Dinuclear Bis Research Articles

Characterization of a Dinuclear (&mgr;-Hydroxo)(&mgr;-pyrazolato)dimanganese(II) Complex and Hydrolytic Equilibrium of the Bridging Pyrazolate Ligand.

Reaction of the dinuclear bis(μ-hydroxo) complex 2 with 3,5-diisopropylpyrazole yielded a dinuclear (μ-hydroxo)(μ-pyrazolato)dimanganese(II) complex 4, which reacted with H2O2 in the absence of excess pyrazole to give the mononuclear Mn(III) side-on peroxo complex containing a neutral pyrazole ligand. However, hydrolytic equilibrium of the bridging pyrazolate ligand of the (μ-hydroxo)(μ-pyrazolato)dimanganese(II) complex was observed in the presence of H2O.

Dicompartmental Ligands with Hexa- and Tetradentate Coordination Sites: One-Step Synthesis of Ligands and Metal Complexes and Their X-ray Structure Analysis

Examples of interesting ligands previously requiring lengthy synthetic procedures have been prepared by one-step routes, opening the way to more extensive studies of their complexes and to possible applications. New dicompartmental ligands bearing picolyl pendant arms on the amine nitrogen donors have been synthesized, via the Mannich condensation, from 5-substituted salicylaldehydes, formaldehyde, and N,N‘-bis(2-pyridylmethyl)-1,2-diaminoethane. The protonated acyclic ligand salt, two mononuclear complexes of a macrocyclic ligand with a second compartment featuring a Schiff base, and one of the decomposition products resulting from a retro-Mannich reaction have been structurally characterized. The ligand salt (L1b) has an extended conformation with the ethylenediamine fragment displaying the trans configuration, very different from that of the corresponding closed-site macrocyclic complexes NiH2(L2b)2+ and ZnH2(L2b)2+. The mononuclear macrocyclic complex NiH2(L2b)2+ has a much smaller ligand twist than the corresponcing Zn(II) complex. The degree of ligand distortion is correlated with the M−N bond length between the metal ions and the pyridine nitrogens; longer M−N bonds cause the pyridine rings to tilt and twist the phenolic rings out of the main ligand plane. The ability of the macrocyclic ligand L2b to accommodate a second metal ion has been demonstrated by successful synthesis of dinuclear complexes. The free carbonyl groups of the open-site ligand were transformed into oxime groups, and the corresponding dinuclear bis(nickel) complex has been prepared. Acetal formation by the free carbonyl groups of ligand and retro-Mannich rearrangements are found to be possible pathways for the decomposition of this family of dicompartmental ligands.

Structure and NMR Behavior of Cobalt(III) Polyamine Complexes of α,ω-Alkylenediamine-N,N,N′,N′-tetramethylenetetraphosphonate in Aqueous Solution

Abstract The complex formation of α,ω-diaminopolyphosphonates (ethylenediamine- [H8edtmp], trimethylenediamine- [H8tdtmp] and hexamethylenediamine-N,N,N′,N′-tetramethylenetetraphosphonate [H8hdtmp]) with cobalt(III) polyamine complexes has been investigated by means of 31P NMR spectroscopy. The formation and protonation constants of the complexes and the 31P NMR chemical shifts of each protonated species were determined from the pH dependence of the 31P NMR signals. In any complexes, the nitrogen atom of the ligand is not coordinated to CoIII. The complex cis-[CoCl(en)2(NH3)]2+ forms a mononuclear O-monodentate complex and two types of binuclear bis(O-monodentate) complexes by a reaction with edtmp and tdtmp, and forms a mononuclear O-monodentate complex and a dinuclear bis(O-monodentate) complex with hdtmp. The complex cis-[CoCl2(en)2]+ forms a mononuclear O-monodentate complex and a mononuclear O,O-bidentate complex having an eight-membered chelate ring with edtmp and tdtmp, and forms a mononuclear O,O-bidentate complex and dinuclear bis(O-monodentate) complexes with hdtmp. In the case of the edtmp complexes, two iminodiphosphonate groups interact with each other: 1) an interaction between the nitrogen atoms of two imino fragments by a hydrogen bond (NH+···N) in a monoprotonated species and 2) an intramolecular interaction between the protonated nitrogen atom and phosphonate O− of another imino group (NH+···−OP) in triprotonated and tetraprotonated species.

