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A three starting material four component reaction is developed for the synthesis of α,β-unsaturated ketones and β-amino ketones. TMEDA is used a dual synthon to provide two carbons in the Selectfluor system.

A base-induced synthesis of bicyclic 4-aminopyrimidines by the cycloaddition of three types of nitriles is reported. The scope of the method is demonstrated with 44 examples. Products are found to have luminescence properties and show potential applications as organic luminescent layer materials.

A novel, green and efficient method is developed for the synthesis of methylene bridged bis(indolyl)methanes in good to excellent yields. The reaction employs methyl tert-butyl ether (MTBE) as the methylene source and selectfluor as an oxidizing agent. The scope and versatility of the methods have been successfully demonstrated with 48 examples. The metal-free transformation process is suitable for scale-up production. A selectfluor-promoted oxidative reaction mechanism is proposed based on the results of the experimental studies.

A simple and green method is explored for the synthesis of fused pyridines by [2 + 2 + 1 + 1] the cycloaddition of ketones with an ammonium cation under a CO2 atmosphere. The reactions employed ammonium cation as a nitrogen source and CO2 gas as a carbon source in an aqueous solution. Monoethanolamine (MEA) was used as an additive to increase the solubility of CO2 in an aqueous solution. The scope and versatility of the method are demonstrated with 38 examples. Products are found to be photosensitive and show potential applications as organic optoelectronic materials. A selectfluor-promoted reaction mechanism is proposed based on the experimental studies. Our work is superior as it is a metal-free system, uses CO2 as a carbon source and MEA as an additive in aqueous synthesis.

A solvent-free method for the synthesis of quaternary ammonium salts (QAS) by iodoquaternization of alkenes with N-heteroarenes was reported. Its advantages lie in energy-saving and clean production by using iodine as the oxidant and manual grinding the starting materials, together with the complete atom economy and low process mass intensity (PMI) value. Demonstrated by 50 examples, the generated QAS was proved to be able to produce valuable chemicals, such as biological protease inhibitors, anti-cancer agents, and organic fluorescent materials.

A synthesis of azepines by the expansion of pyridine rings promoted by iodine in air is reported. The scope of the method is demonstrated with 27 examples. Two iodinations are involved in the reaction, in which the second iodination leads to the opening of the six-membered ring.

A three starting material four component reaction (3SM-4CR) is developed for the synthesis of α,β-unsaturated ketones and β-amino ketones in good yields. The reaction employs tetramethylethylenediamine (TMEDA) as a methylene and terminal olefin source, and Selectfluor as a mild oxidant. TMEDA worked as a dual synthon to provide two carbons in this metal-free transformation process. The scope and versatility of the methods have been demonstrated with 23 examples. A Selectfluor-promoted oxidative reaction mechanism is proposed based on the results of the experimental studies.

A series of β-enaminonitriles, 4-aminopyrimidines and 4-amidinopyrimidines were synthesized by condensation of organonitriles in one system. A wide variety of compounds were obtained in good to excellent yields by simply controlling the reaction temperature. The base-induced transformation process is easy for production. The scope and versatility of the method have been successfully demonstrated with 72 examples. The flexible and diversified characteristics of nitriles were introduced based on electronic effect, steric effect, position of substituted groups and intermolecular hydrogen bonding. An updated reaction mechanism is proposed based on the study of the stoichiometric reaction conditions at variable temperature, and on the investigation of products with cis–trans configuration transformation.

A copper(II)–hydroxide-induced carbon–carbon bond formation reaction is explored with the synthesis of an asymmetric carboxamido–methylimino pyridine Cu(I) complex of [CuI(py(N–CO)(NC–C)ph2Me2)2]− (12). Two imine-methyl groups are coupled to form a bridged C–C bond (NC–C–C–CN) at the methyl positions with the reduction of two Cu2+ center ions to Cu+. The reaction is checked with three dicarboxamido pyridine [CuII–OH] complexes, with which dinuclear Cu(I) complexes of [Cu2(py(N–CO)2ph2R2)2]2− (R = methyl (3), methyl and allyl (6)) and trinuclear [CuII–CuI–CuII] complex of [Cu3(⊂20-py(N–CO)2ph2dienMe3)2]+ (9) are obtained. The reactivities of the [CuII–L] (L = DMF, OH−) complexes in dicarboxamido pyridine, carboxamido–methylimino pyridine and dimethylimino pyridine systems are discussed in terms of the electron delocalization properties of ligands. A cooperative metal–ligand (Cu2+ and enamide ligand) interaction is proposed based on the characterization of ligated Cu(II) intermediates with the techniques of X-ray crystallography, UV-vis spectroscopy, cyclic voltammogram, EPR spectroscopy, and DFT calculations.

A novel, green and efficient method is developed for the synthesis of methylene bridged bis(indolyl)methanes in good to excellent yields. The reaction employs methyl tert-butyl ether (MTBE) as the methylene source and selectfluor as an oxidizing agent. The scope and versatility of the methods have been successfully demonstrated with 48 examples. The metal-free transformation process is suitable for scale-up production. A selectfluor-promoted oxidative reaction mechanism is proposed based on the results of the experimental studies.

