Comparative study of diastereoisomer interconversion in chiral BINOL-ate and diamine platinum complexes of conformationally flexible NUPHOS diphosphines

A thorough and detailed study of diastereointerconversion in the chiral platinum complexes [(NUPHOS)Pt{(S)-BINOL}] (3a-e) has been undertaken and compared with the results of a similar study with [(BIPHEP)Pt{(S)-BINOL}]. Rate data revealed that this process obeys first-order relaxation kinetics, and rate constants for conversion of the minor to the major diastereoisomer have been obtained. Eyring analysis of the data gave DeltaH(double dagger) and DeltaS(double dagger) values of 22-25 kcal mol(-1) and -1 to -16 eu, respectively. In combination with computational analysis, these studies indicate that atropinversion most likely occurs via an on-metal pathway involving a planar seven-membered transition state. Substitution of (S)-BINOL for (S,S)-DPEN results in a marked reduction in the barrier to atropinversion; a DeltaH(double dagger) value of 17 kcal mol(-1) has been determined for the conversion of delta-[(Ph-4-NUPHOS)Pt{(S,S)-DPEN}]Cl-2 to lambda-[(Ph-4-NUPHOS)Pt{(S,S)-DPEN}]Cl-2, which could indicate that an alternative mechanism operates.

A modular approach to luminescent dinuclear ruthenium(II) and rhenium(I) complexes

A series of dinuclear (bipyridine)tricarbonylrhenium(I) and tris(bipyridine)ruthenium(II) complexes have been isolated and characterised, bridged by a flexible diamido ethylene glycol chain. A new stepwise synthetic pathway has been investigated to heterometallic complexes, with the rhenium(I) complexes exhibiting an unusual configuration and inequivalence of the metal centres potentially arising from a surprising hydrogen-bonding interaction between an Re–CO group and an amide proton in low-polarity solvents. This interaction appears to be broken by competing hydrogen-bonding species such as dihydrogen phosphate. This effect was not observed in the corresponding ruthenium(II) complexes, which showed very little interaction with anions. The photophysical characterisation shows that the inclusion of two ester/amide groups to the rhenium centre effectively quenches the fluorescence at room temperature. The ruthenium(II) complexes have considerably stronger fluorescence than the rhenium species, and are less affected by theinclusion of ester and amide groups to the 2,2'-bipyridine chelating group.

Benzothiazole bipyridine complexes of ruthenium(II) with cytotoxic activity

A series of benzothiazole-substituted trisbipyridine ruthenium(II) analogues {[Ru(bpy)(2)(4,5'-bbtb)](2+), [Ru(bpy)(2)(5,5'-bbtb)](2+) and [Ru(bpy)(2)(5-mbtb)](2+) [bpy is 2,2'-bipyridine, bbtb is bis(benzothiazol-2-yl)-2,2'-bipyridine, 5-mbtb is 5-(benzothiazol-2-yl),5'-methyl-2,2'-bipyridine]} have been prepared and compared with the complex [Ru(bpy)(2)(4,4'-bbtb)](2+) reported previously. From the UV-vis spectral studies, substitution at the 5-position of the bpy causes the ligand-centred transitions to occur at considerably lower energy than for those with the functionality at the 4-position, while at the same time causing the emission to be effectively quenched. However, substitution at the 4-position causes the metal-to-ligand charge transfer to occur at lower energies. Fluorescent intercalator displacement studies indicate that the doubly substituted complexes displace ethidium bromide from a range of oligonucleotides, with the greater preference shown for bulge and hairpin sequences by the Lambda enantiomer. Since the complexes only show small variation in the UV-vis spectra on the introduction of calf thymus DNA and a small increase in fluorescence they do not appear to be intercalators, but appear to associate within one of the grooves. All of the reported bisbenzothiazole complexes show reasonable cytotoxicity against a range of human cancer cell lines.

Carboxyl-Functionalized Task-Specific Ionic Liquids for Solubilizing Metal Oxides

Imidazolium, pyridinium, pyrrolidinium, piperidinium, morpholinium, and quaternary ammonium bis(trifluoromethyl-sulfonyl)imide salts were functionalized with a carboxyl group. These ionic liquids are useful for the selective dissolution of metal oxides and hydroxides. Although these hydrophobic ionic liquids are immiscible with water at room temperature, several of them form a single phase with water at elevated temperatures. Phase separation occurs upon cooling. This thermomorphic behavior has been investigated by H-1 NMR, and it was found that it can be attributed to the temperature-dependent hydration and hydrogen-bond formation of the ionic liquid components. The crystal structures of four ionic liquids and five metal complexes have been determined.