A circular dichroism study of ethidium bromide binding to Z-DNA induced by dinuclear platinum complexes

Dinuclear bis(platinum) complexes have been shown previously to induce the B → Z transition in synthetic DNAs ( Nucleic Acids Res. 7, 1697–1703; J. Inorganic Biochem. 54, 207–220). In this paper, the reversibility of the Z conformation back to the B form was assessed by treatment of the induced Z form in poly(dG-dC).poly(dG-dC) with ethidium bromide (Etd). Z-DNA induced by the tetra-amine cations [{Pt(NH 3) 3} 2(H 2N(CH 2) nNH 2)] 4+, which are capable of only electrostatic interactions with the polynucleotide, was readily reversible. The spectroscopic data mirrored that of ethidium bromide/poly(dG-dC).poly(dG-dC) in the presence of 4.4 M NaCl. In contrast, Z-DNA induced by the bifunctional complexes [{ trans-PtCl(NH 3) 2} 2(H 2N(CH 2) nNH 2)] 2+ did not produce spectra typical of Etd intercalation and reversal to B-form DNA. The original Z-form CD spectra of DNA treated with the bifunctional complexes could be reobtained following removal of Etd by extensive dialysis. The bifunctional complexes are very effective interstrand cross-linking agents. The data suggest that interstrand cross-linking by dinuclear complexes can stabilize or “lock” the Z-conformation prohibiting its reversal to the B-form. The implications for the biological activity of the dinuclear complexes are briefly discussed.

Dynamic Behavior, Redistribution Reactions, and Intermetallic Distances of Dinuclear Bis(μ-pyrazolato)rhodium(I) Complexes

Dynamic Behavior, Redistribution Reactions, and Intermetallic Distances of Dinuclear Bis(μ-pyrazolato)rhodium(I) Complexes

Bridged bis(imido)molybdenum complexes: isolobal analogues of ansa-zirconocenes and bizirconocenes

The first complexes containing chelating bis(imide) ligands and a novel dinuclear bis(imido) derivative have been synthesized and characterised by X-ray crystallography.

Synthesis of functionalized platinum complexes containing dimethylsulfoxide as leaving group. Observation of novel steric control of intrastrand versus interstrand cross-linking by use of bulky ligands

Dinuclear bis(platinum) cations, containing as potential leaving group dimethylsulfoxide (Me 2SO), were prepared. The general formula is [{ trans-Pt(Me 2SO)(NH 3) 2} 2NH 2(CH 2) nNH 2] 4+. These complexes were found to induce the Z form of poly(dG-dC).poly(dG-dC). The complexes also appear to bind to DNA forming interstrand cross-links by displacement of Me 2SO. In aqueous solution, rapid hydrolysis occurs to free diamine and the trans-[Pt(H 2O)(Me 2SO)(NH 3) 2] 2+ cation. In a surprising finding, this monomeric species (as the chloride trans-[PtCl(Me 2SO)(NH 3) 2] +) was found to be a much more efficient interstrand cross-linking agent than the parent trans-[PtCl 2(NH 3) 2]. Thus, steric control by bulky ligands such as Me 2SO may be used to affect relative tendencies to inter- or intrastrand cross-link formation in platinum complexes.