A simple and efficient method is explored for the synthesis of 2-hydroxyimino-2-phenylacetonitriles (2) and phthalimides (4), by using nitromethane as nitrogen donors. Both reactions are promoted by Cu(II) system with the participation of dioxygen as an oxidant. The scope of the method has been successfully demonstrated with a total of 51 examples. The flexible and diversified characteristics of reactions are introduced in terms of electronic effect, steric effect, position of substituted groups, and intramolecular charge transfer. Experimental studies suggest that the methyl nitrite could be a precursor in the path to the final products. A possible reaction mechanism is proposed, including the Cu(II)/O2-facilitated transformation of nitromethane to methyl nitrite, the base-induced formation of 2-hydroxyimino-2-phenylacetonitriles, and the base-dioxygen-promoted formation of phthalimides.

A copper(ii)-hydroxide-induced carbon-carbon bond formation reaction is explored with the synthesis of an asymmetric carboxamido-methylimino pyridine Cu(i) complex of [CuI(py(N-C[double bond, length as m-dash]O)(N[double bond, length as m-dash]C-C)ph2Me2)2]- (12). Two imine-methyl groups are coupled to form a bridged C-C bond (N[double bond, length as m-dash]C-C-C-C[double bond, length as m-dash]N) at the methyl positions with the reduction of two Cu2+ center ions to Cu+. The reaction is checked with three dicarboxamido pyridine [CuII-OH] complexes, with which dinuclear Cu(i) complexes of [Cu2(py(N-C[double bond, length as m-dash]O)2ph2R2)2]2- (R = methyl (3), methyl and allyl (6)) and trinuclear [CuII-CuI-CuII] complex of [Cu3(⊂20-py(N-C[double bond, length as m-dash]O)2ph2dienMe3)2]+ (9) are obtained. The reactivities of the [CuII-L] (L = DMF, OH-) complexes in dicarboxamido pyridine, carboxamido-methylimino pyridine and dimethylimino pyridine systems are discussed in terms of the electron delocalization properties of ligands. A cooperative metal-ligand (Cu2+ and enamide ligand) interaction is proposed based on the characterization of ligated Cu(ii) intermediates with the techniques of X-ray crystallography, UV-vis spectroscopy, cyclic voltammogram, EPR spectroscopy, and DFT calculations.

A highly practical and economical method for the synthesis of 4-aminopyrimidines and β-enaminonitriles by condensation of mixed organonitriles is reported. Both reactions are promoted by lithium hexamethyldisilazide (LiHMDS). The metal-free transformation process is suitable for scale-up production. The influence of bases, solvents, and substituents on the aromatic rings is studied. The scope of the method has been successfully demonstrated with 58 examples. Mechanistic studies revealed the existence of β-enaminonitriles as intermediates to make 4-aminopyrimidines. A mechanism of the cycloaddition process is proposed including the production of β-enaminonitriles and 4-aminopyrimidines, respectively, by means of controlling reaction temperature.

An efficient and simple method was explored for the C–CN cleavage of acetonitrile in air at room temperature. The activation reaction was mediated by the mononuclear complex of [MII(PyN2Ph2Me2)(OH)]1− (M = Cu, Ni; PyN2Ph2Me2 = N,N′-bis(2,6-dimethylphenyl)-2,6-pyridinedicarboxamidate(2-)) in the presence of NaOH. Acetonitrile splits into cyanide and formaldehyde via the intermediate η2-enaminemethide isomer species of [MII–(CHCNH)] and [MII–(NCCH2)]. A base-dioxygen induced reaction mechanism was proposed based on the crystal structures of intermediate complexes and organic adducts, which were characterized by X-ray crystallography, EPR spectroscopy, GC-MS techniques and DFT calculations. The nitrile-activated product [CuII–CN] was utilized as a cyanide source for the catalytic cyanation of iodobenzene, phenylboronic acid and 2-phenylpyridine.

In biological imaging, the use of long-wavelength-emitting (>650 nm) fluorescent probes can significantly reduce the interference from cell auto-fluorescence and thus greatly improve the imaging resolution because intrinsic biomolecules rarely absorb light and emit fluorescence in the long-wavelength region. In this work, a long-wavelength-emitting two-photon fluorescent probe (TTNO) for nitric oxide (NO) detection in living cells is designed and synthesized. TTNO shows ∼28-fold enhanced fluorescence intensity (at 658 nm) with a low detection limit of 9 nM, a fast response to NO within ∼40 seconds and a high selectivity for NO. In addition, it is worth mentioning that TTNO can also be excited with near-infrared light via two-photon absorption. Its biological application for real-time imaging of exogenous and endogenous NO in living cells is successfully demonstrated by using one-photon and two-photon microscopy, respectively.

A highly simple and practical method was explored for the synthesis of pyridyl–pyrazole carboxylic compounds in one step by Cu(II) facilitated decarboxylation of 3,5-pyrazole-dicarboxylic acid (H3pdc) in pyridine–water. The activation of pyridine was induced by a hydroxyl radical, originating from the homolytic cleavage of the pz-COO− bond, and thereafter transfer of the radical to water. Mechanistic studies showed that the elongation of the CuII–Ocarboxyl bond in the side cores of [Cu3(pdc)2(py)6(H2O)2] (1) promoted the generation of reactive radicals through decarboxylation. A possible reaction mechanism was proposed, involving a radical-induced pyridine C–H bond activation and a copper-facilitated pyridyl–pyrazole C–N bond formation.

