidize than the related dicarbollide and tricarbollide derivatives [CpFe(C2B9H11)]–and [CpFe(C3B8H11)], respectively. Temperature-dependent Mossbauer effect studies show that the recoil-free fraction over the temperature interval 110–342 K for 5a is well accounted for by a linear regression, and a calculation of the root-mean-square-amplitude-of-vibration (rmsav) of the iron atom, based on the Mossbauer effect (ME) data, is in reasonable agreement with the value calculated from the single-crystal X-ray study at 120 K. Similarly, the ME and X-ray rmsav data for 6a at 293 K are in excellent agreement with each other, and the value at 120 K calculated for 6a is in good agreement with that observed for 5a. The metal atom motion is nearly isotropic with respect to the major symmetry axis running through the Cp ring and the Fe atom. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Metallacarboranes as electrochemical labels are proposed. The electrochemical properties of nucleoside conjugates, derivatives of thymidine (T), 2′-deoxycytidine (dC), 2′-deoxyadenosine (dA) and 2′-deoxyguanosine (dG), containing metallacarborane complex of cobalt or iron are described. A multielectrochemical detection using specific metallacarborane tags is shown. The proposed labelling of nucleosides lays the foundations for electrochemical coding of DNA with metallacarborane complexes and simultaneous detection of several DNA targets. Keywords: Metallacarboranes, Nucleosides, DNA labelling, Electrochemical detection

The reduction behavior of the isoelectronic complexes [CpMIII(η6-C6R6)]2+ (M=Rh, Ir; R=H, Me) and [(η-9-SMe2-7,8-C2B9H10)MIII(η6-C6R6)]2+ (M=Rh, Ir; C6R6 = C6H6, C6H5OMe, C6H3Me3) has been studied by cyclic voltammetry and controlled potential coulometry in acetonitrile and propylene carbonate at 253 and 298 K, respectively. The extent of chemical reversibility of the pertinent sequences Rh(III)/Rh(II)/Rh(I) and Ir(III)/Ir(I) is highly dependent on both the nature of the solvent and the intrinsic electronic properties of the arene substituents. The arene η6 coordination makes the derivatives in their lower oxidation states notably short lived, even if, in some cases, the use of propylene carbonate improves their stability or causes the increase in their lifetimes before changing the arene coordination from η6 to η4. Cations [(η-9-SMe2-7,8-C2B9H10)M(η6-C6R6)]2+ were obtained by the bromide abstraction from [(η-9-SMe2-7,8-C2B9H10)MBr2]2 with Ag+ in the presence of benzene and its derivatives. The structure of [(η-9-SMe2-7,8-C2B9H10)Ir(η6-C6H5OMe)](BF4)2 was determined by X-ray diffraction.

Metallacarboranes containing carborane ligands possessing a pentagonal open face can coordinate metal atoms in a η5-manner quite similar to the cyclopentadienyl monoanion, thus affording metallocene analogues. By virtue of such an analogy, their electron transfer aptitude plays an important role in their physico-chemical characterisation. We review such an aspect, also providing evidence for the structural consequences of their electron transfer processes. At variance with metallocenes, electrochemical investigations on the metallacarboranes have not yet become a routine tool to search for their potential application in fields which require electronic mobility.

Reactions of the 11-vertex phosphadicarbollide anions [10-R-7,8,9-PC2B8H9]- (R = H (1a) and Cl (1b)) and [9-Cl-7,8,11-PC2B8H9]- (7) with [Cb*Co(MeCN)3]PF6 or [Cb*Co(C6H6)]PF6 (Cb* = C4Me4) give the...

