Trispyrazolylmethane piano stool complexes of iron(II) and cobalt(II)

A series of cationic trispyrazolylmethane complexes of the general form [Tm^RM(CH₃CN)₃]²⁺ (Tm = tris(pyrazolyl)methane, 1, R = 3,5-Me₂, M = Fe(II); 2, R = 3-Ph, M = Fe(II); 3, R = 3,5-Me₂, M = Co(II); 4, R = 3-Ph, M = Co(II)) with ‘piano-stool’ structures was prepared by the reaction of the N₃tripodal ligands (Tm^R)with [(CH₃CN)₆M](BF₄)₂ in a 1:1 stoichiometric ratio. Magnetic susceptibility measurements indicate that all four complexes with BF₄⁻ counter anions are paramagnetic, high-spin systems in the solid state with μ_eff at high temperatures of 5.2 (1, S = 2), 5.4 (2, S = 2), 4.9 (3, S = 3/2) and 4.6 (4, S = 3/2) BM, respectively. Comparisons of bond lengths from the metal centre to the Tm^R nitrogen donors, and from the metal centre to the acetonitrile nitrogen donors indicate that the neutral tripodal ligands appear to be more weakly coordinated to the metal centre than are the acetonitrile ligands. Reactions of these tripodal complexes with bidentate phosphine ligands, such as 1,2-diphosphinoethane or 1,2-bis(diallylphosphino)ethane leads to displacement of the tripodal ligand, or to the formation of more thermally stable bis-ligand complexes M(Tm^R)₂ (R = 3,5-dimethyl).     

Synthesis of water-soluble dinuclear metal complexes [metal = cobalt(II) and nickel(II)] and their behavior in solution

Two dinuclear metal complexes, [Co₂(bhmp)(MeCO₂)₂]ClO₄ · 2H₂O (1) and [Ni₂(bhmp)(MeCO₂)₂]ClO₄ · 2H₂O (2), were synthesized with a dinucleating ligand, 2,6-bis[bis(2-hydroxyethyl)aminomethyl]-4-methylphenol [H(bhmp)]. Both complexes were easily soluble in water as well as in DMF. Electronic spectra for both complexes were measured in both solvents and analyzed using the angular overlap model (AOM). From the electronic spectra and molar conductance, both complexes were determined to exist as [M₂(bhmp)(MeCO₂)₂]⁺ (M = Co^II or Ni^II) in DMF, dissociating perchlorate ions. On the other hand, in water, it was concluded that the acetate ions were partially dissociated and each complex existed as a mixture of some dissociated species, such as [M₂(bhmp)(MeCO₂)(H₂O)₂]²⁺ and [M₂(bhmp)(H₂O)₄]³⁺ (M = Co^II or Ni^II). Such dissociation was also confirmed by precipitation of the dissociated species when NaBPh₄ was added into an aqueous solution of the nickel complex.     

Electronic structure of [Ga2(tren)2(CAsq,cat)](BPh4)2(BF4): An EPR,ENDOR, and density functional study