Reaction of primary silanes with dinuclear rhodium hydride complexes: silane coupling reactions

The reaction of the dinuclear rhodium hydride dimer [(dippe)Rh] 2(μ-H) 2 (dippe=l,2-bis(diisopropylphosphino)ethane) with primary silanes is described. In the presence of two equivalents of RSiH 3 (R=Bu n and Tol P), dinuclear bis(μ-silylene) complexes of the formula [(dippe)Rh] 2(μ-SiHR) 2 result. Attempts to generate silylhydride complexes of the formula [(dippe)Rh] 2(μ-H)(μ-H-SiHR) by the addition of one equiv. of RSiH 3 failed. The bis(μ-silylene) complexes react with hydrogen to form adducts wherein two equivalents of H 2 per dimer unit have been activated; on the basis of NMR spectral studies these complexes are proposed to have the following formula: [(dippe)RhH] 2(μ-H-SiHR) 2. These molecules are extremely fluxional and lose H 2 rather readily. Addition of more than three equivalents of primary silane to 1 generated dinuclear rhodium derivatives with three silicon-containing ligands, having the formula [(dippe)Rh] 2(μ-SiHR)(μ-H-SiHR) 2. In the presence of excess primary silane, the dinuclear rhodium hydride 1 acts as a catalyst precursor for the dehydrogenative coupling of silanes. With the p-tolylsilane, dimerization does occur but the process is complicated by dispro- portionation reactions to generate (Tol P) 2SiH 2 and (Tol P) 3SiH; with butylsilane, SiSi chains with up to five silicons have been produced with no evidence of disproportionation. Crystals of [(dippe)Rh] 2(μ-SiHBu n) 2 ( 2a) are monoclinic, a=10.889(1), b=13.105(2), c=16.676(2) Å,β=104.06(1)°, Z=2, space group P2 1/n.; and those of [(dippe)Rh] 2(μ-η 2-H-SiHTol P) 2(μ-SiHTol P) ( 4b) are monoctinic, a=25.839(4), b=13.084(3), c=17.133(3) Å, β=107.10(1)°, Z=4, space group P21/ a. The structures were solved by Patterson ( 2a) and direct ( 4b) methods and were refined by full-matrix least-squares procedures to R=0.035 and 0.047 ( R w=0.030 and 0.060) for 3184 and 5997 reflections with 1⩾3η( I), respectively.

Nonclassical platinum antitumor agents: perspectives for design and development of new drugs complementary to cisplatin.

Studies over the last few years have shown that the range of platinum complexes with useful cytotoxicity and antitumor activity is not strictly limited to structural analogs of cisplatin. In general, we can expect that cells will process structurally different species in different manners. The metabolic chemistry and DNA binding will be altered in in comparison to the cis-[PtX2 (amine)2] class. This point is of particular importance because any altered pattern of antitumor activity of structural analogs of cisplatin is likely to be due to unpredictable pharmacokinetic, rather than truly mechanistic, factors. The fact that discrete cisplatin-DNA adducts vary in their biological activity further supports the hypothesis that complexes structurally dissimilar to cisplatin may produce biological activity complementary to the parent drugs. The mechanism of action of nonclassical complexes is different from that of cisplatin and its analogs. Their pattern of antitumor activity is also altered with respect to cisplatin--thus, not all platinum-containing drugs need necessarily be similar in their clinical profile to cisplatin. Note that both the dinuclear bis(platinum) complexes and the trans complexes give their own distinct patterns of tumor specificity--different from cisplatin and each other (see Tables 1 and 3). New cytotoxic mechanisms for platinum complexes may also be placed in context with cisplatin resistance. Modes of overcoming cisplatin resistance may reside at the various levels of uptake, interaction with "detoxifying" intracellular thiols, and DNA repair. Likewise complexes with novel mechanisms of action may circumvent resistance by more than one unique route. Indeed, the three major routes to resistance are all affected to varying degrees by the complexes outlined above. From the discovery of cisplatin, the development of analogs has essentially been an empirical exercise. Because of their similar mechanism of action, much comparison has been made between platinum complexes and the classic alkylating agents. Yet the alkylating agents represent a good example where a number of structurally distinct drugs with different anticancer activities are clinically available. This desirable feature may be achieved for platinum complexes by emphasis on complexes structurally dissimilar to the presently used agents. The dinuclear bis(platinum) complexes and mononuclear complexes in the trans geometry are of special interest. Comparison of common features and differences between different classes may point to guidelines for the rational design of complexes with a different spectrum of clinical antitumor activity to cisplatin and activity against cisplatin-resistant tumors.