The reaction of RhCl3 · 3H2O with SbPh3 (Ph, C6H5) in ethanol produced mer-[RhCl3(SbPh3)3] (1), as the main product, together with trans-[RhCl2(Ph)(SbPh3)3] (2) (R. Cini, G. Giorgi, L. Pasquini, Inorg. Chim. Acta 196 (1992) 7; A. Cavaglioni, R. Cini, J. Chem. Soc., Dalton Trans. (1997) 1149). Ways to improve the yield for 1 and 2 were a subject of further works by this laboratory during the past decade and the reactivity of the organometallic compound 2 was investigated towards a variety of bases. Long sought single crystals of 1 suitable for X-ray diffraction have been obtained from hot acetone solution. The metal centre has a pseudo-octahedral coordination environment with the three chloride anions and the three SbPh3 molecules in mer positions. The Rh–Cl bond trans to Sb is significantly weakened by the high trans influence by antimony itself. This gives the rationale for the formation of 2 from RhCl3 and SbPh3 via the preliminary formation of 1, followed by dissociation of the activated chloride anion, and the subsequent formation of the Rh–C(Ph) linkage. The reaction of 1 with 2-thio-1,3-pyrimidine (Htpym) in ethanol produces crystalline [Rh( N 1, S 2-tpym)2( N 1(Sb), S 2(Rh)-tpym)(SbPh3)] (3). Single crystals suitable for X-ray diffraction studies as obtained from ethanol/diethyl-ether contain a complex molecule and a quarter of an ethanol molecule in the asymmetric unit. Two out of three tpym− anions chelate the metal centre via the N1 and S2 atoms, whereas the third tpym− anion behaves as mono-dentate through the S2 atom only. The sixth co-ordination position is occupied by the Sb atom. Interestingly, one of the N atoms of the monodentate tpym− anion behaves as electron donor to Sb and a Sb–N linkage forms (d(Sb–N), 2.846 A). As a consequence, an unusual totally hetero-atomic five-membered co-ordination ring of the type RhSCNSb(Rh) forms. A molecular modelling analysis at the hybrid density functional level DFT-B3LYP was performed on selected co-ordination molecules.

Gold(III) compounds are emerging as a new class of metal complexes with outstanding cytotoxic properties and are presently being evaluated as potential antitumor agents. We report here on the solution and electrochemical properties, and the biological behavior of some gold(III) dithiocarbamate derivatives which have been recently proved to be one to 4 orders of magnitude more cytotoxic in vitro than the reference drug (cisplatin) and to be able to overcome to a large extent both intrinsic and acquired resistance to cisplatin itself. Their solution properties have been monitored in order to study their stability under physiological conditions; remarkably, they have shown to undergo complete hydrolysis within 1 h, the metal center remaining in the +3 oxidation state. Their DNA binding properties and ability in hemolyzing red blood cells have been also evaluated. These gold(III) complexes show high reactivity toward some biologically important isolated macromolecules, resulting in a dramatic inhibition of both DNA and RNA synthesis and inducing DNA lesions with a faster kinetics than cisplatin. Nevertheless, they also induce a strong and fast hemolytic effect (compared to cisplatin), suggesting that intracellular DNA might not represent their primary or exclusive biological target.

nido-Carborane 9-NMe3-7,8-C2B9H11 (2c) was synthesized by CuSO4 oxidation of anion [7,8-C2B9H12]− in the presence of [Me3NH]+ in aqueous ammonia. Improved procedures for the preparation of nido-carboranes 9-SMe2-7,8-R2-7,8-C2B9H9 (2a: R = H; 2b: R = Me) and 9-py-7,8-C2B9H11 (2d) were developed. nido-Carborane monoanions [9-L-7,8-R2-7,8-C2B9H8]− (1a–1d), generated by deprotonation of 2a–2d by NaH, react with Cb*Co(CO)2I or [Cb*Co(MeCN)3]+ (Cb* = C4Me4) to give complexes Cb*Co(η-9-L-7,8-R2-7,8-C2B9H8) (3a–3d). The structures of carborane 2d and complexes 3a and 3d were determined by X-ray diffraction. Electrochemistry of the cobalt complexes was studied.