Various unsymmetrical aryl sulfides were synthesized by nickel-catalyzed C–S bond formation in good to excellent yields. The reactions employed arylsulfonyl chlorides as an aryl thiol source and Mn dust as a reducing agent. The scope and versatility of the method have been successfully demonstrated with 42 examples. Mechanistic studies revealed the existence of an intermediate disulfide substance. A catalytic cycle was proposed including a three-step reduction by Mn for the achievement of the reaction, and Ni(0) and Ni(I) species were supposed to be involved in the reaction mechanism.

A di-(2-pyridylmethyl)phenylamine ((PyCH2)2NPh) supported Cu(ii)/O2 catalytic system was explored with the synthesis of pyridylmethyl-based compounds of carboxylate (PyCOOH), amide (PyC(O)NHPh), and imine (PyCH[double bond, length as m-dash]NPh) from the oxidative N-dealkylation of N-(2-pyridylmethyl)phenylamine (PyCH2NHPh) and its derivatives, by means of controlling the addition of a base and/or water to the reaction system under a dioxygen atmosphere at room temperature. Experimental studies showed that the imine and amide species could be precursors in succession in the way to the final oxidation state of carboxylates. A cyclic catalytic mechanism was proposed including the base triggered C-H bond activation of the 2-pyridylmethyl group (PyCH2-) and the intermolecular Cu-OOH α-hydrogen atom abstraction from the coordinated imine substrate (PyCH[double bond, length as m-dash]NPh).

A dimeric tetranuclear carbonate-bridged Cu(II) complex [Cu4(DPA-iBu)4(μ2-CO3)2(MeOH)2]4 + 1 was prepared in-situ through oxidation of Cu(I) species by controlling the concentration of O2 in CO2. Lower concentration of O2 led to the formation of 1 after CO2 fixation but higher would give product as bis-μ2-hydroxo complex [Cu(DPA-iBu)(OH)]22 + 2, which was found to be an intermediate to generate trinuclear carbonated complex [Cu3(DPA-iBu)3(μ3-CO3)(MeCN)2(H2O)]4 + 3. The mechanism of this reaction was proposed and the nucleophilic attack of μ-peroxo Cu(II) species to CO2 molecules was suggested to be responsible for the generation of 1.

A singular feature of the catalytic C-cluster of carbon monoxide dehydrogenase is a sulfide-bridged Ni...Fe locus where substrate is bound and transformed in the reversible reaction CO + H(2)O right harpoon over left harpoon CO(2) + 2H(+) + 2e(-). A similar structure has been sought in this work. Mononuclear planar Ni(II) complexes [Ni(pyN(2)(Me2))L](1-) (pyN(2)(Me2) = bis(2,6-dimethylphenyl)-2,6-pyridinedicarboxamidate(2-)) derived from a NNN pincer ligand have been prepared including L = OH(-) (1) and CN(-) (7). Complex 1 reacts with ethyl formate and CO(2) to form unidentate L = HCO(2)(-) (5) and HCO(3)(-) (6) products. A binucleating macrocycle was prepared which specifically binds Ni(II) at a NNN pincer site and five-coordinate Fe(II) at a triamine site. The Ni(II) macrocyle forms hydroxo (14) and cyanide complexes (15) analogous to 1 and 7. Reaction of 14 with FeCl(2) alone and with ethyl formate and 15 with FeCl(2) affords molecules with the Ni(II)-L-Fe(II) bridge unit in which L = mu(2):eta(1)-OH(-) (17) and mu(2):eta(2)-HCO(2)(-) (18) and -CN(-) (19). All bridges are nonlinear (17, 140.0 degrees ; 18, M-O-C 135.9 degrees (Ni), 120.2 degrees (Fe); 19, Ni-C-N 170.3 degrees , Fe-N-C 141.8 degrees ) with Ni...Fe separations of 3.7-4.8 A. The Ni(II)Fe(II) complexes, lacking appropriate Ni-Fe-S cluster structures, are not site analogues, but their synthesis and reactivity provide the first demonstration that molecular Ni(II)...Fe(II) sites and bridges can be attained, a necessity in the biomimetic chemistry of C-clusters.

Four 2,5-pyridine dicarboxylate (pydc) metal (Mn, Mn/K, Zn, and Nd) coordination polymers with 2D and 3D architectures were synthesized, in which pydc ligand exhibits four new coordination modes to link up to seven metal atoms. Magnetic properties of the complexes are also discussed.

Solvothermal reaction of Mn(OAc)2 · 4H2O with 4,5-dicarboxyimidazole and phenanthroline resulted in a complex [Mn(phen)(Hdcbi)]n 1 in which Hdcbi as a μ2-bridge links two neighboring manganese(II) ions in chelating mode, forming one-dimensional zigzag chain framework. The fitting of magnetic data (J=−0.11 cm−1, zJ′=−0.06 cm−1, g=2.01) indicates weak antiferromagnetic coupling interactions between the Mn(II) sites.

Treatment of LZrCl2 (L - N, N'-ethylenebis(3,5-di-tert-butylsalicylideneiminato) (1), N, N'-o-phenylenebis(3,5-di-tert-butylsalicylideneiminato) (2)), which is an effective catalyst precursor for e ...