The bimetallic [M₁M₂(tren)₂(CA^n?)]^m+ series, where M = Ga^III or Cr^III and CA is the chloranilate ligand which can take on diamagnetic (CA^cat,cat)^4? or paramagnetic (CA^sq,cat)^3? forms, comprises an electronically diverse series of compounds ranging from the closed-shell [Ga₂(tren)₂(CA^cat,cat)]²⁺ to the S = 5/2 ground state of [Cr₂(tren)₂(CA^sq,cat)]³⁺. This report deals with the interpretation of the EPR and ENDOR spectra of [Ga₂(tren)₂(CA^sq,cat)](BPh₄)₂(BF₄) (2) and the related derivative [Ga₂(tren)₂(DHBQ)](BPh₄)₂(BF₄) (2a) (where DHBQ is the fully deprotonated trianionic form of 2,5-dihydroxy-1,4-benzoquinone) in an effort to further characterize the electronic structure of this radical species. The X-band (～9.5 GHz) EPR spectrum of complex 2 acquired in a butyronitrile/propionitrile glass at 4 K reveals a rhombic g-tensor with g_xx = 2.0100, g_yy = 2.0097, and g_zz = 2.0060 with hyperfine interactions due to spin delocalization onto the two Ga nuclei (a_xx = 4.902 G, a_yy = 4.124 G, a_zz = 3.167 G); the origin of the hyperfine coupling was confirmed by analysis of the room temperature spectra of complexes 2 and 2a. The low-temperature spectrum of complex 2 also indicates the presence of a triplet electronic state characterized by a g-value of 2.009 and axial zero-field splitting of D = 150 G (0.012 cm^?1) as determined from measurements carried out at both X- and W-band (～95 GHz) frequencies. This triplet state is believed to arise due to a weak intermolecular Heisenberg exchange interaction between two aggregating complexes. ENDOR measurements on complex 2a at 20 K allowed for a determination of the magnitude of hyperfine coupling to the protons associated with the radical bridge as well as providing a rare example of an ENDOR signal arising from coupling to a gallium nucleus. Finally, these results were combined with literature data on the free semiquinone form of the bridging ligand in order to assess the extent to which density functional theory can predict unpaired spin density distribution in a complex molecule of this type. Although differences between theory and experiment were noted, DFT was able to provide a reasonably accurate picture of the electronic structure of this system as well as provide insight into the spin polarization mechanism(s) responsible for the observed hyperfine interactions.     

DNA binding and photocleavage properties and apoptosis-inducing activities of a ruthenium porphyrin complex [(Py-3′)TPP-Ru(phen)2Cl]Cl and its heterometallic derivatives

The interactions of a ruthenium porphyrin complex [(Py-3′)TPP-Ru(phen)₂Cl]Cl (phen = 1,10-phenanthroline, (Py-3′)TPP = 5-(3′-pyridyl-10,15,20-triphenylporphyrin) (1) and its heterometallic derivatives, [Ni(Py-3′)TPP-Ru(phen)₂Cl][PF₆] (2) and [Cu(Py-3′)TPP-Ru(phen)₂Cl][PF₆] (3), with calf thymus DNA have been investigated by spectroscopic and viscosity measurements in this study. The results showed that these synthetic complexes can bind to double strand helix DNA in groove binding mode, and the intrinsic binding constants of complexes 1, 2 and 3, as calculated according to the decay of the Soret absorption, are (1.35 ± 0.5) ×10⁵ M^?1 (s = 4.2), (1.29 ± 0.5) × 10⁵ M^?1 (s = 5.6) and (1.22 ± 0.5) × 10⁵ M^?1 (s = 6.2) (s is the binding-site size), respectively, which are consistent with those obtained from ethidium bromide-quenching experiments. Further investigations on the photocleavage properties of these complexes on plasmid pBR 322 DNA showed that complexes 1, 2 and 3 could cleave single chain DNA and convert DNA molecules from supercoiled form to the nicked form. As determined by MTT assay, the complexes were also identified as potent antiproliferative agents against A375 human melanoma cells, MCF-7 human breast adrenocarcinoma cells, Colo201 human colon adenocarcinoma cells and HepG2 human liver cancer cells. Complex 1 inhibits the growth of A375 cells through induction of apoptotic cell death and G0/G1 cell cycle arrest. Further investigation on intracellular mechanisms indicated that Complex 1 induced depletion of mitochondrial membrane potential (ΔΨ_m) in A375 cells through regulating the expression of pro-survival and pro-apoptotic Bcl-2 family members. Our results suggest that ruthenium porphyrin complexes could be candidates for further evaluation as chemopreventive and chemotherapeutic agents for human cancers.     