Synthetic strategies for dinuclear platinum complexes containing inequivalent coordination spheres. Design of complexes capable of specific attack at one platinum center

Synthetic strategies to dinuclear bis(platinum) complexes with inequivalent Pt coordination spheres are outlined. The isomeric pair of complexes containing formally a [PtCl 2(Me 2SO)(amine)] coordination sphere linked to a [PtCl 2(amine) 2] moiety giving a bis(platinum) complex [{PtCl 2(NH 3)}-NH 2(CH 2) 4H 2N-{PtCl 2(Me 2SO)}] ( cis/cis complex I, trans/trans complex II) has been prepared. Displacement reactions using pyridine on the tetra-iodo derivative of I gives evidence of selective substitution on the [PtI 2(H 2NR)(Me 2SO)] coordination sphere. Isomerisation of [{ trans-PtCl 2(Me 2SO)} 2NH 2(CH 2) 4NH 2] to the dinuclear cis derivative can occur initially in a reaction which is competitive with bridge cleavage.

B↑ Z DNA conformational changes induced by a family of dinuclear bis(platinum) complexes

The reactions of bis(platinum) complexes of general formula [(PtClm(NH3)3-m)2(NH2(CH2)nNH2)]2(2-m)+ were studied with poly(dG-dC).poly(dG-dC), poly(dG-m5dC).poly(dG-m5dC) and poly(dG).poly(dC). When m = 0 (Complexes II, n = 2,4) the complexes are saturated 4+ cations capable only of electrostatic interactions with the polynucleotide. Where m = 1 the complexes contain two monodentate platinum coordination spheres with the chloride trans to the diamine bridge (Complexes I, n = 2,4, 1,1/t,t). Complexes I give CD spectra characteristic of a 'Z-like' conformation upon reaction with poly(dG-dC).poly(dG-dC) and poly(dG-m5dC).poly(dG-m5dC) but not poly(dG).poly(dC). The B----Z transition appears independent of interplatinum diamine chain length. As little as 1 bis(platinum) complex per 25-30 base pairs is sufficient to observe the Z-like spectrum. Covalent binding is however not a prerequisite for Z-DNA formation because the polyvalent cations II are also very effective in inducing the B----Z transition in either poly(dG-dC).poly(dG-dC) or poly (dG-m5dC).poly(dG-m5dC). In these cases, the concentrations of II required are significantly lower than analogous monomeric agents such as [Co(NH3)6]3+. The possible biological consequences of the Z-DNA induction by bis(platinum) complexes are discussed.

Organische Synthesen mit Übergangsmetallkomplexen, 42 Allene als Liganden in zweikernigen Eisencarbonyl‐Komplexen; Carbonylierungen von Allenen sowie deren Kupplung mit Alkinen und Allenen; dynamische “Keten‐Scheibenwischer”‐Komplexe

Organic Syntheses via Transition Metal Complexes, 42. - Allenes in Dinuclear Iron Carbonyl Complexes; their Carbonylation and Coupling with Alkynes and Allenes; Fluxional “Ketene Windshield-Wiper” Complexes On photochemically induced metallation with pentacarbonyl iron allenes H2C = C = CHR 1 (R = H, C6H5) give dinuclear acyl iron complexes 2, in which the central carbon of the C = C = C unit is attached to a carbonyl group. 2 on warming yield π-ally1,σ complexes 3 by loss of carbon monoxide. The reaction 2 ⇌ 3 + CO is reversibel. 3 add alkynes R1 - C = C - R24 (R1 = C6H5r, CH2OCH3; R2 = Hr C6H5) with insertion of the C = C triple bond into the M - C σ-bond to give dinuclear ketene complexes 5. The latter are fluxional, as was shown by NMR measurements. The ketene unit is moving back and forth like a windshield wiper. Thermolysis of 5 under normal pressure affords ferracyclopentadiene iron complexes 6 (by 1,3-hydrogen shifts) and 4-methylene-2-cyclopenten-1-one 7 (by cyclocarbonylation). Thermolysis of 5 under CO pressure gives 7 as the sole products. Complexes 3 also add allenes 1 with insertion into the M–C σ-bond and formation of a C–C bond between the central carbon atoms of both allene units to give dinuclear bis(allyl) complexes 8 and 8′.