Two pyz complexes [Mn(pyz)(2)(H2O)(4)] (1) and [MnCl(pyz)(H2O)] (2) have been synthesized and structurally characterized. Complex 1 contains an eight-coordinate Mn(II) ion with square anti-prismati ...

Mono- and di-manganese inclusion compounds 1 and 2 are reported. Two mono-manganese molecules Mn(bpy)2(NO3)2 (bpy=2,2′-bipyridine) and [Mn(bpy)2(NO3)(H2O)]·NO3 coexist in the mole ratio of 1:1 in the structure of 1, while two di-manganese molecules [Mn2O(bpy)2(phtha)2(H2O)2]·(NO3)2 (phtha=phthalate) and [Mn2O(bpy)2(phtha)2(NO3)(H2O)]·NO3 in the structure of 2. Refluxing Mn(NO3)2/bpy/phthalic acid reaction mixtures in CH3CN leads to the isolation of 1, further concentration of the reaction solution in raising temperature results in 2. The Mn1 and Mn2 units in the inclusion compounds 1 and 2 are similar to other reported Mn1 and Mn2 analogs, respectively. The Jahn–Teller distortion was observed to give rise to the elongation along the OterminalMnOcarboxyl axes for all the four Mn(III) sites in 2, leading to unexpected longer Mn(III)Oaqua than Mn(II)Oaqua in 1. Extensive hydrogen bonding interactions among H2O, NO3 − and COOH were observed in the two inclusion compounds. Cyclic voltammetry of 2 in DMF displays two quasi-reversible redox couples at +0.10/+0.22 and −0.43/−0.36 V assigned to the Mn(III)Mn(IV)/2Mn(III) and 2Mn(III)/Mn(III)Mn(II), respectively. Variable temperature magnetic susceptibilities of 1 and 2 were measured. The data were fit to a model including axial zero-field splitting term and a good fit was found with D=1.77 cm−1, g=1.98 and F=1.48×10−5 for 1. For 2, the least-squares fitting of the experimental data led to J=2.37 cm−1, g=2.02 and D=0.75 cm−1 with R=1.45×10−3.

The mononuclear macrocyclic PdIIcomplexcis-[PdCl2([9]aneS3)] ([9]aneS3= 1,4,7-trithiacyclo-nonane) converts at 44 kbar into an intensely coloured chain polymer exhibiting distorted octahedral coordination at the metal centre and an unprecedented [1233] conformation for the thioether ligand. The evolution of an intramolecular axial sulfur–metal interaction and an intermolecular equatorial sulfur–metal interaction is central to these changes. High-pressure crystallographic experiments have also been undertaken on the related complexes [PtCl2([9]aneS3)], [PdBr2([9]aneS3)], [PtBr2([9]aneS3)], [PdI2([9]aneS3)] and [PtI2([9]aneS3)] in order to establish the effects of changing the halide ligands and the metal centre on the behaviour of these complexes under pressure. While all complexes undergo contraction of the various interaction distances with increasing pressure, only [PdCl2([9]aneS3)] undergoes a phase change. Pressure-induced I...I interactions were observed for [PdI2([9]aneS3)] and [PtI2([9]aneS3)] at 19 kbar, but the corresponding Br...Br interactions in [PdBr2([9]aneS3)] and [PtBr2([9]aneS3)] only become significant at much higher pressure (58 kbar). Accompanying density functional theory (DFT) calculations have yielded interaction energies and bond orders for the sulfur–metal interactions.

The title compound, [[Mn(C(4)H(4)O(6))(C(12)H(8)N(2))].6H(2)O](n), has a linear chain structure containing monomeric [Mn(C(4)H(4)O(6))(C(12)H(8)N(2))] repeat units. Each manganese ion is six-coordinate, with the two phenanthroline N atoms [Mn-N = 2.229 (2) and 2.235 (2) A] and four O atoms from two tartrate anions [Mn-O(COO) = 2.1252 (19) and 2.1310 (19) A, and Mn-O(OH) = 2.2404 (19) and 2.2424 (19) A] forming a seriously distorted octahedral coordination environment. Six water molecules exist outside every repeat unit as solvate molecules. Extensive hydrogen-bonding interactions and pi-pi stacking of the phenanthroline moieties exist between the chains.

The planar NNN-pincer complexes [M(II)(pyN(2)(Me2))(OH)](1-) (M(II) = Ni, Cu) fix CO(2) in η(1)-OCO(2)H complexes; results for the copper system are described. Mn(II), Fe(II), Co(II), and Zn(II) behave differently, forming [M(II)(pyN(2)(Me2))(2)](2-) with N(4)O(2) coordination. Incorporation of the Ni(II) pincer into binucleating macrocycle 2 containing a triamino M(II) locus connected by two 1,3-biphenylene groups affords proximal Ni(II) and M(II) sites for investigation of the synthesis, structure, and reactivity of Ni-X-M bridge units. This ligand structure is taken as a reference for variations in M(II) atoms and binding sites and bridges X = OH(-) and CN(-) to produce additional members of the macrocyclic family with improved properties. Macrocycle 2 with a 22-membered ring is shown to bind M(II) = Mn, Fe, and Cu with hydroxo bridges. Introduction of the 4-Bu(i)O group (macrocycle 3) improves the solubility of neutral complexes such as those with Ni(II)-OH-Cu(II) and Ni(II)-CN-Fe(II) bridges. Syntheses of macrocycle 5 with a 7-Me-[12]aneSN(3) and macrocycle 6 with a 1,8-Me(2)-[14]aneN(4) M(II) binding site are described together with hydoxo-bridged Ni/Cu and cyano-bridged Ni/Fe complexes. This work was motivated by the presence of a Ni···(HO)-Fe bridge grouping in a reactive state of carbon monoxide dehydrogenase. Attempted decrease in Ni-(OH)-M distances (3.70-3.87 Å) to smaller values observed in the enzyme by use of macrocycle 4 having 1,2-biphenylene connectors led to a mononuclear octahedral Ni(II) complex. Bridge structural units are summarized, and the structures of 14 macrocyclic complexes including 8 with bridges are described.

