Designing organometallic compounds for catalysis and therapy

Bioorganometallic chemistry is a rapidly developing area of research. In recent years organometallic compounds have provided a rich platform for the design of effective catalysts, e.g. for olefin metathesis and transfer hydrogenation. Electronic and steric effects are used to control both the thermodynamics and kinetics of ligand substitution and redox reactions of metal ions, especially Ru II. Can similar features be incorporated into the design of targeted organometallic drugs? Such complexes offer potential for novel mechanisms of drug action through incorporation of outer-sphere recognition of targets and controlled activation features based on ligand substitution as well as metal- and ligand-based redox processes. We focus here on η 6-arene, η 5-cyclopentadienyl sandwich and half-sandwich complexes of Fe II, Ru II, Os II and Ir III with promising activity towards cancer, malaria, and other conditions. © 2012 The Royal Society of Chemistry

Hypoxia Sensitive Metal β-Ketoiminate Complexes Showing Induced Single Strand DNA Breaks and Cancer Cell Death by Apoptosis

A series of ruthenium and iridium complexes have been synthesised and characterised with 20 novel crystal structures discussed. The library of β-ketoiminate complexes has been shown to be active against MCF-7 (human breast carcino-ma), HT-29 (human colon carcinoma), A2780 (human ovarian carcinoma) and A2780cis (cisplatin resistant human ovarian carcinoma) cell lines, with selected complexes being more than three times as active as cisplatin against the A2780cis cell line. Complexes have also been shown to be highly active under hypoxic conditions, with the activities of some complexes increasing with a decrease in O2 concentration. The enzyme thioredoxin reductase is over-expressed in cancer cells and complexes reported herein have the advantage of inhibiting this enzyme, with IC50 values measured in the nanomolar range. The anti-cancer activity of these complexes was further investigated to determine whether activity is due to effects on cellular growth or cell survival. The complexes were found to induce significant cancer cell death by apoptosis with levels induced correlating closely with activity in chemosensitivity studies. As a possible cause of cell death, the ability of the complexes to induce damage to cellular DNA was also assessed. The complexes failed to induce double strand DNA break or DNA crosslinking but induced significant levels of single DNA strand breaks indi-cating a different mechanism of action to cisplatin

Hydrolytic behaviour of mono-and dithiolato-bridged dinuclear arene ruthenium complexes and their interactions with biological ligands

The hydrolysis and the reactivity of two dinuclear p-cymene ruthenium monothiolato complexes, [(η6-p-MeC6H4Pri)2Ru2Cl2(µ-Cl)(µ-S-m-9-B10C2H11)] (1) and [(η6-p-MeC6H4Pri)2¬Ru2Cl2(µ-Cl)¬(µ-S¬CH2-p-C6H4-NO2)] (2), and of two dinuclear p-cymene ruthenium dithiolato complexes, [(η6-p-MeC6H4Pri)2Ru2(µ-SCH2CH2Ph)2Cl2] (3) and [(η6-p-Me¬C6H4¬Pri)2¬Ru2(S¬CH2¬C6H4-p-O¬Me)2¬Cl2] (4) towards amino acids, nucleotides, and a single-stranded DNA dodecamer were studied using NMR and mass spectrometry. In aqueous solutions at 37 °C, the monothiolato com¬plexes 1 and 2 undergo rapid hydrolysis, irrespective of the pH value, the predominant species in D2O/acetone-d6 solution at equilibrium being the neutral hydroxo complexes [(η6-p-Me¬C6H4¬Pri)2Ru2(OD)2(µ-OD)(µ-SR)]. The dithiolato complexes 3 and 4 are stable in water under acidic conditions, but undergo slow hydrolysis under neutral and basic conditions. In both cases, the cationic hydroxo complexes [(η6-p-MeC6H4Pri)2Ru2(µ-SR)2¬(OD)¬(CD3CN)]+ are the only spe¬cies observed in D2O/CD3CN at equilibrium. Surprisingly, no adducts are observed upon addition of an excess of L-methionine or L-histidine to the aqueous solutions of the complexes. Upon addition of an excess of L-cysteine, on the other hand, 1 and 2 form the unusual cationic trithiolato complexes [(η6-p-MeC6H4Pri)2¬Ru2{µ-SCH2CH(NH2)COOH}2(µ-SR)]+ containing two bridging cysteinato li¬gands, while 3 and 4 yield cationic trithiolato complexes [(η6-p-MeC6H4Pri)2Ru2[µ-SCH2CH¬(NH2)COOH](µ-SR)2]+ containing one bridging cysteinato ligand. A representative of catio¬nic trithiolato complexes containing a cysteinato bridge of this type, [(η6-p-MeC6H4Pri)2¬Ru2[µ-S¬CH2CH(NH2)COOH](µ-SCH2-p-C6H4-But)2]+ (6) could be synthesised from the di¬thiolato complex [(η6-p-Me¬C6H4¬Pri)2-Ru2(S¬CH2¬C6H4-p-But)2Cl2] (5), isolated as the tetra¬fluo¬ro¬borate salt and fully characterised. Moreover, the mono- and dithiolato complexes 1 - 4 are inert toward nucleotides and DNA, suggesting that DNA is not a target of cytotoxic thiolato-bridged arene ruthenium complexes. In contrast to the trithiolato complexes, monothiolato and dithio¬lato complexes hydrolyse and react with L-cysteine. These results may have im¬portant implications for the mode of action of thiolato-bridged dinuclear arene ruthenium drug candidates, and suggest that their modes of action are different to those of other arene ruthenium complexes