Synthesis,characterization and magnetic properties of six new copper(II) complexes with aminoacids as bridging ligand,exhibiting ferromagnetic coupling

The synthesis, crystallographic analysis and magnetic studies of six new copper(II) complexes of formulae [Cu(μ-ala)(im)(H₂O)]_n(ClO₄)_n (1), [Cu(μ-ala)(pz)(μ-ClO₄)] (2), [Cu(μ-phe)(im)(H₂O)]_n(ClO₄)_n (3), [Cu(μ-gly)(H₂O)(ClO₄)]_n (4), [Cu(μ-gly)(pz)(ClO₄)]_n(5) and [Cu(μ-pro)(pz)(ClO₄)]_n (6) have been carried out (ala = alanine; phe = phenylalanine; gly = glycine; pro = proline; im = imidazole; pz = pyrazole). In all cases, the deprotonated aminoacid ligand acts as chelate through the N(amine) and one O(carboxylato), whereas the second O atom of the same carboxylato acts as a bridge to the neighbouring copper(II) ion. The coordination of copper(II) ions is square-pyramidal in all complexes but 2 (elongated O_h). All complexes (1–6) are uniform chains with syn–anti (equatorial–equatorial) coordination mode of the carboxylato bridging ligand, exhibiting intrachain ferromagnetic interactions.     

Synthesis and structures of heterodinuclear organoplatinum(or -palladium)–molybdenum(or -tungsten) complexes: Unexpected structural deformation of heterodinuclear propionylplatinum–tungsten complex having 1,2-bis(diphenylphosphino)ethane ligand

Synthesis of a series of heterodinuclear phenylpalladium–molybdenum(or -tungsten) complexes having a bidentate nitrogen ligand, L₂PhPd–MCp(CO)₃ (M = Mo, L₂ = tmeda (12), bpy (13), phen (14); M = W, L₂ = tmeda (15)) by metathetical reactions of PdPhIL₂ with Na[MCp(CO)₃] and acylplatinum–molybdenum(or -tungsten) complex having a 1,2-bis(diphenylphosphino)ethane ligand, (dppe)(RCO)Pt–MCp(CO)₃ (M = Mo, R = Et (16), CH₂CMe₃ (18); M = W, R = Et (17)) by CO insertion into Pt–C bond in corresponding alkyl analogues (dppe)RPt–MCp(CO)₃ (M = Mo, R = Et (6), CH₂CMe₃, M = W, R = Et (8)) are described. These complexes are characterized by NMR and IR spectroscopies and elemental analyses, and the molecular structures of 12, 13, 17 and 18 are determined by X-ray structure analysis. The geometry at Pt (or Pd) is square planar and the MCp(CO)₃ moiety has three-leg piano-stool geometries in these complex expect the propionylplatinum–tungsten complex 17, which shows apparent but unexpected structural deformation at Pt and W, giving twisted square-planar and four-leg piano-stool geometries for platinum and tungsten, respectively.     

Syntheses,structures and properties of Zn(II) and Co(II) complexes of N-benzesulfonyl-l-glutamic acid ligand

The reaction of N-benzesulfonyl-l-glutamic acid (Bs-glu) with Zn(CH₃COO)₂ · 2H₂O or Co(CH₃COO)₂ · 4H₂O in the presence of imidazole (Im) produced two novel complexes [Zn(Im)₂(Bs-glu)]_n (1) and [Co(Im)₂(Bs-glu)]_n (2). Both of the complexes exhibit similar one-dimensional structural motif and coordination environment. Bs-glu adopts the bis-monodentated coordination mode linking two adjacent metal ions. The complex 1 shows intense photoluminescence in the solid state. Magnetic measurements for 2 show that the exchange interaction of the two Co(II) ions is antiferromagnetic.     

Synthesis,spectral and magnetical characterization of monomeric [Cu(2-NO2bz)2(3-pyme)2(H2O)2] and polymeric [Cu{3,5-(NO2)2bz}2(3-pyme)2]n

