Metallic single-crystal CoSi nanowires via chemical vapor deposition of single-source precursor

We report the synthesis, structural characterization, and electrical transport properties of free-standing single-crystal CoSi nanowires synthesized via a single-source precursor route. Nanowires with diameters of 10-150 nm and lengths of greater than 10 mum were synthesized through the chemical vapor deposition of Co(SiCl(3))(CO)(4) onto silicon substrates that were covered with 1-2 nm thick SiO(2). Transmission electron microscopy confirms the single-crystal structure of the cubic CoSi. X-ray absorption and emission spectroscopy confirm the chemical identity and show the expected metallic nature of CoSi, which is further verified by room-temperature and low-temperature electrical transport measurements of nanowire devices. The average resistivity of CoSi nanowires is found to be about 510 muOmega cm. Our general and rational nanowire synthesis approach will lead to a broad class of silicide nanowires, including those metallic materials that serve as high-quality building blocks for nanoelectronics and magnetic semiconducting Fe(1-x)Co(x)Si suitable for silicon-based spintronics.     

Re-investigation of the thermal decomposition of Co(CO)4SiCl3 adsorbed on silica

Evidence is provided that thermal decomposition of Co(CO)(4)SiCl(3) adsorbed on silica in a hydrogen atmosphere results in the formation of metallic cobalt nanoparticles covered with a Co(2)SiO(4)/CoO shell instead of cobalt silicide nanoparticles, as had been reported previously.     

N-heterocyclic carbene stabilized dichlorosilylene transition-metal complexes of V(I), Co(I), and Fe(0)

Reactions of N-heterocyclic carbene stabilized dichlorosilylene IPr·SiCl(2) (1) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) with (η(5)-C(5)H(5))V(CO)(4), (η(5)-C(5)H(5))Co(CO)(2), and Fe(2)(CO)(9) afford dichlorosilylene complexes IPr·SiCl(2)·V(CO)(3)(η(5)-C(5)H(5)) (2), IPr·SiCl(2)·Co(CO)(η(5)-C(5)H(5)) (3), and IPr·SiCl(2)·Fe(CO)(4) (4), respectively. Complexes 2-4 are stable under an inert atmosphere, are soluble in common organic solvents, and have been characterized by elemental analysis and multinuclear ((1)H, (13)C, and (29)Si) NMR spectroscopy. Molecular structures of 2-4 have been determined by single crystal X-ray crystallographic studies and refined with nonspherical scattering factors.     

The bridged binding mode as a new, versatile template for the selective activation of carbon-fluorine bonds in fluoroolefins: activation of trifluoroethylene

We report the selective activation of carbon-fluorine bonds in trifluoroethylene using the diiridium complex [Ir(2)(CH(3))(CO)(2)(dppm)(2)][OTf] (1). Coordination of trifluoroethylene in a bridging position between the two metals in 1 results in facile fluoride ion loss in three different ways. Attack by strong fluorophiles such as Me(3)SiOTf and HOTf results in F(-) removal from one of the geminal fluorines to give the cis-difluorovinyl-bridged product [Ir(2)(CH(3))(OTf)(CO)(2)(μ-κ(1):η(2)-C(F)═CFH)(dppm)(2)][OTf]. A second activation can also be accomplished by addition of excess Me(3)SiOTf to give the fluorovinylidene-bridged product [Ir(2)(CH(3))(OTf)(CO)(2)(μ-C(2)FH)(dppm)(2)][OTf](2). Interestingly, activation of the trifluoroethylene-bridged precursor by water also occurs, yielding [Ir(2)(CH(3))(CO)(2)(κ(1)-C(H)═CF(2))(μ-OH)(dppm)(2)][OTf], in which the lone vicinal fluorine is removed, leaving a geminal arrangement of fluorines in the product. A [1,2]-fluoride shift can also be induced in the trifluoroethylene-bridged precursor upon the addition of CO to give the 2,2,2-trifluoroethylidene-bridged product [Ir(2)(CH(3))(CO)(3)(μ-C(H)CF(3))(dppm)(2)][CF(3)SO(3)]. Addition of hydrogen to the cis-difluorovinyl-bridged product results in the quantitative elimination of cis-difluoroethylene, while its reaction with CO yields a mixture of cis-difluoropropene and 2,3-difluoropropene by reductive elimination of the methyl and difluorovinyl groups with an accompanying isomerization in the case of the second product. Finally, protonation of the 2,2,2-trifluoroethylidene-bridged product liberates 1,1,1-trifluoroethane, in which one hydrogen (H(+)) is from the acid while the other hydrogen (H(-)) is derived from activation of the methyl group.     