Tetramethylcyclobutadiene(cyclopentadienyl)cobalt complexes Cb*Co(C5H4R) (Cb* = η4-C4Me4; R = H (5a), Me (5b), SiMe3 (5d), C(O)H (5f), and C(O)Me (5g)) were obtained by reaction of cyclopentadienide anions either with the (carbonyl)iodide complex Cb*Co(CO)2I (1) (method A) or with the more reactive acetonitrile complex [Cb*Co(MeCN)3]+ (2) (method B). Analogous compounds Cb*CoCp* (5c), Cb*Co(1,3-C5H3(SiMe3)2) (5e), and Cb*Co(η5-indenyl) (6) can be prepared only by method B. Treatment of 5f,g with NaBH4/AlCl3 or LiAlH4 affords the alkyl derivatives 5b and 5h (R = Et) or the alcohols 5i (R = CH2OH) and 5j (R = CH(OH)Me), respectively. The reaction of 1 with fluorene/AlCl3 yields complex [Cb*Co(η6-fluorene)]+ (8), which was deprotonated by KOBut to give Cb*Co(η6-fluorenyl) (9). Visible light irradiation of 9 induces η6→η5 haptotropic rearrangement to afford Cb*Co(η5-fluorenyl) (7). The pyrrolyl and phospholyl complexes Cb*Co(C4R4N) (R = H (10a), Me (10c)) and Cb*Co(C4R4P) (R = H (11a), Me (11c); R4 = H2Me2 (1...

Two ruthenium(III) complexes bearing the thiazole ligand, namely, thiazolium (bisthiazole) tetrachlororuthenate (I, TzICR) and thiazolium (thiazole, DMSO) tetrachlororuthenate (II, TzNAMI) were prepared and characterized. The crystal structures of both complexes were solved by X-ray diffraction methods and found to match closely those of the corresponding imidazole complexes. The behavior in aqueous solution of bothTzICR and TzNAMI was analyzed spectroscopically. The time-dependent spectrophotometric profiles resemble closely those of the related ICR and NAMI-A anticancer compounds, respectively. It is observed that replacement of imidazole with thiazole, a less basic ligand, produces a significant decrease of the ligand exchange rates in the case of the NAMI-like compound. The main electrochemical features of these ruthenium(III) thiazole complexes were determined and compared to those of ICR and NAMI-A. Moreover, some preliminary data were obtained on their biological properties. Notably, both complexes exhibit higher reactivity toward serum albumin than toward calf thymus DNA; cytotoxicity is negligible in line with expectations. A more extensive characterization of the pharmacological properties in vivo is presently in progress.

The reaction of trans-[RuCl(2)(PPh(3))(3)] (Ph = C(6)H(5)) with 2-thio-1,3-pyrimidine (HTPYM) and 6-thiopurines (TPs) produced mainly crystalline solids that consist of cis,cis,trans-[Ru(PPh(3))(2)(N,S-TPYM)(2)] (1) and cis,cis,trans-[Ru(PPh(3))(2)(N(7),S-TPs)(2)]X(2) (X = Cl(-), CF(3)SO(3)(-)). In the case of TPs, other coordination isomers have never been isolated and reported. Instead, the mother liquor obtained after filtration of 1 produced red single crystals of trans,cis,cis-[Ru(PPh(3))(2)(N,S-TPYM)(2)].2H(3)O(+).2Cl(-) (2.2H(3)O(+).2Cl(-)). Selected ruthenium(II)-thiobase complexes were studied for their structural, reactivity, spectroscopic, redox, and cytotoxic properties. Single crystals of 1 contain thiopyrimidinato anions chelated to the metal center via N and S. The Ru[bond]N bonds are significantly elongated for 1 [2.122(2) and 2.167(2) A] with respect to 2 [2.063(3) A] because of the trans influence from PPh(3). The coordination pseudo-octahedron for 2 is significantly elongated at the apical sites (PPh(3) ligands). Solutions of cis,cis,trans isomers in air are stable for weeks, whereas those of 2 turn green within 24 h, in agreement with the respective redox potentials. cis,cis,trans- and trans,cis,cis-[Ru(PH(3))(2)(N,S-TPYM)(2)], as optimized through the DFT methods at the Becke3LYP level are in good agreement with experimental geometrical parameters (1 and 2), with cis,cis,trans being more stable than trans,cis,cis by 3.88 kcal. The trend is confirmed by molecular modeling based on semiempirical (ZINDO/1) and molecular mechanics (MM) methods. Cytotoxic activity measurements for cis,cis,trans-[Ru(PPh(3))(N-THZ)(N(7),S -H(2)TP)(2)]Cl(2) (4) (THZ = thiazole, H(2)TP = 6-thiopurine) and cis,cis,trans-[Ru(PPh(3))(2)(N(7),S-HTPR)2]Cl(2) (5) (HTPR = 6-thiopurine riboside) against ovarian cancer cells A2780/S gave IC(50) values of 17 +/- 1 and 29 +/- 9 microM, respectively. Furthermore, the spectral analysis of HTPYM, TPs, and their Ru(II) complexes in solution shows that intense absorptions occur in the UVA/vis region of light, whereas standard nucleobases absorb in the UVB region.