Two new complexes of composition [Cu(2-NO₂bz)₂(3-pyme)₂(H₂O)₂] (1) and/or [Cu{3,5-(NO₂)₂bz}₂(3-pyme)₂] (2) (3-pyme = 3-pyridylmethanol, ronicol or 3-pyridylcarbinol, 2-NO₂bz = 2-nitrobenzoate and 3,5-(NO₂)₂bz = 3,5-dinitrobenzoate) have been prepared and studied by elemental analysis, electronic, infrared and EPR spectroscopy, magnetic susceptibility measurements and the structure of both complexes has been solved. Complex (1) shows an unusual molecular type of structure consisting of the [Cu(2-NO₂bz)₂(3-pyme)₂(H₂O)₂] molecules held together by hydrogen bonds and van der Waals interactions. Complex (2) exhibits a polymeric chain-like structure [Cu{3,5-(NO₂)₂bz}₂(3-pyme)₂]_n with copper atoms doubly bridged by two 3-pyridylmethanol molecules and the polymeric molecules are held together by van der Waals interactions. Complex (1) exhibits a magnetic moment μ_eff = 1.84 B.M. at 300 K that remains nearly constant within the temperature region (5–300 K). Further cooling results in lowering the magnetic moment to μ_eff = 1.82 B.M. at 1.8 K. The magnetic susceptibility temperature dependence obeys Curie–Weiss law with Curie constant of 0.423 cm³ K mol⁻¹ and with Weiss constant of −0.06 K. The magnetic moment of (2) exhibits a small increase with a decrease in the temperature (μ_eff = 1.80 B.M. at 300 K and μ_eff = 1.85 B.M. at 1.8 K) with Curie constant of 0.409 cm³ K mol⁻¹ and with Weiss constant of +1.1 K, which can indicate a very weak ferromagnetic interaction between the copper atoms within the chain. Applying the molecular field model resulted in obtaining zJ′ values −0.08 cm⁻¹ for complex (1), and −0.07 cm⁻¹ for complex (2), respectively, that could characterize intermolecular and interchain interactions transmitted through π–π stacking.     

Synthesis,structures and magnetic properties of pentanuclear and trinuclear heterometallic complexes with bended and linear cyano-bridges (tren = tris(2-aminoethyl)amine)

The reaction of [Cu(tren)(OH₂)](ClO₄)₂ with KCN gave a mononuclear complex [Cu(tren)(CN)](ClO₄) (1) (tren = tris(2-aminoethyl)amine). Using 1 as a building block, one pentanuclear compound, [{Cu(tren)(NC)}₄Ni](ClO₄)₆ (2) and two trinuclear complexes, [{Cu(tren)NC}₂Co(tren)](ClO₄)₅ · 2H₂O (3), [{Cu(tren)CN}₂NiL](ClO₄)₄ (4) (L = 3,10-bis(2-hydroxyethyl)-1,3,5,8,10,12-hexaazacyclotetradecane) were prepared and characterized by single crystal X-ray analysis. In 1, Cu(II) atom adopts a distorted trigonal bipyramidal (TBP) geometry. In 2, the Ni(II) atom occupies the center of the pentanuclear compound with a square-planar coordination geometry. In 3, the six-coordinated Co(III) atom presents a distorted octahedral geometry with four nitrogen atoms from tren and two carbon atoms of bridged cyano groups in cis-positions. In 4, the nickel atom is located in an inversion center and coordinated with two [(tren)CuCN]⁺ moieties through cyano-bridging ligands. Magnetic susceptibility measurements of 2–4 show that the magnetic interactions between the heterometallic ions are antiferromagnetical coupling through the cyano bridges with g = 2.25, J = −0.142 cm⁻¹ and J′ = −0.167 cm⁻¹ for 2, g = 2.06, J = −0.094 cm⁻¹ for 3, and g = 2.20, J = −33.133 cm⁻¹ for 4. The correlations between the structures and the J values are discussed.     