The crystal structure of the title compound, [Mn(C5H7O2)(C12H8N2)2](ClO4), contains a monomeric [Mn(phen)2(acac)]+ cation and a perchlorate anion [phen is 1,10′-phen­an­throline (C12H8N2) and acac is acetyl­acetonate (C5H7O2)]. The MnII ion is coordinated by four N atoms from the phen ligands [Mn—N 2.253 (4)–2.322 (4) A] and two O atoms of the acac ligand [Mn—O 2.116 (3) and 2.124 (3) A] in chelating mode, forming a distorted octahedral geometry.

The planar complexes [Ni(II)(pyN(2)(R2))(OH)](-), containing a terminal hydroxo group, are readily prepared from N,N'-(2,6-C(6)H(3)R(2))-2,6-pyridinedicarboxamidate(2-) tridentate pincer ligands (R(4)N)(OH), and Ni(OTf)(2). These complexes react cleanly and completely with carbon dioxide in DMF solution in a process of CO(2) fixation with formation of the bicarbonate product complexes [Ni(II)(pyN(2)(R2))(HCO(3))](-) having η(1)-OCO(2)H ligation. Fixation reactions follow second-order kinetics (rate = k(2)'[Ni(II)-OH][CO(2)]) with negative activation entropies (-17 to -28 eu). Reactions were monitored by growth and decay of metal-to-ligand charge-transfer (MLCT) bands at 350-450 nm. The rate order R = MemacroEtPr(i)Bu(i)Ph at 298 K (macro = macrocylic pincer ligand) reflects increasing steric hindrance at the reactive site. The inherent highly reactive nature of these complexes follows from k(2)' ≈ 10(6) M(-1) s(-1) for the R = Me system that is attenuated by only 100-fold in the R = Ph complex. A reaction mechanism is proposed based on computation of the enthalpic reaction profile for the R = Pr(i) system by DFT methods. The R = Et, Pr(i), and Bu(i) systems display biphasic kinetics in which the initial fast process is followed by a slower first order process currently of uncertain origin.

The Ni(II) complexes [Ni([9]aneNS(2)-CH(3))(2)](2+) ([9]aneNS(2)-CH(3)=N-methyl-1-aza-4,7-dithiacyclononane), [Ni(bis[9]aneNS(2)-C(2)H(4))](2+) (bis[9]aneNS(2)-C(2)H(4)=1,2-bis-(1-aza-4,7-dithiacyclononylethane) and [Ni([9]aneS(3))(2)](2+) ([9]aneS(3)=1,4,7-trithiacyclononane) have been prepared and can be electrochemically and chemically oxidized to give the formal Ni(III) products, which have been characterized by X-ray crystallography, UV/Vis and multi-frequency EPR spectroscopy. The single-crystal X-ray structure of [Ni(III)([9]aneNS(2)-CH(3))(2)](ClO(4))(6)·(H(5)O(2))(3) reveals an octahedral co-ordination at the Ni centre, while the crystal structure of [Ni(III)(bis[9]aneNS(2)-C(2)H(4))](ClO(4))(6)·(H(3)O)(3)·3H(2)O exhibits a more distorted co-ordination. In the homoleptic analogue, [Ni(III)([9]aneS(3))(2)](ClO(4))(3), structurally characterized at 30 K, the Ni-S distances [2.249(6), 2.251(5) and 2.437(2) A] are consistent with a Jahn-Teller distorted octahedral stereochemistry. [Ni([9]aneNS(2)-CH(3))(2)](PF(6))(2) shows a one-electron oxidation process in MeCN (0.2 M NBu(4)PF(6), 293 K) at E(½)=+1.10 V versus Fc(+)/Fc assigned to a formal Ni(III)/Ni(II) couple. [Ni(bis[9]aneNS(2)-C(2)H(4))](PF(6))(2) exhibits a one-electron oxidation process at E(½)=+0.98 V and a reduction process at E(½)=-1.25 V assigned to Ni(II)/Ni(III) and Ni(II)/Ni(I) couples, respectively. The multi-frequency X-, L-, S-, K-band EPR spectra of the 3+ cations and their 86.2% (61)Ni-enriched analogues were simulated. Treatment of the spin Hamiltonian parameters by perturbation theory reveals that the SOMO has 50.6%, 42.8% and 37.2% Ni character in [Ni([9]aneNS(2)-CH(3))(2)](3+), [Ni(bis[9]aneNS(2)-C(2)H(4))](3+) and [Ni([9]aneS(3))(2)](3+), respectively, consistent with DFT calculations, and reflecting delocalisation of charge onto the S-thioether centres. EPR spectra for [(61)Ni([9]aneS(3))(2)](3+) are consistent with a dynamic Jahn-Teller distortion in this compound.