Electrochemical and photochemical conversion of [Ru3Ir(mu(3)-H)(CO)(13)] into [Ru3Ir(mu-H)(3)(CO)(12)]

Electrochemical and photochemical properties of the tetrahedral cluster [Ru3Ir(mu(3)-H)(CO)(13)] were studied in order to prove whether the previously established thermal conversion of this cluster into the hydrogenated derivative [Ru3Ir(mu-H)(3)(CO)(12)] also occurs by means of redox or photochemical activation. Two-electron reduction of [Ru3Ir(mu(3)-H)(CO)(13)] results in the loss of CO and concomitant formation of the dianion [Ru3Ir(mu(3)-H)(CO)(12)](2-). The latter reduction product is stable in CH2Cl2 at low temperatures but becomes partly protonated above 283 K into the anion [Ru3Ir(mu-H)(2)(CO)(12)](-) by traces of water. The dianion [Ru3Ir(mu(3)-H)(CO)(12)](2-) is also the product of the electrochemical reduction of [Ru3Ir(mu-H)(3)(CO)(12)] accompanied by the loss of H-2. Stepwise deprotonation of [Ru3Ir(mu-H)(3)(CO)(12)] with Et4NOH yields [Ru3Ir(mu-H)(2)(CO)(12)](-) and [Ru3Ir(mu(3)-H)(CO)(12)](2-). Reverse protonation of the anionic clusters can be achieved, e. g., with trifluoromethylsulfonic acid. Thus, the electrochemical conversion of [Ru3Ir(mu(3)-H)(CO)(13)] into [Ru3Ir(mu-H)(3)(CO)(12)] is feasible, demanding separate two-electron reduction and protonation steps. Irradiation into the visible absorption band of [Ru3Ir(mu3-H)(CO)(13)] in hexane does not induce any significant photochemical conversion. Irradiation of this cluster in the presence of CO with lambda(irr) > 340 nm, however, triggers its efficient photofragmentation into reactive unsaturated ruthenium and iridium carbonyl fragments. These fragments are either stabilised by dissolved CO or undergo reclusterification to give homonuclear clusters. Most importantly, in H-2-saturated hexane, [Ru3Ir(mu(3)-H)(CO)(13)] converts selectively into the [Ru3Ir(mu-H)(3)(CO)(12)] photoproduct. This conversion is particularly efficient at lambda(irr) > 340 nm

Isolation and single-crystal X-ray structure analysis of the catalyst–substrate host–guest complexes [C6H6⊂H3Ru3{C6H5(CH2)nOH}(C6Me6)2(O)]+ (n=2, 3)