Photophysical studies of hetero-bischelated complexes of rhodium(III) containing 2,2′-dipyridylamine

Four mixed-ligand complexes, cis-Rh[(bipy)(HDPA)Cl₂]Cl (1), cis-[Rh(phen)(HDPA)Cl₂]Cl (2), cis-[Rh(bipy)(DPA)Cl₂] (3), and cis-[Rh(phen)(DPA)Cl₂] (4) (where bipy = 2,2′-bipyridine, phen = 1,10-phenantroline, HDPA = 2,2′-dipyridylamine, and DPA = the deprotonated form of 2,2′-dipyridylamine) have been synthesized and characterized. In slightly acidic solution and at low temperature (77 K), both complexes 1 and 2 show a broad, symmetric and structureless red emission with microsecond lifetime identified as dd* phosphorescence. In slightly basic solution, the deprotonated complexes (3 and 4) exhibit a broad and asymmetric blue emission, showing no vibrational structure with a lifetime in the order of microseconds. Emission of complex 3 reveals a blue shift of 0.81 μm⁻¹ compared to the emission of complex 1 and that of complex 4 shows a blue shift of 0.77 μm⁻¹ with respect to complex 2. Electrochemical data have also been obtained for the four complexes in CH₃CN. There are two reduction peaks observed for both complexes 1 and 2. Each peak is followed by a one-electron reduction at the metal, with an elimination of chloride during each reduction step, which is in consistent with the dd* phosphorescence assignment for the two complexes. For complexes 3 and 4, only a one-electron reduction process occurs at the metal with an elimination of chloride. Based on the luminescence and electrochemical data, the emission of complexes 3 and 4 are assigned as πd* phosphorescence. Results from density functional theory (DFT) calculations provide theoretical evidence in support of this πd* assignments.     

Thermal decomposition studies of cis-bis(1-alkenyl)platinum(II) complexes

Thermal decomposition studies of bis(1-alkenyl)platinum(II) complexes of the type Pt(L₂)R₂ (where L = PPh₃ or L₂ = dppe or dppp; R = 1-alkenyl) are reported. The results revealed interesting organic product distributions depending on the length of the alkenyl chains, the nature of the supporting ligands and the metal centers. It is believed that the major decomposition pathways for the title complexes involve β-hydride elimination and/or reductive elimination as well as alkene isomerization. Mechanisms for the major and minor decomposition pathways are proposed. The amount of isomeric products obtained, i.e., 2-alkenes and 1,(n ? 2)-diene, increases with increasing chain length.     

Synthesis,crystal structures,DNA binding and cytotoxicity of two novel platinum(II) complexes containing 2-(hydroxymethyl)pyridine and pyridine-2-carboxylate ligands

Two new platinum(II) complexes, trans-[Pt(2-mpy)₂]·4H₂O (1) and [PtCl(2-pyc)(2-hmpy)]·H₂O (2), where 2-hmpy = 2-(hydroxymethyl)pyridine, 2-mpy = deprotonated 2-hmpy and 2-pyc = pyridine-2-carboxylate, have been synthesized and characterized by elemental analysis, IR, NMR, and X-ray crystallography. The DNA binding affinities of these complexes for Fish Sperm DNA (FS-DNA) were investigated using fluorescence, viscosity, thermal denaturation and gel electrophoresis measurements. Fluorescence analysis indicates that complex 1 binds to DNA by a single intercalative mechanism, while complex 2 exhibits two types of interactions such as intercalation and covalent binding. Gel electrophoresis assay demonstrates ability of the complexes to cleavage the supercoiled pBR322 plasmid DNA. The in vitro cytotoxicities of both complexes were preliminarily evaluated and the cytotoxicity of complex 1 against the human lung cancer cells (H1299) is similar to oxaliplatin, but higher than transplatin and carboplatin.     

A ratiometric fluorescent detection of Zn(II) in aqueous solutions using pyrene-appended histidine

A fluorescent chemosensor, Py-His, based on histidine was easily synthesized in solid phase synthesis. Py-His displayed a highly sensitive ratiometric response to Zn(II) with potent binding affinity (K_a = 1.17 × 10¹³ M^?2) in aqueous solutions. The detection limit of Py-His for Zn(II) was calculated as 80.8 nM. Moreover, Py-His distinguished Zn(II) and Hg(II) by different ratiometric response type; the chemosensor showed a more enhanced increase of excimer emission intensity to Zn(II) than Hg(II). Upon addition of Ag(I) and Cu(II), Py-His showed a turn-off response mainly due to the quenching effect of these metal ions. The binding stoichiometry (2:1 or 1:1) of Py-His to target metal ions played a critical role in the fluorescent response type (ratiometric and turn off response) to target metal ions. The role of imidazole group of Py-His for ratiometric detection of Zn(II) was proposed by pH titration experiments.     