A new approach for the detection of ethylene using silica-supported palladium complexes

The coordination of olefins to square-planar Pd(II) and Pt(II) complexes containing 2,9-dimethylphenanthroline (L1) often involves a change of color associated with a change of geometry at the metal center. In order to obtain suitable colorimetric detectors for ethylene gas, a series of new Pd(II) and Pt(II) compounds with a range of 2,9-disubstituted phenanthroline ligands [2,9-di-n-butyl-1,10-phenanthroline (L-2), 2,9-di-s-butyl-1,10-phenanthroline (L3), 2,9-diphenyl-1,10-phenanthroline (L4), and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (bathocuproine, L5)] have been prepared and their reactivity toward ethylene investigated both in solution and after depositing the detector compounds on a variety of solid supports. The Pd(II) complex [PdCl2(L2)] supported on silica undergoes a clear color change upon exposure to ethylene, while remaining stable toward air and water, and forms the basis for new simple colorimetric detectors with potential applications in ethylene pipe-leak detection and the monitoring of fruit ripening. Encouragingly, the detector is able to discriminate between fruit at different stages of ripening. The response of the detector to other volatiles was also examined, and specific color changes were also observed upon exposure to aromatic acetylenes. The crystal structures of four new derivatives, including the ethylene-Pt(II) complex [PtCl2(C2H4)(L2)], are also described.

Chromium, iron, ruthenium and gold complexes of 3,3-(biphenyl-2,2 '-diyl)-1-diphenylphosphino-1-phenylallene: A versatile ligand

Successive treatment of 9-(phenylethynyl)fluoren-9-ol (1a), with HBr, butyllithium and chlorodiphenylphosphine furnishes 3,3-(biphenyl-2,2'-diyl)-1-diphenylphosphino-1-phenylallene (5). Moreover, reaction of 1a directly with chlorodiphenylphosphine yields the corresponding allenylphosphine oxide (6). The allenylphosphine (5), and Fe-2(CO)(9) initially form the phosphine-Fe(CO)(4) complex, 11, which is very thermally sensitive and readily loses a carbonyl ligand. In the resulting phosphine-Fe(CO)(3) system, 12, the additional site at iron is coordinated by the allene double bond adjacent to phosphorus; the Fe(CO) 3 tripod in 12 exhibits restricted rotation on the NMR time-scale even at room temperature. The corresponding chromium complex, (5)-Cr(CO)5 (9), has also been prepared. The gold complexes (5)AuCl (13), and [(5)-Au(THT)](+) X-, where (THT) is tetrahydrothiophene, and X = PF6 (14a), or ClO4 (14b), are analogous to the known triphenylphosphine-gold complexes. In contrast, in the (arene)(allenylphosphine) RuCl2 system the allene double bond adjacent to phosphorus displaces a chloride, and the resulting cationic species undergoes nucleophilic attack by water yielding ultimately a five-membered Ru-P-C=C-O ruthenacycle (17). Thus, the allenylphosphine (5), reacts initially as a conventional mono-phosphine but, when the metal centre has a readily displaceable ligand such as a carbonyl or halide, the allene double bond adjacent to the phosphorus can also function as a donor. X- ray crystal structures are reported for 5, 6, 11, 12, 13, 14a, 14b and 17.

Visible-light-sensitized near-infrared luminescence from rare-earth complexes of the 9-hydroxyphenalen-1-one ligand

The unique absorption properties of the 9-hydroxyphenalen-1-one (HPHN) ligand have been exploited to obtain visible-light-sensitizable rare-earth complexes in 1: 3 and 1: 4 metal-to-ligand ratios. In both stoichiometries (1:3,tris,Ln(PHN)3;1:4, tetrakis, A[ Ln( PHN)(4)], with Ln being a trivalent rare-earth ion and A being a monovalent cation), the complexes of Nd(III),Er( III), and Yb(III) show typical near-infrared luminescence upon excitation with visible light with wavelengths up to 475 nm. The X-ray crystal structures of the tris complexes show solvent coordination to the central rare-earth ion, whereas in the tetrakis complexes, the four PHN-ligands form a protective shield around the central ion, preventing small solvent molecules from coordinating to the rare-earth ion, at least in the solid state.