Carbon dioxide may react with free or metal-bound hydroxide to afford products containing bicarbonate or carbonate, often captured as ligands bridging two or three metal sites. We report the kinetics and probable mechanism of an extremely rapid fixation reaction mediated by a planar nickel complex [Ni II (NNN)(OH)] 1- containing a tridentate 2,6-pyridinedicarboxamidate pincer ligand and a terminal hydroxide ligand. The minimal generalized reaction is M-OH + CO 2 → M-OCO 2 H; with variant M, previous rate constants are ≲10 3 M -1 s -1 in aqueous solution. For the present bimolecular reaction, the (extrapolated) rate constant is 9.5 × 10 5 M -1 s -1 in N,N′-dimethylformamide at 298 K, a value within the range of k cat / K M ≈10 5 –10 8 M -1 s -1 for carbonic anhydrase, the most efficient catalyst of CO 2 fixation reactions. The enthalpy profile of the fixation reaction was calculated by density functional theory. The initial event is the formation of a weak precursor complex between the Ni-OH group and CO 2 , followed by insertion of a CO 2 oxygen atom into the Ni-OH bond to generate a four center Ni( η 2 -OCO 2 H) transition state similar to that at the zinc site in carbonic anhydrase. Thereafter, the Ni-OH bond detaches to afford the Ni( η 1 -OCO 2 H) fragment, after which the molecule passes through a second, lower energy transition state as the bicarbonate ligand rearranges to a conformation very similar to that in the crystalline product. Theoretical values of metric parameters and activation enthalpy are in good agreement with experimental values [Δ H ‡ = 3.2(5) kcal/mol].

In the title compound, (C9H8N)[ZnCl3(C9H7N)], the ZnII atom is coordinated by three chloride ions and one N atom of the quinoline ligand to form a distorted tetrahedral coordination geometry, with a Zn—N bond length of 2.090 (4) A, Zn—Cl bond lengths ranging from 2.2319 (14) to 2.2707 (13) A and zinc bond angles ranging from 102.89 (11) to 115.41 (11)°.

In the title compound, [MnIII(salen)(OCOC3H2N2COOH)(H2O)]·H2O, (H2salen = N,N′-disalicyl­idene­ethyl­ene­di­amine, C16H14N2O2), two N and two O atoms from salen chelate to the MnIII ion, forming a distorted octahedral coordination sphere together with two other axial O atoms from a carboxyl group and a water mol­ecule. Extended intermolecular hydrogen bonds are observed to link the complex mol­ecules, forming a one-dimensional chain structure.

Pyridine-2,6-dimethanethiolate and pyridine-2,6-dithiocarboxylate form sparingly soluble Ni(II) pincer complexes formulated as [Ni(pdmt)](2) and [Ni(pdtc)](2), respectively, with two Ni-(mu(2)-S)-Ni bridges. In acetonitrile reaction systems, the latter undergoes the facile bridge cleavage reactions [Ni(pdtc)](2) + 2L(0,-) --> 2[Ni(pdtc)L](0,-) with an extensive set of nucleophiles to afford planar mononuclear products with L(-) = halide, CN, Me(3)SiO(-), RS(-) and L(0) = Et(3)P and a N-heterocyclic carbene. [Ni(pdmt)](2) is considerably less reactive toward bridge disruption. Cleavage products support several reactions of interest leading to other mononuclear species and to di- and trinuclear complexes. [Ni(pdtc)(OSiMe(3))](1-) deprotonates acetonitrile and acetone to form [Ni(pdtc)(CH(2)R)](1-) (R = CN, COMe). Reaction of [Ni(pdtc)SEt](1-) with Fe(II) yields the thiolate-bridged dimer {[Ni(pdtc)](2)(SEt)}(1-). Refluxing an acetonitrile solution of [Ni(pdtc)SH](1-) in air results in formation of trinuclear [Ni(pdtc)](3)S](2-) containing the rare unsupported Ni(3)(mu(3)-S) bridge core. Reaction of [Ni(pdtc)CN](1-) with [Fe(Me(6)tren)(OTf)](1+) forms the complex [Ni(pdtc)CNFe(Me(6)tren)](1+), the only example of a single Ni-C[triple bond]N-Fe bridge within a molecule. Structures of the various types of reaction products are presented. This work demonstrates the potential utility of bridge cleavage of polynuclear Ni(II) thiolates, an extensive family of compounds, to produce mononuclear products.

The structure of [Ag([18]aneS(4)O(2))](PF(6))(2).CH(2)Cl(2) shows a highly unusual and unexpected boat conformation for the macrocycle with square-planar S(4)-coordination at the formal Ag(ii) centre and the two ether O-centres lying on the same side of the S(4) plane; the SOMO in [Ag([18]aneS(4)O(2))](2+) possesses 22.7% Ag 4d(xy) character, as determined by multi-frequency EPR spectroscopy and supported by DFT calculations.