The parallel and perpendicular stacking of ferrocene rings in 1,8-bis-[1-(1′-phenylthio)ferrocenyl]naphthalene (1) and 8,8′-bis-[1-(1′-phenylthio)ferrocenyl]-1,1′-binaphthyl (2), respectively, were investigated. They were synthesized from the Suzuki coupling of 2,4,6-tris(1′-phenylthio-1-ferrocenyl)boroxin (3) with 1,8-diiodonaphthalene and 1,8-diiodo-1,1’-binaphthyl, respectively. Their structures were confirmed by single-crystal X-ray analyses. The two cyclopentadienyl (Cp) rings (C9C13 and C19C23) of the two respective ferrocenes Fe(1) and Fe(2) of 1 are not parallel, but are 21.3° away from parallel. The distance between the centroids of these two Cp rings is 3.336 A. The two Cp rings (C9C13 and C9′C13′) of the two respective ferrocenes Fe(1) and Fe(2) of 2 are not perpendicular, but have a dihedral angle of 49.9°, and the distance between two centroids of these two Cp rings is 5.255 A. The electrochemical behaviour of 1 and 2 in dichloromethane solution shows that they undergo reversibly two ferrocene-centred one-electron oxidations to the corresponding dications. The separation between the two anodic processes is greater for 1 with respect to 2, but the absolute value of the separation significantly depends upon the nature of the supporting electrolyte. In the presence of the classical [NBu4][PF6] the ΔE°′ value is 0.15 V for 1 and 0.07 V for 2. In the presence of the new [NBu4][B(C6F5)4] the ΔE°′ value increases to 0.45 V for 1 and 0.13 V for 2. In view of the low ion-pairing ability of the [B(C6F5)4]− counteranion, it is conceivable that the increased intramolecular electronic communication might essentially arise from the increased electrostatic repulsion (or through-space interaction) following the 0/+/2+ redox changes rather than from through-bond electron delocalization.

Triple-decker cationic complexes with a central pentaphospholyl (pentaphosphacyclopentadienyl) ligand [Cp*M(μ-η:η-P5)M′(η-C5R5)]+ (3b: M = M′ = Fe, R = Me; 4a: M = Ru, M′ = Fe, R = H; 4b: M = Fe, M′ = Ru, R = H; 4c: M = Fe, M′ = Ru, R = Me; 5a: M = M′ = Ru, R = H; 5b: M = M′ = Ru, R = Me) were synthesized by exploitation of the stacking reactions of pentaphosphametallocenes Cp*M(η-P5) (1: M = Fe; 2: M = Ru) with half-sandwich fragments [(η-C5R5)M′]+. They were isolated as salts with BF4− or PF6− anions, and the structures of 4aPF6 and 5bPF6 were determined by X-ray diffraction. Triple-decker complexes with a central pentaphospholyl ligand are less reactive in nucleophilic degradation reactions than analogous complexes with C4Me4P and Cp* ligands in the bridging position. Only 4a and the previously known analogue 3a (M = M′ = Fe, R = H), containing the CpFe fragment, are nucleophilically destroyed by MeCN and NaI. The electrochemical properties of 2, 3a, 3b, 4a−c, 5a and 5b and the related cobalt-containing complexes [(η-C4Me4)Co(μ-η:η-P5)MCp*]+ (6: M = Fe; 7: M = Ru) were investigated. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