Mandelohydroxamic acid as ligand for copper(II) 15-metallacrown-5 lanthanide(III) and copper(II) 15-metallacrown-5 uranyl complexes

The formation of pentanuclear copper(ii) complexes with the mandelohydroxamic ligand was studied in solution by electrospray ionization mass spectrometry (ESI-MS), absorption spectrophotometry, circular dichroism and H-1 NMR spectroscopy. The presence of lanthanide(iii) or uranyl ions is essential for the self-assembly of the 15-metallacrown-5 compounds. The negative mode ESI-MS spectra of solutions containing copper(II), mandelohydroxamic acid and lanthanide(iii) ions (Ln = La, Ce, Nd, Eu, Gd, Dy, Er, Tm, Lu, Y) or uranyl in the ratio 5:5:1 showed only the peaks that could be unambiguously assigned to the following intact molecular ions: {Ln(NO3)(2)[15-MCuIIN(MHA)-5](2-)}(-) and {Ln(NO3)[15-MCCuIIN(MHA)-5](3-)}(-), where MHA represents doubly deprotonated mandelohydroxamic acid. The NMR spectra of the pentanuclear species revealed only one set of peaks indicating a fivefold symmetry of the complex. The pentanuclear complexes synthesized with the enantiomerically pure R- or S-forms of mandelohydroxamic acid ligand, showed circular dichroism spectra which were mirror images of each other. The pentanuclear complex made from the racemic form of the ligand showed no signals in the CD spectrum. The UV/ Vis titration experiments revealed that the order in which the metal salts are added to the solution of the mandelohydroxamic acid ligand is crucial for the formation of metallacrown complexes. The addition of copper(ii) to the solutions containing mandelohydroxamic acid and neodymium(iii) in a 5:1 ratio lead to the formation of a pentanuclear complex in solution. In contrary, titration of lanthanide(iii) salt to the solution containing copper(ii) and mandelohydroxamic acid did not show any evidence for the formation of pentanuclear species. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Relaxometric study of copper [15]metallacrown-5 gadolinium complexes derived from alpha-aminohydroxamic acids

Proton nuclear magnetic relaxation dispersion (NMRD) profiles were recorded between 0.24 mT and 1.4 T for lanthanum(III)- and gadolinium(III)-containing [15]metallacrown-5 complexes derived from alpha-aminohydroxamic acids and with copper(n) as the ring metal. The influence of the different R-groups on the proton relaxivity was investigated, and a linear relationship between the relaxivity and the molecular mass of the metallacrown complex was found. The selectivity of the metallacrown complexes was tested by transmetalation experiments with zinc(n) ions. The crystal structure of the copper [15]metallacrown-5 gadolinium complex with glycine hydroximate ligands is reported.

Lanthanide(III) nitrobenzenesulfonates as new nitration catalysts: The role of the metal and of the counterion in the catalytic efficiency

Lanthanide(III) complexes of p-nitrobenzenesulfonic acid, Ln(p-NBSA)(3), m-nitrobenzenesulfonic acid, Ln(m-NBSA)(3), and 2,4-nitrobenzenesulfonic acid, Ln(2,4-NBSA)(3), were prepared, characterized and examined as catalyst for the nitration of benzene, toluene, xylenes, naphthalene, bromobenzene and chlorobenzene. The initial screening of the catalysts showed that lanthanum(III) complexes were more effective than the corresponding ytterbium(III) complexes, and that catalysts containing the bulky 2,4-NBSA ligand were less effective than the catalyst containing p-NBSA (nosylate) or m-NBSA ligands. Examination of a series of Ln(p-NBSA)(3) and Ln(m-NBSA)(3) catalysts revealed that there is a clear correlation between the ionic radii of the lanthanide(III) ions and the yields of nitration, with the lighter lanthanides being more effective. The X-ray single crystal structure of Yb(m-NBSA)(3).6H(2)O shows that two m-NBSA ligands are directly bound to the metal centre while the third ligand is not located in the first coordination sphere, but it is hydrogen bonded to one of the water molecules which is coordinated to ytterbium(III). NMR studies suggest that this structure is preserved under the conditions used in the nitration reaction. The structure of Yb(m-NBSA)(3) is markedly different from the structure of the well-known ytterbium(III) triflate catalyst. The coordination of the nitrobenzenesulfonate counterion to the lanthanide(III) ion suggests that steric effects might play an important role in determining the efficiency of these novel nitration catalysts. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).