The mononuclear macrocyclic complexes [Au(I)([9]aneS2O)2]BF4 x MeCN 1a, [Au(II)([9]aneS2O)2](BF4)2 x 2 MeCN 2a, and [Au(III)([9]aneS2O)2](ClO4)6(H5O2)(H3O)2 3 ([9]aneS2O = 1-oxa-4,7-dithiacyclononane) have been prepared and structurally characterized by single crystal X-ray crystallography. The oxidation of [Au([9]aneS2O)2](+) to [Au([9]aneS2O)2](2+) involves a significant reorganization of the co-ordination sphere from a distorted tetrahedral geometry in [Au([9]aneS2O)2](+) [Au-S 2.3363(12), 2.3877(12), 2.6630(11), 2.7597(13) A] to a distorted square-planar co-ordination geometry in [Au([9]aneS2O)2](2+). The O-donors in [Au([9]aneS2O)2](2+) occupy the axial positions about the Au(II) center [Au...O = 2.718(2) A] with the S-donors occupying the equatorial plane [Au-S 2.428(8) and 2.484(8) A]. [Au([9]aneS2O)2](3+) shows a co-ordination sphere similar to that of [Au([9]aneS2O)2](2+) but with significantly shorter axial Au...O interactions [2.688(2) A] and equatorial Au-S bond lengths [2.340(4) and 2.355(6) A]. The cyclic voltammogram of 1 in MeCN (0.2 M NBu4PF6, 253 K) at a scan rate of 100 mV s(-1) shows an oxidation process at E(p)(a) = +0.74 V and a reduction process at E(p)(c) = +0.41 V versus Fc(+)/Fc assigned to the two-electron Au(III/I) couple and a second reduction process at E(p)(c) = +0.19 V assigned to the Au(I/0) couple. This electrochemical assignment is confirmed by coulometric and UV-vis spectroelectrochemical measurements. Multifrequency EPR studies of the mononuclear Au(II) complex [Au([9]aneS2O)2](2+) in a fluid solution at X-band and as frozen solutions at L-, S-, X-, K-, and Q-band reveal g(iso) = 2.0182 and A(iso) = -44 x 10(-4) cm(-1); g(xx) = 2.010, g(yy) = 2.006, g(zz) = 2.037; A(xx) = -47 x 10(-4) cm(-1), A(yy) = -47 x 10(-4) cm(-1), A(zz) = -47 x 10(-4) cm(-1); P(xx) = -18 x 10(-4) cm(-1), P(yy) = -10 x 10(-4) cm(-1), and P(zz) = 28 x 10(-4) cm(-1). DFT calculations predict a singly occupied molecular orbital (SOMO) with 27.2% Au 5d(xy) character, consistent with the upper limit derived from the uncertainties in the (197)Au hyperfine parameters. Comparison with [Au([9]aneS3)2](2+) reveals that the nuclear quadrupole parameters, P(ii) (i = x, y, z) are very sensitive to the nature of the Au(II) co-ordination sphere in these macrocyclic complexes. The observed geometries and bond lengths for the cations [Au([9]aneS2O)2](+/2+/3+) reflect the preferred stereochemistries of d(10), d(9), and d(8) metal ions, respectively, with the higher oxidation state centers being generated at higher anodic potentials compared to the related complexes [Au([9]aneS3)2](+/2+/3+).

Aggregation of tetranuclear Mn(4)O(2) building blocks with alkali ion was studied. Several Mn(iii) complexes containing [Mn(4)O(2)(AcO)(7)(pyz)(2)](-) (pyz = pyrazinate) anion(s) were obtained from an assembly system containing Mn(ii), MnO(4)(-), HOAc and Hpyz (Napyz or Kpyz). These [Mn(4)O(2)](8+) complexes have monomeric (1 and 2), dimeric (4 and 5) and one-dimensional chain () structures of which alkali metal ion connects the Mn ions of adjacent [Mn(4)O(2)](8+) units through mu(1,1)- and mu(1,3)-carboxylate bridges. Complexes 2 or 3 were converted into [Mn(12)O(12)(AcO)(16)(H(2)O)(4)] in EtOH solution in the presence of HOAc. However, in MeOH solution, a coordination polymer [Mn(2)(HCOO)(4)(H(2)O)(4)](n) was obtained accompanying the oxidation of MeOH to become HCHO and HCOOH. Tracing the (1)H NMR spectra of 2 or 3 in CD(3)OD, the disappearance of the resonance signals in 3 h indicated the decomposition of the [Mn(4)O(2)](8+) cores. Complex 2 exhibits its proton NMR signals in CDCl(3) which are similar to those of its pic analogue but accompany downfield shift to various extents for all the corresponding signals. Variable-temperature magnetic susceptibilities of complexes 2-5 in the range 5-300 K were recorded and were fitted for an Mn(4)O(2) butterfly core, giving the fitting parameters J(bb) = -2.67 to -3.76 cm(-1) and J(wb) = -1.16 to -3.14 cm(-1). Small J values indicate weak antiferromagnetic coupling interactions of the Mn(iii) sites and the spin ground states are considered as S(T) = 0 based on the J(bb)/J(wb) ratio approximately 1 for these complexes. The ESR spectra were recorded for complex 2 in dual-mode at liquid-helium temperatures and no obvious signal could be found. The addition of p-cresol gives rise to the reduction of the [Mn(4)O(2)](8+), resulting in observable signals.