The reaction of trans -[RuCl 2 (SbPh 3 ) 4 ] ( 1 ) (Ph=C 6 H 5 ) (Inorg. Chim. Acta 208 (1993) 189) with tenfold excess N -methylimidazole (Meim) and 4-methylpyrimidine (Mepym) in chloroform at reflux under ultrapure nitrogen produced trans , cis , cis -[RuCl 2 (Meim) 2 (SbPh 3 ) 2 ] ( 2 ), and trans , cis , cis -[RuCl 2 (Mepym) 2 (SbPh 3 ) 2 ] ( 3 ), respectively. The compounds were purified and crystallized from ethylacetate and absolute ethanol and gave single crystals of 2 ·CH 3 COOCH 2 CH 3 and 3 , respectively. The X-ray diffraction analyses showed that for both 2 and 3 the ligand substitutions on 1 , takes place in cis -positions. The relative orientation of the two Meim and Mepym ligands around the RuN vectors is head-to-head and head-to-tail for 2 and 3 , respectively, in the solid state, whereas free rotation was detected in solution (CDCl 3 ) at 25 °C. The RuN bond distances average 2.108(4) A, 2 , and 2.131(5) A, 3 , and are elongated by the trans influence and by the steric hindrance from the two SbPh 3 ligands. Intramolecular attractive stacking interactions between one of the phenyl rings and one of the Meim or Mepym ligands in 2 and 3 , attenuate the repulsive steric hindrance within the coordination sphere. The RuNC bond angles for 2 differ by 5.2° but have the opposite trend for the two Meim ligands. This fact agrees with a small energy barrier for the in plane swinging of the Meim ring with respect to the RuN line and is related to the CH⋯Cl intramolecular interactions. Both the Mepym ligands of 3 have intermolecular interactions of the type CH⋯N (N⋯C, 3.63(1) A), the two “paired bases” not being coplanar (dihedral angle, 46.5(3)°). A density functional and ab initio optimization analysis at the Becke3LYP/6-31G** level and CCSD(T)/6-31G** level, carried out on the Pym molecule and on the Pym⋯Pym adduct, confirmed the feasibility of the CH⋯N interaction at least for an environment that is not aqueous and allowed computation of a pairing energy of −11.657 and −13.887 kJ mol −1 , respectively. Structure optimization analyses were also performed on the model molecules, trans -[RuCl 2 (SbH 3 ) 4 ] at the Becke3LYP/LANL2DZ (6-31G**, Cl, H) level, and head-to-head and head-to-tail trans , cis , cis -[RuCl 2 (Im) 2 (SbH 3 ) 2 ], head-to-head and head-to-tail trans , trans , trans -[RuCl 2 (Im) 2 (SbH 3 ) 2 ], head-to-tail trans , cis , cis and trans , trans , trans -[RuCl 2 (Im) 2 (PH 3 ) 2 ] at the Becke3LYP/LANL2DZ level. The difference between the electronic energies relevant to the two couples of isomers head-to-head and head-to-tail trans , cis , cis -[RuCl 2 (Im) 2 (SbH 3 ) 2 ] and trans , trans , trans -[RuCl 2 (Im) 2 (SbH 3 ) 2 ] is no larger than 2.7 kJ mol −1 , showing that inter- and intramolecular weak forces play a significant role in discriminating the most stable isomer, at the solid state. A planar model molecule of the type [Ru(Im)] 2+ was fully optimized at the Becke3LYP/LANL2DZ level. The computed RuN(1)C(2) bond angle is 126.3° and the computed energy required to bend the angle in plane in the range 118.0–134.0° is less than 5.0 kJ mol −1 . This confirms that weak interactions like CH⋯Cl can reasonably cause significant changes at the level of the RuNC bending in plane for metal–imidazole complexes. In dichloromethane solution complex 2 displays a chemically reversible Ru(II)/Ru(III) oxidation with formal electrode potentials of −0.27 V (versus the ferrocene/ferricinium couple), whereas 3 , trans , trans , trans -[RuCl 2 (Mepym) 2 (PPh 3 ) 2 ] ( 5 ) and trans , trans , trans -[RuCl 2 (Thz) 2 (PPh 3 ) 2 ] ( 6 ) (Thz, 1,3-thiazole) undergo the same type of oxidation process with electrode potential values +0.08, +0.07 and −0.06 V, respectively. Therefore, 2 looks like the more suitable for protein binding (after oxidation to the mono-cation), when compared to 3 , 5 , and 6 , a step believed to be important for decreasing the toxicity of ruthenium based anticancer drugs.