Salts of the cobalt(I) complexes [Co(CO)5]+ and [Co(CO)2(NO)(2)]+ and the Lewis acid-base adduct [Co2(CO)7CO--B(CF3)3

The reaction of [Co(2)(CO)(8)] with (CF(3))(3)BCO in hexane leads to the Lewis acid-base adduct [Co(2)(CO)(7)CO--B(CF(3))(3)] in high yield. When the reaction is performed in anhydrous HF solution [Co(CO)(5)][(CF(3))(3)BF] is isolated. The product contains the first example of a homoleptic metal pentacarbonyl cation with 18 valence electrons and a trigonal-bipyramidal structure. Treatment of [Co(2)(CO)(8)] or [Co(CO)(3)NO] with NO(+) salts of weakly coordinating anions results in mixed crystals containing the [Co(CO)(5)](+)/[Co(CO)(2)(NO)(2)](+) ions or pure novel [Co(CO)(2)(NO)(2)](+) salts, respectively. This is a promising route to other new metal carbonyl nitrosyl cations or even homoleptic metal nitrosyl cations. All compounds were characterized by vibrational spectroscopy and by single-crystal X-ray diffraction.     

The synthesis, characterisation and reactivity of 2-phosphanylethylcyclopentadienyl complexes of cobalt, rhodium and iridium

2-Phosphanylethylcyclopentadienyl lithium compounds, Li[C(5)R'(4)(CH(2))(2)PR(2)] (R = Et, R' = H or Me, R = Ph, R' = Me), have been prepared from the reaction of spirohydrocarbons C(5)R'(4)(C(2)H(4)) with LiPR(2). C(5)Et(4)HSiMe(2)CH(2)PMe(2), was prepared from reaction of Li[C(5)Et(4)] with Me(2)SiCl(2) followed by Me(2)PCH(2)Li. The lithium salts were reacted with [RhCl(CO)(2)](2), [IrCl(CO)(3)] or [Co(2)(CO)(8)] to give [M(C(5)R'(4)(CH(2))(2)PR(2))(CO)] (M = Rh, R = Et, R' = H or Me, R = Ph, R' = Me; M = Ir or Co, R = Et, R' = Me), which have been fully characterised, in many cases crystallographically as monomers with coordination of the phosphorus atom and the cyclopentadienyl ring. The values of nu(CO) for these complexes are usually lower than those for the analogous complexes without the bridge between the cyclopentadienyl ring and the phosphine, the exception being [Rh(Cp'(CH(2))(2)PEt(2))(CO)] (Cp' = C(5)Me(4)), the most electron rich of the complexes. [Rh(C(5)Et(4)SiMe(2)CH(2)PMe(2))(CO)] may be a dimer. [Co(2)(CO)(8)] reacts with C(5)H(5)(CH(2))(2)PEt(2) or C(5)Et(4)HSiMe(2)CH(2)PMe(2) (L) to give binuclear complexes of the form [Co(2)(CO)(6)L(2)] with almost linear PCoCoP skeletons. [Rh(Cp'(CH(2))(2)PEt(2))(CO)] and [Rh(Cp'(CH(2))(2)PPh(2))(CO)] are active for methanol carbonylation at 150 degrees C and 27 bar CO, with the rate using [Rh(Cp'(CH(2))(2)PPh(2))(CO)] (0.81 mol dm(-3) h(-1)) being higher than that for [RhI(2)(CO)(2)](-) (0.64 mol dm(-3) h(-1)). The most electron rich complex, [Rh(Cp'(CH(2))(2)PEt(2))(CO)] (0.38 mol dm(-3) h(-1)) gave a comparable rate to [Cp*Rh(PEt(3))(CO)] (0.30 mol dm(-3) h(-1)), which was unstable towards oxidation of the phosphine. [Rh(Cp'(CH(2))(2)PEt(2))I(2)], which is inactive for methanol carbonylation, was isolated after the methanol carbonylation reaction using [Rh(Cp'(CH(2))(2)PEt(2))(CO)]. Neither of [M(Cp'(CH(2))(2)PEt(2))(CO)] (M = Co or Ir) was active for methanol carbonylation under these conditions, nor under many other conditions investigated, except that [Ir(Cp'(CH(2))(2)PEt(2))(CO)] showed some activity at higher temperature (190 degrees C), probably as a result of degradation to [IrI(2)(CO)(2)](-). [M(Cp'(CH(2))(2)PEt(2))(CO)] react with MeI to give [M(Cp'(CH(2))(2)PEt(2))(C(O)Me)I] (M = Co or Rh) or [Ir(Cp'(CH(2))(2)PEt(2))Me(CO)]I. The rates of oxidative addition of MeI to [Rh(C(5)H(4)(CH(2))(2)PEt(2))(CO)] and [Rh(Cp'(CH(2))(2)PPh(2))(CO)] are 62 and 1770 times faster than to [Cp*Rh(CO)(2)]. Methyl migration is slower, however. High pressure NMR studies show that [Co(Cp'(CH(2))(2)PEt(2))(CO)] and [Cp*Rh(PEt(3))(CO)] are unstable towards phosphine oxidation and/or quaternisation under methanol carbonylation conditions, but that [Rh(Cp'(CH(2))(2)PEt(2))(CO)] does not exhibit phosphine degradation, eventually producing inactive [Rh(Cp'(CH(2))(2)PEt(2))I(2)] at least under conditions of poor gas mixing. The observation of [Rh(Cp'(CH(2))(2)PEt(2))(C(O)Me)I] under methanol carbonylation conditions suggests that the rhodium centre has become so electron rich that reductive elimination of ethanoyl iodide has become rate determining for methanol carbonylation. In addition to the high electron density at rhodium.     