Reaktionen von Propiolaldehydacetalen mit Dicarbonylcyclopentadienylmangan-Fragmenten

Reactions of a dicarbonylcyclopentadienylethermanganese complex ( 1) with propiolic aldehyde acetals ( 2) yield the mononuclear dicarbonylcyclopentadienyl-η 2-(propiolic aldehyde acetal)manganese compounds CpMn(CO) 2HCCCH(OR) 2 (R  Me, 3a; R  Et, 3b; (OR) 2O(CH 2) 3O, 3c). In addition dinuclear bis(dicarbonylcyclopentadienyl)dialkoxymethylvinylidene complexes [CpMn(CO) 2] 2CC(H)CH(OR) 2 (R  Me, 5a; R  Et, 5b and (OR) 2O(CH 2) 3O, 5c) and a bis(dicarbonylcyclopentadienylmanganese)-2-carbaldehydevinylidene species ( 5d) have been isolated. These dinuclear compounds were also obtained via dicarbonylcyclopentadienyl(dialkoxymethylvinylidene)manganese derivatives CpMn(CO) 2CC(H)CH-(OR) 2 (R  Me, 4a; R  Et, 4b; (OR) 2O(CH 2) 3O, 4c), which were synthesized by an independent route. 3c, 5c and 5d were characterized by X-ray analyses diffraction studies.

ChemInform Abstract: Synthesis and Characterization of Mononuclear and Dinuclear Bis(2,2′‐bipyridine)ruthenium(II) Complexes Containing Sulfur‐Donor Ligands.

AbstractStarting with (I), a series of the title complexes involving those containing coordinated (WS4)2‐, polysulfide S52‐, aliphatic and aromatic thiolate, and dithiolene ligands is prepared.

Synthesis and characterization of mononuclear and dinuclear bis(2,2'-bipyridine)ruthenium(II) complexes containing sulfur-donor ligands

Preparation d'une serie de complexes du ruthenium(II). Etude radiocristallographique, spectrometrie UV visible, RPE et voltammetrie cyclique

Metallaheterocumulene: III. Ungewöhnliche bildung von (CO) 5CrCNCPh 2NCCr(CO) 5 bei der reaktion von [(CO) 5CrCNCPh 2] + AlBr 4− mit tetrahydrofuran

Pentacarbonyl(3,3-diphenyl-2-azaallenylidene)chromium tetrabromoaluminate, [(CO) 5CrCNz.dbnd;CPh 2] + AlBr 4 −, reacts with THF in dichloromethane to give the dinuclear bis(isonitrile) complex [(CO) 5CrCN] 2CPh 2 which formally corresponds to the product of a reductive dimerization of two [(CO) 5CrCNCPh 2] + moieties with concomitant elimination of one CPh 2 fragment.

Übergangsmetall-methylen-komplexe: IXL. Über metallzentrierte umlagerungsreaktionen von diazoalkanen und die einfache synthese von alkylidenamido- sowie isocyanato-komplexen

The dinuclear 2-diazopropane complex 1 undergoes a novel type of fragmentation upon heating in boiling toluene: irreversible nitrogennitrogen bond cleavage of the metal-coordinated heterocumulene with subsequent rearrangement of the intermediate nitrido(carbonyl)metal species yields a terminal isocyanato ligand while the remaining 2-propylidene amido fragment symmetrically bridges the metalmetal double bond ( d(MoMo) 274.5(2) pm) of the reaction product 2. This unexpected rearrangement reaction is to be considered as a further variant of the “Hieber base reaction”. A chemical test of the multiple bond character of the molybdenummolybdenum bond present in compound 2 was provided by the reversible addition of carbon monoxide which reaction yields compound 3. Insertion of a nitrido metal moiety into a methylene bridge was observed, for the first time, in the case of the methodologically related rearrangement process of the diazomethane derivative 4; the resulting dinuclear bis(methylene amido) derivative 5 was again characterized by means of X-ray diffraction techniques.