New ruthenium(II) precursors with the tetradentate sulfur macrocycles tetrathiacyclododecane ([12]aneS4) and tetrathiacyclohexadecane ([16]aneS4) for the construction of metal-mediated supramolecular assemblies

Di- and Tri-nuclear VIII and CrIII Complexes of Dipyridyltriazoles: Ligand Rearrangements, Mixed Valency and Ferromagnetic Coupling

The first dinuclear and trinuclear chromium(III) and dinuclear vanadium(III) complexes of N⁴-R-substituted-3,5-di(2-pyridyl)-1,2,4-triazole (Rdpt) ligands have been prepared by solvothermal complexations under inert atmospheres, and characterized. The reactions of Cr^III and V^III with adpt (R = amino) resulted in deamination of the ligand and yielded the dinuclear doubly-triazolate bridged complexes [V2III(dpt⁻)₂Cl₄] (1) and [Cr2III(dpt⁻)₂Cl₄] (2). In the case of the Cr^III complex 2 this bridging results in a rare example of ferromagnetic coupling for a dinuclear Cr^III compound. DFT studies confirm that in 2 the ferromagnetic coupling pathways dominate over the antiferromagnetic pathways, whereas in 1 the reverse occurs, consistent with the observed overall antiferromagnetic coupling in that case. It was also found that the use of different additives in the reaction allows the nuclearity of the Cr^III product to be manipulated, giving either the dinuclear system, or the first example of a trinuclear circular helicate for a Rdpt complex, [Cr3III(dpt)₃Cl₆]·1¾MeCN·¼DCM (3). Reaction of N⁴-pydpt (R = 4-pyridyl) with V^III led to an unusual shift of the pyridyl substituent from N⁴ to N¹ of the triazole, forming the ligand isomer N¹-pydpt, and giving a dinuclear doubly-triazole bridged complex, [V2III(N¹-pydpt)₂Cl₆]·2MeCN (4). Reaction with Cr^III results in loss of the 4-pyridyl ring and a mixture of the di- and trinuclear complexes, 2 and 3. Interestingly, partial oxidation of the V^III in dinuclear complex 4 to vanadyl V^IV=O was identified by crystallographic analysis of partially oxidized single crystals, [(V^IVO)_0.84(V^III)_1.16(N¹-pydpt)₂Cl_5.16]·0.84H₂O·1.16MeCN (5).

Modulating the electron-transfer properties of a mixed-valence system through host-guest chemistry

Herein, we report that the interplay between the binding properties and redox activity of a self-assembled trinuclear Ru^II macrocycle leads to an hitherto unreported phenomenon, in which access to specific MV states is gated by host–guest chemistry.

Metal directed self-assembly has become a much-studied route towards complex molecular architectures. Although studies on mixed valence, MV, systems accessible through this approach are almost non-existent, the potential applications of such systems are very exciting as MV states provide the basis of a number of molecular-scale devices, including single electron wires and switches. Furthermore, while many novel hosts for guest ions and molecules have been developed through metal directed self-assembly, as these products tend to be kinetically labile, very few electrochemical studies have been reported. Herein, we report that the interplay between the binding properties and redox activity of a self-assembled trinuclear Ru^II macrocycle leads to an hitherto unreported phenomenon, in which access to specific MV states can be gated by host–guest chemistry. Thus, this system is the first in which MV states and the extent of electron delocalisation are switched by an ion without any change in electrochemical potential.

Synthetic strategies towards ruthenium-porphyrin conjugates for anticancer activity

The conjugation of porphyrins to metal fragments is a strategy for making new compounds that are expected to combine the phototoxicity and the tumour-localization properties of the porphyrin chromophore with the cytotoxicity of the metal fragment for additive antitumour effect. We report here the preparation of new classes of porphyrin-ruthenium conjugates with potential bio-medical applications. Ruthenium was chosen because several Ru compounds have shown promising anticancer activity. The conjugation with the porphyrin moiety was accomplished either through peripheral pyridyl rings (e.g.meso-4'-tetrapyridylporphyrin, 4'TPyP) or through bpy units (e.g.meso-(p-bpy-phenyl)porphyrins, bpy(n)-PPs, n = 1-4). The number of Ru fragments attached to the porphyrins ranges from 1 to 4 and the total charge of the conjugates from -4 to +8. Different types of peripheral fragments, both Ru(III) and Ru(II), have been used: in some cases they are structurally similar to established anticancer compounds. Examples are [Na](4)[4'TPyP{trans-RuCl(4)(dmso-S)}(4)] (2), that bears four NAMI-type Ru(III) fragments, or [4'TPyP{Ru([9]aneS3)(en)}(4)][CF(3)SO(3)](8) (3) and [bpy(4)-PP{Ru([9]aneS3)(dmso-S)}(4)][CF(3)SO(3)](8) (9) (en = ethane-1,2-diamine, [9]aneS3 = 1,4,7-trithiacyclononane) that have four half-sandwich Ru(II) compounds. The Ru fragments may either contain one or more labile ligands, such as in 2 or in 9, or be coordinatively saturated and substitutionally inert, such as in 3 or in [bpy(4)-PP{Ru([12]aneS4)}(4)][CF(3)SO(3)](8) (11) ([12]aneS4 = 1,4,7,10-tetrathiacyclododecane). Most of the ruthenium-porphyrin conjugates described in this work are soluble--at least moderately--in aqueous solution and are thus suitable for biological investigations, in particular for cytotoxicity and photo-cytotoxicity tests.