Fundamentals of melt infiltration for the preparation of supported metal catalysts. The case of Co/SiO2 for Fischer-Tropsch synthesis

We explored melt infiltration of mesoporous silica supports to prepare supported metal catalysts with high loadings and controllable particle sizes. Melting of Co(NO(3))(2)·6H(2)O in the presence of silica supports was studied in situ with differential scanning calorimetry. The melting point depression of the intraporous phase was used to quantify the degree of pore loading after infiltration. Maximum pore-fillings corresponded to 70-80% of filled pore volume, if the intraporous phase was considered to be crystalline Co(NO(3))(2)·6H(2)O. However, diffraction was absent in XRD both from the ordered mesopores at low scattering angles and from crystalline cobalt nitrate phases at high angles. Hence, an amorphous, lower density, intraporous Co(NO(3))(2)·6H(2)O phase was proposed to fill the pores completely. Equilibration at 60 °C in a closed vessel was essential for successful melt infiltration. In an open crucible, dehydration of the precursor prior to infiltration inhibited homogeneous filling of support particles. The dispersion and distribution of Co(3)O(4) after calcination could be controlled using the same toolbox as for preparation via solution impregnation: confinement and the calcination gas atmosphere. Using ordered mesoporous silica supports as well as an industrial silica gel support, catalysts with Co metal loadings in the range of 10-22 wt % were prepared. The Co(3)O(4) crystallite sizes ranged from 4 to 10 nm and scaled with the support pore diameters. By calcination in N(2), pluglike nanoparticles were obtained that formed aggregates over several pore widths, while calcination in 1% NO/N(2) led to the formation of smaller individual nanoparticles. After reduction, the Co/SiO(2) catalysts showed high activity for the Fischer-Tropsch synthesis, illustrating the applicability of melt infiltration for supported catalyst preparation.     