The redox chemistry of aryl alcohols, or phenols, is of great interest because of their involvement in important biological and industrial processes. Phenol and its substituted analogs are facile one-electron reducing agents that are often involved in electrochemical, photochemical and radiation chemical electron transfer reactions. For these and many other reasons the interest of chemists in the metal phenolates has always been lively and a huge number of these complexes are known. In this chapter we describe the redox behavior of the more restricted set of homoleptic aryloxide complexes. The peculiarities of phenolates as ligands make them usually unable to stabilize a metal in different redox states and, very often, reduction of the metal is accompanied by the release of one or more of the ligands and/or by the formation of polynuclear compounds. This may give rise to a complicated pattern in the redox chemistry of these complexes, but may also open the way to a rich, redox-driven, chemistry of this class of compounds, which, apparently, is still largely unexplored. Keywords: electrochemistry; cyclic voltammetry; redox chemistry; aryloxide complexes; aryl alcohols; homoleptic metal phenolates

The reaction of [RhCl2(Ph)(PPh3)2] with purine-6-thione (H2tp) in alcohol produced the title compound which consists of aggregates of [Rh(C6H5)(H1,H9-H2tp)2(PPh3)]2+ and [Rh(C6H5)(H1,H9-H2tp)(H9-Ht...

A 13-membered ring cyclic tetrapeptide was synthesized by the solid-phase peptide synthesis method, and its copper(II) coordination properties were analyzed by optical spectroscopy, mass spectrometry, and electrochemistry. All collected data strongly support the presence, at alkaline pH, of a stable peptide/copper(III) complex that is formed in solution by atmospheric dioxygen oxidation. On the basis of previous studies on cyclic peptide/copper systems, we suggest that the copper(III) ion is at the center of the ligand's cavity being coordinated to four deprotonated amide nitrogen atoms. This donor set would greatly lower the redox potential for the CuIII/CuII couple, thus allowing easy oxidation of the coordinated copper(II) by atmospheric oxygen.

The first dendrimers containing metallacarborane modules have been prepared and characterized. The acyl derivative nido-[η5-C5H4C(O)Cl]Co(2,3-Et2C2B3H5) was treated with diaminobutane-dend(NH2)16 (...

By reaction of the geometrically incomplete cubane-like clusters [(eta(5)-Cp')(3)Mo(3)S(4))][pts] and [(eta(5)-Cp')(3)W(3)S(4)][pts] (Cp' = methylcyclopentadienyl; pts = p-toluenesulfonate) with group 10 alkene complexes, three new heterobimetallic clusters with cubane-like cluster cores were isolated: [(eta(5)-Cp')(3)W(3)S(4)M'(PPh(3))][pts] ([5][pts], M' = Pd; [6][pts], M' = Pt); [(eta(5)-Cp')(3)Mo(3)S(4)Ni(AsPh(3))][pts] ([7][pts]). The compounds [5][pts]-[7][pts] are completing the extensive series of clusters [(eta(5)-Cp')(3)M(3)S(4)M'(EPh(3))][pts] (M = Mo, W; M' = Ni, Pd, Pt; E = P, As) which allows the consequences of replacing a single type of atom on structural and NMR and UV/vis spectroscopic as well as electrochemical properties to be determined. Single-crystal X-ray structure determinations of [5][pts]-[7][pts] revealed that [5][pts] was not isomorphous to the other members of the series [(eta(5)-Cp')(3)M(3)S(4)M'(EPh(3))][pts] due to distinctly different cell parameters, which in the molecular structure of [5](+) is reflected in a slightly different orientation of the PPh(3) ligand. Electrochemical measurements on the series showed that the Mo-based clusters were more difficult to oxidize than their W-based analogues. The Pd-containing clusters underwent two-electron oxidation processes, whereas the Ni- and Pt-containing clusters underwent two separated one-electron oxidation processes.