Synthesis and antioxidant evaluation of (S,S)- and (R,R)-secoisolariciresinol diglucosides (SDGs)

Secoisolariciresinol diglucosides (SDGs) (S,S)-SDG-1 (major isomer in flaxseed) and (R,R)-SDG-2 (minor isomer in flaxseed) were synthesized from vanillin via secoisolariciresinol (6) and glucosyl donor 7 through a concise route that involved chromatographic separation of diastereomeric diglucoside derivatives (S,S)-8 and (R,R)-9. Synthetic (S,S)-SDG-1 and (R,R)-SDG-2 exhibited potent antioxidant properties (EC₅₀ = 292.17 ± 27.71 μM and 331.94 ± 21.21 μM, respectively), which compared well with that of natural (S,S)-SDG-1 (EC₅₀ = 275.24 ± 13.15 μM). These values are significantly lower than those of ascorbic acid (EC₅₀ = 1129.32 ± 88.79 μM) and α-tocopherol (EC₅₀ = 944.62 ± 148.00 μM). Compounds (S,S)-SDG-1 and (R,R)-SDG-2 also demonstrated powerful scavenging activities against hydroxyl [natural (S,S)-SDG-1: 3.68 ± 0.27; synthetic (S,S)-SDG-1: 2.09 ± 0.16; synthetic (R,R)-SDG-2: 1.96 ± 0.27], peroxyl [natural (S,S)-SDG-1: 2.55 ± 0.11; synthetic (S,S)-SDG-1: 2.20 ± 0.10; synthetic (R,R)-SDG-2: 3.03 ± 0.04] and DPPH [natural (S,S)-SDG-1: EC₅₀ = 83.94 ± 2.80 μM; synthetic (S,S)-SDG-1: EC₅₀ = 157.54 ± 21.30 μM; synthetic (R,R)-SDG-2: EC₅₀ = 123.63 ± 8.67 μM] radicals. These results confirm previous studies with naturally occurring (S,S)-SDG-1 and establish both (S,S)-SDG-1 and (R,R)-SDG-2 as potent antioxidants and free radical scavengers for potential in vivo use.     

Two new pseudohalide-bridged Cu(II) complexes with a hydrazone ligand: Syntheses,crystal structures and magnetic studies

Two new pseudohalide-bridged copper(II) complexes [{Cu(PBH)(μ_1,1-CNO)}₂] (1) and {Cu(PBH)(μ_1,5-NCNCN)}_n (2) (where HPBH = 2-pyridinecarboxaldehyde benzoyl hydrazone) have been synthesised and characterised by elemental analysis, CV, IR and UV–Vis spectral studies. The tridentate hydrazone pro-ligand (HPBH) was obtained by the condensation of benzhydrazide and pyridine-2-carboxaldehyde. Structures of both complexes have been established by X-ray crystallography which shows that 1 is a μ_1,1-CNO^?-bridged dimer whereas 2 is a μ_1,5-dca-bridged (dca = dicyanamide) linear polynuclear structure. Variable temperature magnetic susceptibility studies indicate weak antiferromagnetic interactions with J values ?0.50 cm^?1 and ?0.10 cm^?1 for 1 and 2, respectively.     

The effect of molecular packing on the occurrence of spin crossover phenomena in one-dimensional Fe(II)-bis-Schiff base complexes

Two new one-dimensional Fe(II)-bis-Schiff base complexes, [Fe(L1)(pyz)] · CH₂Cl₂ (1) and [Fe(L2)(pyz)] · 2CH₂Cl₂ (2) (H₂L1 = bis(O-vanillin)-O-phenylenediimine, H₂L2 = bis(O-vanillin)-2,3-naphthalenediimine, pyz = pyrazine) are reported with their crystal structures and magnetic property. Compound 1 shows a two-step SCO behavior while 2 shows HS at all the temperature range measured. Although the extension of aromatic moiety from benzene (L1) to naphthalene (L2) was introduced for the purpose of strengthening the cooperativity, it leads to the absence of SCO, due to the unanticipated π–π interaction, which leads to the longer Fe–N bond lengths and a weak ligand field around Fe(II) ion.     