Sensitive and selective chromogenic sensing of carbon monoxide via reversible axial CO coordination in binuclear rhodium complexes

The study of probes for CO sensing of a family of binuclear rhodium(II) compounds of general formula [Rh(2){(XC(6)H(3))P(XC(6)H(4))}(n)(O(2)CR)(4-n)]·L(2) containing one or two metalated phosphines (in a head-to-tail arrangement) and different axial ligands has been conducted. Chloroform solutions of these complexes underwent rapid color change, from purple to yellow, when air samples containing CO were bubbled through them. The binuclear rhodium complexes were also adsorbed on silica and used as colorimetric probes for "naked eye" CO detection in the gas phase. When the gray-purple colored silica solids containing the rhodium probes were exposed to air containing increasing concentrations of CO, two colors were observed, in agreement with the formation of two different products. The results are consistent with an axial coordination of the CO molecule in one axial position (pink-orange) or in both (yellow). The crystal structure of 3·(CO) ([Rh(2){(C(6)H(4))P(C(6)H(5))(2)}(2)(O(2)CCF(3))(2)]·CO) was solved by single X-ray diffraction techniques. In all cases, the binuclear rhodium complexes studied showed a high selective response to CO with a remarkable low detection limit. For instance, compound 5·(CH(3)CO(2)H)(2) ([Rh(2){(m-CH(3)C(6)H(3))P(m-CH(3)C(6)H(4))(2)}(2)(O(2)CCH(3))(2)]·(CH(3)CO(2)H)(2)) is capable of detection of CO to the "naked eye" at concentrations as low as 0.2 ppm in air. Furthermore, the binding of CO in these rhodium complexes was found to be fully reversible, and release studies of carbon monoxide via thermogravimetric measurements have also been carried out. The importance of the silica support for the maintenance of the CO-displaced L ligands in the vicinity of the probes in a noninnocent manner has been also proved.     

Surface Organometallic Chemistry on Oxides: Reaction of Trimethylphosphine with Bis(allyl)rhodium Grafted onto Silica

The reaction of Rh(eta(3)-C(3)H(5))(3) with the surface hydroxyl groups of partially dehydroxylated silica leads to the formation of the surface organometallic complex (&tbd1;SiO)(&tbd1;SiOX)Rh(eta(3)-C(3)H(5))(2), 1 (where X is H or Si&tbd1;), with evolution of propene. The reaction of 1 with PMe(3) was examined, and two major pathways were discovered. Reductive elimination of two allyl ligands as 1,5-hexadiene and coordination of PMe(3) give the surface product (&tbd1;SiO)Rh(PMe(3))(3), 2, which was characterized by elemental analysis, IR and (31)P MAS NMR spectroscopy. We also prepared 2 independently from CH(3)Rh(PMe(3))(3) and partially dehydroxylated silica. The second major reaction pathway is the elimination of propene to give (&tbd1;SiO)(2)Rh(eta(1)-C(3)H(5))(PMe(3))(3), 3. The presence of the sigma-bound allyl ligand was inferred from its characteristic IR spectrum. The reactivity of 3 toward CO was examined: insertion of CO into the Rh-C bond followed by reductive elimination of the silyl ester &tbd1;SiOC(O)C(3)H(5) produces (&tbd1;SiO)Rh(CO)(PMe(3))(2), 4. In static vacuum, 3 decomposes to give allyl alcohol, which is slowly decarbonylated by 2.     

Thermal stability of organic monolayers chemically grafted to minerals

The thermal degradation of monolayers of alkylsilicon hydrides (RSiH(3)), alkylphosphonic acids (RP(O)(OH)(2)), and alkyldimethylchlorosilanes (R(CH(3))(2)SiCl) supported on silica, alumina, titania, zirconia, and calcium hydroxyapatite particles was investigated using thermal gravimetric analysis (TGA). The common feature in the TGA was a dramatic weight loss between approximately 200 and approximately 600 degrees C (N(2) atmosphere), which was not present for bare minerals, and, thus, was assigned to the degradation of the surface grafted organic species. The onset of weight loss and the temperature of maximal weight loss rate (T(MAX)) showed no dependence on the mineral and were determined by the nature of the chemical group directly attached to the surface. The T(MAX) values were approximately 400-450 degrees C (monolayers of RSiH(3) and RP(O)(OH)(2)) and approximately 250 degrees C (monolayers of RSi(CH(3))(2)Cl). The activation energies (E(A)) of the degradation processes were determined using TGA at multiple heating rates. Surprisingly, the substrate material did not show a significant effect on E(A). For example, all the monolayers of octadecyl groups (R=C(18)H(37)) supported on silica, alumina, titania, and zirconia showed closed E(A) values approximately 265+/-15 kJ/mol. The weight loss, IR, MS, and chemical analysis data suggested that monolayer degradation occurred through pyrolysis of the hydrocarbon moieties (R groups) via cleavage of the CC and SiC (monolayers of silanes) or CC and PC bonds (monolayers of phosphonic acids). The inorganic portion of the molecule remained attached to the surface of the mineral (presumably as silicates or phosphates).     

