Metal-containing Product Research Articles

Mineral resources in life cycle impact assessment—defining the path forward

Despite 20 years of research, there remains no robust, globally agreed upon method—or even problem statement—for assessing mineral resource inputs in life cycle impact assessment (LCIA). As a result, inclusion of commonly used methods such as abiotic depletion potential (ADP) in life cycle assessment (LCA)-related evaluation schemes could lead to incorrect decisions being made in many applications. In this paper, we explore in detail how to improve the way that life cycle thinking is applied to the acquisition of mineral resources and their metal counterparts. This paper evaluates the current body of work in LCIA with regard to “depletion potential” of mineral resources. Viewpoints from which models are developed are described and analyzed. The assumptions, data sources, and calculations that underlie currently used methods are examined. A generic metal-containing product is analyzed to demonstrate the vulnerability of results to the denominator utilized in calculating ADP. The adherence to the concept of the area of protection (AOP) is evaluated for current models. The use of ore grades, prices, and economic availability in LCIA is reviewed. Results demonstrate that any work on resource depletion in a life cycle context needs to have a very clear objective or LCIA will not accurately characterize mineral resource use from any perspective and decision-making will continue to suffer. New, harmonized terminology is proposed so that LCA practitioners can build better mutual understanding with the mineral industry and recommendations regarding more promising tools for use in life cycle sustainability assessment (LCSA) are given. The economic issue of resource availability should be evaluated in parallel with traditional LCA, not within. LCIA developers should look to economists, the market, and society in general, for broader assessments that consider shorter-time horizons than the traditional LCIA methods. To do so, the concept of the AOP in LCA needs to be redefined for LCSA to ensure that models estimate what is intended. Finally, recommendations regarding mineral resource assessment are provided to ensure that future research has a sound basis and practitioners can incorporate the appropriate tools in their work.

Nitric Oxide Release from a Nickel Nitrosyl Complex Induced by One-Electron Oxidation

Reaction of [Ni(NO)(bipy)][PF6] (2) with AgPF6 or [NO][PF6] in MeCN results in formation of [Ni(bipy)x(MeCN)y](2+) and release of NO gas in moderate yields. In contrast, the addition of the inner sphere oxidant Ph2S2 to 2 does not result in denitrosylation. Instead, the diphenyldisulfide adduct [{(bipy)(NO)Ni}2(μ-S2Ph2)][PF6]2 (3) is formed in good yield. However, oxidation of 2 with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) does results in cleavage of the Ni-NO bond and generation of NO. The metal-containing product, [(bipy)Ni(η(2)-TEMPO)][PF6] (4), can be isolated as an orange-brown solid in excellent yields. In the solid state, complex 4 contains a side-on bound TEMPO(-) ligand, which is characterized by a long N-O bond length [1.383(2) Å]. The contrasting reactivity of Ph2S2 and TEMPO likely relates to their different redox potentials, as Ph2S2 is a relatively weak oxidant. Finally, the addition of pyridine-N-oxide to 2 results in the formation of the adduct, [(bipy)Ni(NO)(ONC5H5)][PF6] (5). No evidence of NO release is observed in this reaction, probably because of the low one-electron (1e(-)) reduction potential of pyridine-N-oxide.

Determination and Safety Assessment of Lead and Cadmium in Eye Shadows Purchased in Local Market in Tehran

Powdered eye shadows are the most used eye cosmetics in Iran. 120 samples of 15 brands of pressed powder eye shadows in main seven colors: pink, white, violet, brown, golden, green and blue made from different countries were randomly purchased for analysis but a single brand may contain several colors which have been analyzed. Data was collected on the cost, brand, and color of product and batch number of the products that was sampled. The samples were analyzed according to standardized international protocols by wet digestion method (Using HNO3, HClO4, H 2 O 2 ) analyzed by Atomic Absorption Spectrophotometer. Lead and cadmium detected in all colors in wide range of concentrations. The brown and golden colors in all brands have the highest concentrations of lead, while blue and green colors have the lowest Lead content and the golden and blue color have the highest and lowest concentration of cadmium respectively. Estimating the safety assessment of cosmetic products such as eye shadows is a complex issue. The concentration of cadmium shows significant differences of this heavy metal in the color main groups (p<0.005). This result reveals that the type of pigment used in eye shadows contributes to its heavy metal content. As toxic metals especially lead can rise to accumulate in body over time and repetitive metal-containing product application and probably lead to significant exposure levels, We recommended the major quality controls for the cosmetics products due to long contact with the skin of eyelids.