The trinuclear arene-ruthenium cluster cations [H3Ru3{C6H5(CH2)nOH}(C6Me6)2(O)]+ (3: n=2, 4: n=3) have been synthesised from the dinuclear precursor [H3Ru2(C6Me6)2]+ and the mononuclear complexes [{C6H5(CH2)nOH}Ru(H2O)3]2+ in aqueous solution, isolated and characterised as the hexafluorophosphate or tetrafluoroborate salts. Both 3 and 4 are derivatives of the parent cluster cation [H3Ru3(C6H6)(C6Me6)2(O)]+ (1) which was found to catalyse the hydrogenation of benzene to give cyclohexane under biphasic conditions. The mechanism postulated for this catalytic reaction (‘supramolecular cluster catalysis’), involving the hydrophobic pocket spanned by the three arene ligands in 1, was based on the assumption that the substrate molecule benzene is hosted inside the hydrophobic pocket of the cluster molecule to form a catalyst–substrate host–guest complex in which the hydrogenation of the substrate takes place. With the analogous cluster cations 3 and 4, containing a (CH2)nOH side-arm (n=2, 3) as substituent at the benzene ligand, it was possible to isolate the cationic host–guest complexes as the hexafluorophosphate or tetrafluoroborate salts. The single-crystal X-ray structure analyses of [C6H6⊂3][PF6] and [C6H6⊂4][BF4], compared to that of [3][PF6] show that the substrate molecule benzene is indeed held inside the hydrophobic pocket of 3 and 4, the angle between the metal (Ru3) plane and the aromatic plane being 67° and 89°, respectively

Erratum to “Isolation and single-crystal X-ray structure analysis of the catalyst-substrate host–guest complexes [C6H6⊂H3Ru3{C6H5(CH2)nOH}(C6Me6)2(O)]+ (n=2,3)” [J. Organomet. Chem. 684 (2003) 117–123]

Figure 3 appeared twice and Figure 4 was missing; the cor. Figure 4 is given. [on SciFinder(R)

Supramolecular triruthenium cluster-based benzene hydrogenation catalysis: Fact or fiction?

The question is addressed of whether the triruthenium cluster cation [Ru-3(mu(2)-H)(3)(eta(6)C(6)H(6))(eta(6)-C6Me6)(2)(mu(3)-O)](+), 1, is a supramolecular, outer-sphere benzene hydrogenation catalyst or is 1 a precatalyst to well-known Ru(0)(n) catalysis of benzene hydrogenation. This question of "is it homogeneous or heterogeneous catalysis?" is especially important in the present case since if 1 is a supramolecular, homogeneous catalyst as postulated in the literature that is, if 1 can in fact accomplish catalysis of reactions as difficult as benzene reduction with no inner-sphere, d-orbital-mediated ligand dissociation, oxidative addition, migratory insertion, or reductive elimination-then that finding holds promise of rewriting the rules of organometallic-based catalysis. The identity of the true catalyst derived from 1 is, therefore, addressed by a collaborative effort between research groups at the Universite de Neuchatel and Colorado State University. The methodology employed is that worked out previously for addressing the historically vexing question of "is it homogeneous or heterogeneous catalysis?" (Lin, Y.; Finke, R. G. Inorg. Chem. 1994, 33, 489 1). A combination of the following classes of experiments have been employed: (i) Ru metal product studies; (ii) kinetic studies; (iii) Hg(0) and quantitative poisoning experiments, (iv) NMR studies of H/D exchange rates; (v) other data, plus (vi) the principle that the correct mechanism will explain all of the data. The results provide a compelling case that 1 is not the true benzene hydrogenation catalyst as previously believed; instead, all our evidence is consistent with, and supportive of, trace Ru(0) derived from 1 under the reaction conditions as the true, active catalyst. Nine additional conclusions are also presented as part of the summary and take-home messages, as well as a citation of "Halpern's rules" for catalysis

[η6-2-(2-Methylbenzoyloxy)ethyl methacrylate]bis(η6-1,2,4,5-tetramethylbenzene)tri-μ-hydrido-μ3-oxo-triruthenium(II)(3Ru—Ru) tetrafluoroborate

The trinuclear arene-ruthenium cluster cation, [Ru3H3(O)(C10H14)2(C14H16O4)](+), has been synthesized and crystallized as the tetrafluoroborate (BF4-) salt. The cations form, along the b axis, infinite one-dimensional chains through pi-stacking interactions