Diastereoselective formation of 5-vinylcyclopentenes from 1, 6-enynes: cobalt-mediated C-H allylic activation and formal 5-endo-Dig cyclization

A novel intramolecular cyclization reaction mediated by dicobalt octacarbonyl (Co(2)(CO)(8)) is reported. Thermolysis in an argon atmosphere transforms the cobalt complex of 1-trimethylsilyl-6-hepten-1-ynes into 1-trimethylsilyl-5-vinylcyclopentenes in good yield and in a highly diastereoselective manner. This formal 5-endo-dig cyclization is proposed to proceed via an allylic C-H oxidative addition.     

Synthesis and characterization of a new family of square-planar nickel(II) carbonyl derivatives

The reaction of [NBu(4)](2)[Ni(C(6)F(5))(4)] (1) with solutions of dry HCl(g) in Et(2)O results in the protonolysis of two Nibond;C(6)F(5) bonds giving [NBu(4)](2)[[Ni(C(6)F(5))(2)](2)(mu-Cl)(2)] (2 a) together with the stoichiometrically required amount of C(6)F(5)H. Compound 2 a reacts with AgClO(4) in THF to give cis-[Ni(C(6)F(5))(2)(thf)(2)] (3). Reacting 3 with phosphonium halides, [PPh(3)Me]X, gives dinuclear compounds [PPh(3)Me](2)[[Ni(C(6)F(5))(2)](2)(mu-X)(2)] (X=Br (2 b) or I (2 c)). Solutions of compounds 2 in CH(2)Cl(2) at 0 degrees C do not react with excess CNtBu, but do react with CO (1 atm) to split the bridges and form a series of terminal Ni(II) carbonyl derivatives with general formula Qcis-[Ni(C(6)F(5))(2)X(CO)] (4). The nu(CO) stretching frequencies of 4 in CH(2)Cl(2) solution decrease in the order Cl (2090 cm(-1))>Br (2084 cm(-1))>I (2073 cm(-1)). Compounds 4 revert to the parent dinuclear species 2 on increasing the temperature or under reduced CO pressure. [NBu(4)]cis-[Ni(C(6)F(5))(2)Cl(CO)] (4 a) reacts with AgC(6)F(5) to give [NBu(4)][Ni(C(6)F(5))(3)(CO)] (5, nu(CO)(CH(2)Cl(2))=2070 cm(-1)). Compound 5 is also quantitatively formed ((19)F NMR spectroscopy) by 1:1 reaction of 1 with HCl(Et(2)O) in CO atmosphere. Complex 3 reacts with CO at -78 degrees C to give cis-[Ni(C(6)F(5))(2)(CO)(2)] (6, nu(CO)(CH(2)Cl(2))=2156, 2130 cm(-1)), which easily decomposes by reductive elimination of C(6)F(5)bond;C(6)F(5). Compounds 3 and 6 both react with CNtBu to give trans-[Ni(C(6)F(5))(2)(CNtBu)(2)] (7). The solid-state structures of compounds 3, 4 b, 6, and 7 have been established by X-ray diffraction methods. Complexes 4-6 are rare examples of square-planar Ni(II) carbonyl derivatives.     