Cobalt(II) Complexes of Nitrile-Functionalized Ionic Liquids

A series of nitrile-functionalized ionic liquids were found to exhibit temperature-dependent miscibility (thermomorphism) with the lower alcohols. Their coordinating abilities toward cobalt(II) ions were investigated through the dissolution process of cobalt(II) bis(trifluoromethylsulfonyl)imide and were found to depend on the donor abilities of the nitrile group. The crystal structures of the cobalt(II) solvates [Co(C1C1CNPyr)2(Tf2N)4] and [Co(C1C2CNPyr)6][Tf2N]8, which were isolated from ionic-liquid solutions, gave an insight into the coordination chemistry of functionalized ionic liquids. Smooth layers of cobalt metal could be obtained by electrodeposition of the cobalt-containing ionic liquids.

Sequential C-H and C-Ru bond formation and cleavage during the thermally induced rearrangement of aryl ruthenium(II) complexes with [C6H3(CH2NMe2)(2)-2,6](-) as a bidentate eta(2)-C,N coordinated ligand. The crystal structures of the isomeric pairs [RuCl{eta(6)-C10H14}{eta(2)-C,N-C6H3(CH2NMe2)(2)-2,n}] (n = 4 or 6) and [Ru(eta(5)-C5H5){(eta(2)-C,N-C6H3(CH2NMe2)(2)-2,n} (PPH3)] (n = 4 or 6)

New air-stable ruthenium(II) complexes that contain the aryldiamine ligand [C6H3(CH2-NMe2)(2)-2,6](-) (NCN) are described. These complexes are [RuCl{eta(2)-C,N-C6H3(CH2NMe2)(2)-2,6}(eta(6)-C10H14)] (2; C10H14 = p-cymene = C6H4Me-Pr-i-4), [Ru{eta(2)-C,N-C6H3(CH2NMe2)(2)-2,6}(eta(5)-C5H5)(PPh3)] (5), and their isomeric forms [RuCl{eta(2)-C,N-C6H3(CH2NMe2)(2)-2,4}(eta(6)-C10H14)] (3) and [Ru{eta(2)-C,N-C6H3(CH2NMe2)(2)-2,4}(eta(5)-C5H5)(PPh3)] (6), respectively. Complex 2 has been prepared from the reaction of [Li(NCN)](2) with [RuCl2(eta(6)-C10H14)](2), whereas complex 5 has been prepared by the treatment of [RuCl{eta(3)-N,C,N-C6H3(CH2NMe2)(2)-2,6}(PPh3)] (4) with [Na(C5H5)](n). Both 2 and 5 are formally 18-electron ruthenium(II) complexes in which the monoanionic potentially tridentate coordinating ligand NCN is eta(2)-C,N-bonded, In solution (halocarbon solvent at room temperature or in aromatic solvents at elevated temperature), the intramolecular rearrangements of 2 and 5 afford complexes 3 and 6, respectively. This is a result of a shift of the metal-C-aryl bond from position-1 to position-3 on the aromatic ring of the NCN ligand. The mechanism of the isomerization is proposed to involve a sequence of intramolecular oxidative addition and reductive elimination reactions of both aromatic and aliphatic C-H bonds. This is based on results from deuterium labeling, spectroscopic studies, and some kinetic experiments. The mechanism is proposed to contain fully reversible steps in the case of 5, but a nonreversible step involving oxidative addition of a methyl NCH2-H bond in the case of 2. The solid-state structures of complexes 2, 3, 5, and 6 have been determined by single-crystal X-ray diffraction. A new dinuclear 1,4-phenylene-bridged bisruthenium(II) complex, [1,4-{RuCl(eta(6)-C10H14)}(2){C-6(CH2NMe2)(4)-2,3,5,6-C,N,C',N'}] (9) has also been prepared from the dianionic ligand [C-6(CH2NMe2)(4)-2,3,5,6](2-) (C2N4). The C2N4 ligand is in an eta(2)-C,N-eta(2)-C',N'-bis(bidentate) bonding mode. Compound 9 does not isomerize in solution (halocarbon solvent), presumably because of the absence of an accessible C-aryl-H bond. Complex 9 could not be isolated in an analytically pure form, probably because of its high sensitivity to air and very low solubility, which precludes recrystallization.