The water-oxidizing complex (WOC) within photosystem II (PSII) can be reconstituted with synthetic manganese complexes by a process called photoactivation; however, the key factors affecting the efficiency of synthetic manganese complexes in reconstitution of electron transport and oxygen evolution activity in manganese-depleted PSII remain unclear. In the present study, four complexes with different manganese coordination environments were used to reconstitute the WOC, and an interesting relationship was found between the coordination environment of the manganese atom in the complexes and their efficiency in restoring electron transport and oxygen evolution. If Mn(II) is coordinated to nitrogen atoms within the ligand, it can restore significant rates of electron transport and oxygen evolution; however, if the manganese atom is coordinated only to oxygen atoms instead of nitrogen atoms, it has no capability to restore electron transport and oxygen evolution. So, our results demonstrate that the capability of manganese complexes to reconstitute the WOC is mainly determined by the coordination between nitrogen atoms from ligands and the manganese atom. It is suggested from our results that the ligation between the nitrogen atom and the manganese atom within the manganese complex facilitates the photoligation of the manganese atom to histidyl residues on the apo-protein in manganese-depleted PSII during photoactivation.

A reaction system consisting of terephthalic acid, NaOH, inorganic Mn(II) or Mn(III) salt, and salicylidene alkylimine resulted in dinuclear manganese complexes (salpn)(2)Mn(2)(mu-phth)(CH(3)OH)(2) (1, salpn = N,N'-1,3-propylene-bis(salicylideneiminato); phth = terephthalate dianion), (salen)(2)Mn(2)(mu-phth)(CH(3)OH)(2) (2, salen = N,N'-ethylene-bis(salicylideneiminato)), (salen)(2)Mn(2)(mu-phth)(CH(3)OH)(H(2)O) (3), and (salen)(2)Mn(2)(mu-phth) (4), while the absence of NaOH in the reaction led to a mononuclear Mn complex (salph)Mn(CH(3)OH)(NO(3)) (5, salph = N,N'-1,2-phenylene-bis(salicylideneiminato)). In addition, a trinuclear mixed metal complex H[Mn(2)Na(salpn)(2)(mu-OAc)(2)(H(2)O)(2)](OAc)(2) (6) was obtained from the reaction system by using maleic acid instead of terephthalic acid. Five-coordinate Mn ions were found in 4 giving rise to an intermolecular interaction and constructing a one-dimensional linear structure. Antiferromagnetic exchange interactions were observed for 1-3, and a total ferromagnetic exchange of 4 was considered to stem from intermolecular magnetic coupling. (1)H NMR signals of phenolate ring and alkylene (or phenylene) backbone of the diamine are similar to those reported in the literature, and the phth protons are at -2.3 to -10.1 ppm. Studies on structure, bond valence sum analysis, and magnetic properties indicate the oxidation states of the Mn ions in 6 to be +3, which are also indicated by ESR spectra in dual mode. Ferromagnetic exchange interaction between the Mn(III) sites was observed with J = 1.74 cm(-1). A quasireversible redox pair at -0.29V/-0.12V has been assigned to the redox of Mn(2)(III)/Mn(III)Mn(II), implying the intactness of the complex backbone in solution.

The title compound, [[Mn(C(4)H(4)O(6))(C(12)H(8)N(2))].6H(2)O](n), has a linear chain structure containing monomeric [Mn(C(4)H(4)O(6))(C(12)H(8)N(2))] repeat units. Each manganese ion is six-coordinate, with the two phenanthroline N atoms [Mn-N = 2.229 (2) and 2.235 (2) A] and four O atoms from two tartrate anions [Mn-O(COO) = 2.1252 (19) and 2.1310 (19) A, and Mn-O(OH) = 2.2404 (19) and 2.2424 (19) A] forming a seriously distorted octahedral coordination environment. Six water molecules exist outside every repeat unit as solvate molecules. Extensive hydrogen-bonding interactions and pi-pi stacking of the phenanthroline moieties exist between the chains.

The crystal structure of the title compound, [Mn(NO(3))(C(10)H(8)N(2))(H(2)O)(3)]NO(3), contains a monomeric [Mn(NO(3))(bpy)(H(2)O)(3)]+ cation (bpy is 2,2'-bipyridine) and a nitrate anion. The Mn(II) ion is coordinated by one chelating bpy [Mn-N 2.241 (3) and 2.259 (3) A], three water molecules [Mn-O 2.120 (3)-2.188 (3) A] and a nitrate ligand [Mn-O 2.228 (2) A] in a distorted octahedral geometry. There are O.H-O hydrogen-bonding interactions between the ligated water molecules and the ligated and unligated nitrate anions, resulting in double columns of stacked cations and anions.

The crystal structure of the title compound, [Mn(NO3)(C10H8N2)(H2O)3]NO3, contains a monomeric [Mn(NO3)(bpy)(H2O)3]+ cation (bpy is 2,2′-bi­pyridine) and a nitrate anion. The MnII ion is coordinated by one chelating bpy [Mn—N 2.241 (3) and 2.259 (3) A], three water mol­ecules [Mn—O 2.120 (3)–2.188 (3) A] and a nitrate ligand [Mn—O 2.228 (2) A] in a distorted octahedral geometry. There are O⋯H—O hydrogen-bonding interactions between the ligated water mol­ecules and the ligated and unligated nitrate anions, resulting in double columns of stacked cations and anions.