Synthesis and reactivity of molybdenum and tungsten bis(dinitrogen) complexes supported by diphosphine chelates containing pendant amines

Molybdenum and tungsten bis(dinitrogen) complexes of the formula M(N(2))(2)(PNP)(2) (M = Mo and W) and W(N(2))(2)(dppe)(PNP), supported by diphosphine ligands containing a pendant amine of the formula (CH(2)PR(2))(2)NR' = P(R)N(R')P(R) (R = Et, Ph; R' = Me, Bn), have been prepared by Mg reduction of metal halides under an N(2) atmosphere. The complexes have been characterized by NMR and IR spectroscopy, X-ray crystallography, and cyclic voltammetry. Reactivity of the target Mo and W bis(dinitrogen) compounds with CO results in the formation of dicarbonyl complexes.     

Syntheses of 8-quinolinolatocobalt(III) complexes containing cyclen based auxiliary ligands as models for hypoxia-activated prodrugs

New ligands H(2)L2-H(2)L6 comprise the cyclen macrocycle which is N,N'-dialkylated at the 1,7-nitrogen atoms by three- and four-carbon alkyl chains bearing terminal sulfonic (C(3) H(2)L2), phosphonic (C(3) H(2)L3, C(4) H(2)L4) or carboxylic acid (C(3) H(2)L5, C(4) H(2)L6) groups, and HL7 is N-monoalkylated by a four-carbon sulfonic acid group. The ligands were prepared by alkylation of a bridged bisaminal intermediate. The syntheses of cobalt(III) complexes containing a tetradentate cyclen, N,N'-1,7-Me(2)cyclen, cyclam or L2-L7 ligand together with the bidentate 8-quinolinato (8QO(-)) ligand, of interest as it is a model for a more potent cytotoxic analogue, were investigated. Coordination of ligands (L) cyclen, N,N'-1,7-Me(2)cyclen or cyclam to cobalt(III) was achieved using Na(3)[Co(NO(6))] to form [Co(L)(NO(2))(2)](+). HOTf (trifluoromethansulfonic acid) was used to prepare the triflato complexes [Co(L)(OTf)(2)](+), followed by substitution of the labile triflato ligands to yield [Co(L)(8QO)](ClO(4))(2) isolated as the perchlorate salts. One further example containing cyclam and the 5-hydroxymethyl-8-quinolinato ligand was also prepared by this method. Complexes containing the pendant arm ligands L2-L6 were prepared from the cobalt precursor trans-[Co(py)(4)Cl(2)](+). Reaction of this complex with H(2)L2·4HCl and 8QOH produced [Co(L2)(8QO)] in one step and contains two deprotonated sulfonato pendant arms. The reaction of H(2)L3·4HBr with [Co(py)(4)Cl(2)](+) gave [Co(L3)]Cl in which L3 acts as a hexadenate ligand with the three-carbon phosphonato side chains coordinated to cobalt. H(2)L5·4HCl bearing three-carbon carboxylic acid pendant arms gave a similar result. The four-carbon ligands were coordinated to cobalt by reaction of [Co(py)(4)Cl(2)](+) with H(2)L4·4HBr or H(2)L6·4HCl to give [Co(HL4)Cl(2)] or [Co(H(2)L6)Cl(2)]Cl, which in turn with 8QOH gave the 8QO(-) complexes [Co(L4)(8QO)] bearing anionic phosphate pendant arms or [Co(H(2)L6)(8QO)]Cl(2) containing neutral carboxylic acid side chains. The reaction of Na(3)[Co(CO(3))(3)] with the mono-N-alkylated ligand HL7·4HCl and then HOTf gave [Co(L7)(CO(3))] and then in turn [Co(L7)(OTf)(2)]. The carbonato complex [Co(L7)(CO(3))] with [8QO](2)[SO(4)] produced [Co(L7)(CO(3))]. All complexes containing L7 bear an anionic sulfonato group on the side chain. The synthesis and characterisation of the six new ligands based on N-alkylated cylen ligand and the cobalt complexes outlined above are described, along with cyclic voltammograms of the 8QO(-) complexes and the molecular structures determined by X-ray crystallography of [Co(cyclen)(H(2)O)(2)](OTf)(3) (formed by aquation of the triflato complex), [Co(cyclen)(8QO)](ClO(4))(2), Co(L2)(8QO)·2H(2)O, Co(L4)(8QO)·6H(2)O and [Co(H(2)L6)Cl(2)]Cl·H(2)O. These demonstrate the coordination of the cyclen ligand in the folded anti-O,syn-N configuration with the N-alkylated nitrogens occupying apical positions.     