Orotate complexes of rhodium(I) and iridium(I): effect of coligand, counter ion, and solvent of crystallisation on association via complementary hydrogen bonding

The new complexes [NEt3H][M(HL)(cod)] (M = Rh 1 or Ir 2; H3L = 2,6-dioxo-1,2,3,6-tetrahydropyrimidine-4-carboxylic acid, erotic acid; cod = cycloocta-1,5-diene) have been prepared by the reaction between [M2Cl2(cod)(2)] and erotic acid in dichloromethane in the presence of Ag2O and NEt3. They crystallise as dichloromethane adducts 1 . CH2Cl2 and 2 . CH2Cl2 from dichloromethane-hexane solutions. These isomorphous structures contain doubly hydrogen-bonded dimers, with additional hydrogen bonding to NEt3H+ cations and bridging CH2Cl2 molecules to form tapes. The use of (NBu4OH)-O-n instead of NEt3 gave the related complex [NBu4n][Rh(HL)(cod)] 1' which has an innocent cation not capable of forming strong hydrogen bonds and in contrast to 1 exists as discrete doubly hydrogen-bonded dimers. Complex 1' cocrystallises with 2,6-diaminopyridine (dap) via complementary triple hydrogen bonds to give [NBu4n][Rh(HL)(cod)]. dap . CH2Cl2 3. Complex 3 exhibits an extended sheet structure of associated [2 + 2] units, with layers of NBu4n, cations separating the sheets. These structural data together with those reported previously for platinum orotate complexes suggest that the steric requirements of the other ligands co-ordinated to the metal are important in influencing their hydrogen-bonding abilities. The solvent of crystallisation, the hydrogen-bonding propensity of the coligand and the nature of the counter ion also determine the type of association in the solid state.

Versatile N,C,N coordination behavior of a monoanionic aryldiamine ligand in ruthenium(II) complexes: Syntheses and crystal structures of [Ru-II(C6H3(CH(2)NMe(2))(2)-2,6)X(L)] (L equals norbornadiene, X=Cl, SO3CF3; L=PPh(3), X=I) and [Ru-II{C6H3(CH(2)NMe(2))(2)-2,6}(2,2':6:2''-terpyridine)]Cl

The monoanionic ligand [C6H3(CH(2)NMe(2))(2)-2,6](-), a potentially terdentate N,C,N bonding system, has been employed to synthesize a series of new ruthenium(II) complexes [Ru{C6H3(CH(2)NMe(2))(2)-2,6}X(L)] (L = PPh(3) X = Cl (2a), I (2b); L = norbornadiene (nbd), X = Cl (4), eta(1)-OSO2CF3 (5)) and [Ru{C6H3(CH(2)NMe(2))(2)-2,6}(2,2':6',2 ''-terpyridine)]Cl (3). X-ray crystal structures of 2b and 3-5 have been determined, in which the N,C,N coordination geometry with respect to the metal center is found to differ considerably. In each complex the aryldiamine ligand is terdentate, eta(3)-N,C,N-bonded as a six electron donor system. However, depending on the other ligands in the Ru(II) coordination sphere, this ligand demonstrates considerable flexibility in adopting coordination geometries which range from meridional in 3 through pseudomeridional in 2b to pseudofacial in 4 and 5. In the structures of 4 and 5 significant distortions of the aryl ring, involving bending of the six-membered ring into a boatlike conformation, are found. The different combinations of the N,C,N ligand with sets of other ligands lead to a range of metal geometries, i.e. square pyramidal in 2b, octahedral in 3, and bicapped tetrahedral in 4 and 5.

Long-range electronic coupling in bis(cyclometalated) ruthenium complexes

Symmetrical and unsymmetrical ligands containing terpyridyl coordinating units (N, N, N) or a cyclometalating equivalent (N, C, N), connected back-to-back either directly or via a p-terphenylene or 1,3-phenylene spacer, have been used to construct new diruthenium complexes. These compounds incorporate various terdentate chelates as capping ligands, to allow a double control of the electronic properties of each subcomplex and of the ensemble: via the terminal ligand or through the bridging fragment. Electronic coupling was studied from the intervalence transitions observed in several bimetallic ruthenium complexes of the bis-(cyclometalated) type differing by the substitution of a nitrogen atom by carbon in the terminal terpyridyl unit. The largest metal-metal interaction was found in complexes for which the terminal complexing unit is of the 1,3-di-2-pyridylbenzene type, i.e., with the carbon atom located on the metal-metal C-2 axis of the molecule. Investigations of the mechanism of interaction by extended Huckel calculations showed that the replacement of nitrogen by carbon raises the filled ligand levels, increasing the mixing with ligand orbitals and thus the metal-metal coupling. Finally, the intervalence transition was still observed for a bridging ligand containing three phenylene units as spacers, corresponding to a 24-Angstrom metal-metal distance.