Structure and catalytic activity of rhodium(I) carbene complexes in polymerization of phenylacetylene

Rh(I) carbene complexes of [RhX(bmim)(η⁴-1,5-cod)] type (bmim = 1-butyl-3-methyl imidazolium cation, X = Cl 2, Br 3, I 4), obtained in the reaction of [Rh(OMe)(η⁴-1,5-cod)]₂ (1) with [bmim]X ionic liquids, catalyzed polymerization of phenylacetylene (PA) to cis-polyphenylacetylene (PPA) in CH₂Cl₂ and in ionic liquids. The yield of PPA increased and molecular weight (M_w) decreased after addition of phosphorus ligands PPh₃ or P(OPh)₃. Complex 4 reacted with P(OPh)₃ giving cis-[RhI(bmim)(P(OPh)₃)₂] (5) complex which catalyzed oligomerization but not polymerization of PA.     

Ketone H2-hydrogenation catalysts: Ruthenium complexes with the headphone-like ligand bis(phosphaadamantyl)propane

Treatment of 1,3-diphosphinopropane with acetylacetone in the presence of HCl gives the new chiral bis(phosphaadamantyl)propane ligand (bpap) (1) as a mixture of diastereoisomers. Recrystallization from ethanol gives a mixture enriched in rac diastereoisomer (90% rac/10% meso). The enriched mixture reacts with [RuHCl(PPh₃)₃] in refluxing THF to give [RuHCl(bpap)(PPh₃)] (2) in 73% yield. Compound 2 reacts readily with chiral diamines giving octahedral trans-[RuHCl(bpap)(diamine)] complexes 3 (diamine = (1R,2R)-1,2-diaminocyclohexane) and 4 (diamine = (1R,2R)-1,2-diphenylethylenediamine). Compounds 3 and 4 are very active catalysts for H₂-hydrogenation of neat acetophenone in the presence of KO^tBu as a strong base under mild conditions (room temperature, 3 atm of H₂). The low ee values for 1-phenethanol can be attributed to the similar shapes of two terminal adamantoid cages and the flexible backbone of the bpap ligand. The structures of complexes 2 and 3 have been determined by single-crystal X-ray diffraction.     

New dinuclear cobalt(II) octaaza macrocyclic complexes with high oxidation redox potentials: Their crystal structure and unusual magnetic properties

Dinuclear cobalt(II) complexes were synthesised from 1,4,8,11-tetrakis-(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane (tmpc), [Co₂(tmpc)Cl₂][CoCl₄] (1), [Co₂(tmpc)Cl₂][PF₆]₂ (1a) and [Co₂(tmpc)(NO₃)₂][NO₃]₂ · MeOH (2) and characterised by magnetic, spectroscopic and electrochemical techniques and by single-crystal X-ray diffraction. The X-ray structures of 1 and 2 demonstrate that in both complexes the metal ion is exo-coordinated with respect to the macrocyclic ligand. In 1, the Co(II) ions are fivefold coordinated with trigonal bipyramidal geometry, while in 2 they are sixfold coordinated with a distorted octahedral geometry. The high magnetic moments obtained for these complexes are explained in terms of a spin–orbit coupling. Magnetic measurements show a deviation from the Curie–Weiss law at low temperatures. Two magnetic orderings were observed, at high temperatures an antiferromagnetic coupling was found, below 20 K a change to a weak ferromagnetic coupling was observed. Isothermal magnetic measurements at low temperature show a weak hysteresis, which was confirmed by the small coercive field found at low temperature. In addition, for the first time an explanation for the observation that these cobalt(II) compounds are very stable towards oxidation is offered in terms of the high redox potential values obtained for 1, 1a, and 2.