New dirhenium(III) compounds bridged by carboxylate ligands: N(C(4)H(9))(4)[Re(2)(OOCCF(3))Cl(6)] and Re(2)(OOCCCHCo(2)(CO)(6))(4)Cl(2)

The solvothermal reaction of (N(C(4)H(9))(4))(2)[Re(2)Cl(8)] with trifluoroacetic acid and acetic anhydride leads to the new rhenium trifluoroacetate dimer N(C(4)H(9))(4)[Re(2)(OOCCF(3))Cl(6)] (1) and to the rhenium carbonyl dimer Re(2)(mu(2)-Cl)(2)(CO)(8) as the rhenium-reduced byproduct. The reaction of the precursor complex, N(C(4)H(9))(4)[Re(2)(OOCCF(3))Cl(6)] (1), with the organometallic carboxylic acid (CO)(6)Co(2)HCCCOOH leads to the cluster of clusters compound Re(2)(OOCCCHCo(2)(CO)(6))(4)Cl(2) (2), which has the dimer structure of Re(2)(OOCR)(4)Cl(2). Cyclic voltammetric measurements show that Re(2)(OOCCCHCo(2)(CO)(6))(4)Cl(2) (2) has one reduction centered on the dirhenium core and a reduction centered on the cobalt atoms. DFT calculations have been used to rationalize the observed displacements of the voltammetric signals in Re(2)(OOCCCHCo(2)(CO)(6))(4)Cl(2) (2) compared to the parent ligand (CO)(6)Co(2)HCCCOOH and rhenium pivalate.     

Transition metal containing decatungstosilicate dimer [M(H(2)O)(2)(gamma-SiW(10)O(35))(2)](10-) (M = Mn(2+), Co(2+), Ni(2+))

The new, monometal substituted silicotungstates [Mn(H(2)O)(2)(gamma-SiW(10)O(35))(2)](10-) (1), [Co(H(2)O)(2)(gamma-SiW(10)O(35))(2)](10-) (2) and [Ni(H(2)O)(2)(gamma-SiW(10)O(35))(2)](10-) (3) have been synthesized and isolated as the potassium salts K(10)[Mn(H(2)O)(2)(gamma-SiW(10)O(35))(2)] x 8.25 H(2)O (K-1), K(10)[Co(H(2)O0(2)(gamma-SiW(10)O(35))(2)] x 8.25 H(2)O (K-2) and K(10)[Ni(H(2)O)(2)(gamma-SiW(10)O(35))(2)] x 13.5 H(2)O (K-3), which have been characterized by IR spectroscopy, single crystal X-ray diffraction, elemental analysis and cyclic voltammetry. Polyanions 1-3 are composed of two (gamma-SiW(10)O(36)) units fused on one side via two W-O-W' bridges and on the other side by an octahedrally coordinated trans-MO(4)(OH(2))(2) transition metal fragment, resulting in a structure with C(2v) point group symmetry. Anions 1-3 were synthesized by reaction of the dilacunary precursor [gamma-SiW(10)O(36)](8-) with Mn(2+), Co(2+) and Ni(2+) ions, respectively, in 1 M KCl solution at pH 4.5. The electrochemical properties of 1-3 were studied by cyclic voltammetry and controlled potential coulometry in a pH 5 buffer medium. The waves associated with the W-centers are compared with each other and with those of the parent lacunary precursor [gamma-SiW(10)O(36)](8-) in the same medium. They appear to be dominated by the acid-base properties of the intermediate reduced species. A facile merging of the waves for 3 is observed while those for 1 and 2 remain split. Controlled potential coulometry of the single wave of 3 or the combined waves of 1 and 2 is accompanied by catalysis of the hydrogen evolution reaction. No redox activity was detected for the Ni(2+) center in 3, whereas the Co(2+) center in 2 shows a one-electron redox process. The two-electron, chemically reversible process of the Mn(2+) center in 1 is accompanied by a film deposition on the electrode surface.     

Cubic and rhombohedral heterobimetallic networks constructed from uranium, transition metals, and phosphonoacetate: new methods for constructing porous materials

Four heterobimetallic U(vi)/M(ii) (M = Mn, Co, Cd) carboxyphosphonates have been synthesized. M(2)[(UO(2))(6)(PO(3)CH(2)CO(2))(3)O(3)(OH)(H(2)O)(2)]·16H(2)O (M = Mn(ii), Co(ii), and Cd(ii)) adopt cubic three-dimensional network structures with large cavities approximately 16 ? in diameter that are filled with co-crystallized water molecules. [Cd(3)(UO(2))(6)(PO(3)CH(2)CO(2))(6)(H(2)O)(13)]·6H(2)O forms a rhombohedral channel structure with hydrated Cd(ii) within the channels. The cubic compound (Co) displays differential gas absorption with a surface area for CO(2) uptake of 40 m(2) g(-1) at 273 K, and no uptake of N(2) at 77 K.     

Silver cages with encapsulated acetylenediide as building blocks for hydrothermal synthesis of supramolecular complexes with n-cyanopyridine and pyridine-n-carboxamide (n=3, 4)

New silver(i) double salts (Ag(2)C(2))(AgCF(3)CO(2))(8)(3-pyCONH(2))(2)(H(2)O)(4) (1), [(Ag(2)C(2))(AgCF(3)CO(2))(4)(4-pyCONH(2))(H(2)O)].H(2)O (2), (Ag(2)C(2))(AgCF(3)CO(2))(6)(3-pyCONH(2))(4) (3), (Ag(2)C(2))(AgCF(3)CO(2))(6)(3-pyCN)(2) (4) and (Ag(2)C(2))(AgCF(3)CO(2))(4)(4-pyCN)(2) (5) (n-pyCONH(2) is pyridine-n-carboxamide, n-pyCN is n-cyanopyridine; n=3, 4) have been synthesized by the hydrothermal method. All five compounds contain polyhedral silver(i) cages each encapsulating a C(2)(2-) dianion. Compounds 1, 3 ,4 and 5 exhibit three-dimensional structures, whereas compound 2 is a two-dimensional network. The structure of 1 is constructed from the linkage of a branched-tree architecture via hydrogen bonds. Unlike 4 and 5, which involve the connection of n-cyanopyridine (n=3, 4) with silver columns, 3 results from the linkage of discrete silver cages via pyridine-3-carboxamide.     

A general method for preparation of metal carbenes via solution- and polymer-based approaches

A new general, synthetically simple, and safe method for the preparation of metal carbene complexes, which is based on diphenyl sulfonium salts as carbenoid precursors, has been developed, and its scope and applications were studied. In general, deprotonation of a sulfonium salt with a base results in a sulfur ylide, which, in turn, reacts with an appropriate metal precursor to give the corresponding metal carbene complex. Thus, starting from benzyldiphenylsulfonium salt, the complexes (PCX)Rh=CHPh (X = P, N) were prepared in quantitative yield. Syntheses of Grubbs' catalyst, (PCy(3))(2)Cl(2)Ru=CHPh, and of Werner's carbene, [Os(=CHPh)HCl(CO)(P(i)Pr(3))(2)], were achieved by this method. Novel trans-bisphosphine Rh and Ir carbenes, ((i)Pr(3)P)(2)(Cl)M=CHPh, which could not be prepared by other known methods, were synthesized by the sulfur ylide approach. The method is not limited to metal benzylidenes, as demonstrated by the preparation of the Ru vinyl-alkylidene, (PCy(3))(2)Cl(2)Ru=CH-CH=CH(2), methoxycarbonyl-alkylidene, (PCy(3))(2)Cl(2)Ru=CH(CO(2)Me), and alkylidene (PCy(3))(2)Cl(2)Ru=CH(CH(3)), (PCy(3))(2)Cl(2)Ru=CH(2) compounds. The problem of recycling of starting materials as well as the issue of facile purification of the product metal carbene complex were addressed by the synthesis of a polymer-supported diarylsulfide, the carrier of the carbenoid unit in the process. Based on the sulfur ylide route, a methodology for the synthesis of metallocarbenes anchored to a polymer via the carbene ligand, using a commercial Merrifield resin, was developed.