Oxygen Reduction Reactions of Monometallic Rhodium Hydride Complexes

Selective reduction of oxygen is mediated by a series of monometallic rhodium(III) hydride complexes. Oxidative addition of HCl to trans-Rh(I)Cl(L)(PEt(3))(2) (1a, L = CO; 1b, L = 2,6-dimethylphenylisocyanide (CNXy); 1c, L = 1-adamantylisocyanide (CNAd)) produces the corresponding Rh(III) hydride complex cis-trans-Rh(III)Cl(2)H(L)(PEt(3))(2) (2a-c). The measured equilibrium constants for the HCl-addition reactions show a pronounced dependence on the identity of the "L" ligand. The hydride complexes effect the reduction of O(2) to water in the presence of HCl, generating trans-Rh(III)Cl(3)(L)(PEt(3))(2) (3a-c) as the metal-containing product. In the case of 2a, smooth conversion to 3a proceeds without spectroscopic evidence for an intermediate species. For 2b/c, an aqua intermediate, cis-trans-[Rh(III)(OH(2))Cl(2)(L)(PEt(3))(2)]Cl (5b/c), forms along the pathway to producing 3b/c as the final products. The aqua complexes were independently prepared by treating peroxo complexes trans-Rh(III)Cl(L)(η(2)-O(2))(PEt(3))(2) (4b/c) with HCl to rapidly produce a mixture of 5b/c and 3b/c. The reactivity of the peroxo species demonstrates that they are plausible intermediates in the O(2)-reduction chemistry of hydride complexes 2a-c. These results together show that monometallic rhodium hydride complexes are capable of promoting selective reduction of oxygen to water and that this reaction may be controlled with systematic alteration of the ancillary ligand set.

Trianionic NCN3– Pincer Complexes of Chromium in Four Oxidation States (CrII, CrIII, CrIV, CrV): Determination of the Active Catalyst in Selective 1-Alkene to 2-Alkene Isomerization

The synthesis and characterization of a series of four Cr complexes in the +2, +3, +4, and +5 oxidation states supported by an NCN trianionic pincer ligand are reported. Treating CrMeCl2(THF)3 with the dilithio salt pincer ligand precursor {[2,6-iPrNCHN]Li2}2 provides the CrIII complex [2,6-iPrNCN]CrIII(THF)3 (1), CrIV complex [2,6-iPrNCN]CrIVMe(THF) (2), and CrII complex [2,6-iPrNHCN]CrII(THF)2 (3). Complexes 2 and 3 are the result of disproportionation. Treating 1 with 1 equiv of styrene oxide in THF converts the CrIII complex to the CrV(O) species [2,6-iPrNCN]CrV(O)(THF) (4). Complex 2, characterized by single-crystal X-ray diffraction, is a rare CrIV methyl complex that is kinetically stable at 25 °C; at 85 °C, Cr–Me bond homolysis occurs. The homolytic cleavage results in CH4 formation and biphenyl via a radical mechanism. The metal-containing product from thermolysis is the same CrII species formed during metalation, except one of the protons is substituted for a deuterium from C6D6 (3-d). Complex 2 is a precatalyst for the selective isomerization of 1-hexene and 1-octene to the corresponding 2-alkenes. An induction period occurs during the catalytic isomerization, and the active catalyst was determined to be the CrII complex 3, not 2.

Activation of Bis(guanidinate)lanthanide Alkyl and Aryl Complexes on Elemental Sulfur: Synthesis and Characterization of Bis(guanidinate)lanthanide Thiolates and Disulfides

The treatment of [(Me(3)Si)(2)NC(NCy)(2)](2)Ln(mu-Cl)(2)Li(THF)(2) with 1 equiv of BnK (Bn = benzyl) in toluene affords [(Me(3)Si)(2)NC(NCy)(2)](2)LnBn [Ln = Er (1-Er), Y (1-Y)] in good yields. Similarly, [(Me(3)Si)(2)NC(NCy)(2)](2)Ln(t)Bu [Ln = Er (2-Er), Yb (2-Yb)] are obtained in satisfactory yields by the reaction of [(Me(3)Si)(2)NC(NCy)(2)](2)Ln(mu-Cl)(2)Li(THF)(2) with (t)BuLi in hexane. 1 reacts with 1/8 equiv of S(8) in toluene to form the sulfur insertion products {[(Me(3)Si)(2)NC(NCy)(2)](2)Ln(mu-SBn)}(2) [Ln = Er (3-Er), Y (3-Y)], while the reaction of 2 with elemental sulfur under the same conditions affords the oxidation products {[(Me(3)Si)(2)NC(NCy)(2)](2)Ln}(2)(mu-eta(2):eta(2)-S(2)) [Ln = Er (4-Er), Yb (4-Yb)] regardless of the equivalency of S(8) employed. Disulfide complexes 4 can also be obtained by the reaction of 3 with (1)/(4) equiv of S(8). Furthermore, the treatment of [(Me(3)Si)(2)NC(NCy)(2)](2)Ln(mu-Cl)(2)Li(THF)(2) with 1 equiv of (n)BuLi in hexane, followed by reaction with (1)/(8) equiv of S(8), affords the dinuclear thiolate complexes {[(Me(3)Si)(2)NC(NCy)(2)](2)Ln(mu-S(n)Bu)}(2) [Ln = Y (5-Y), Er (5-Er)] in good yields. However, under the same conditions, [(Me(3)Si)(2)NC(NCy)(2)](2)Yb(mu-Cl)(2)Li(THF)(2) reacts with (n)BuLi and S(8) to give {[(Me(3)Si)(2)NC(NCy)(2)](2)Yb}(2)(mu-eta(2):eta(2)-S(2)) (4-Yb) as the main metal-containing product. [(Me(3)Si)(2)NC(NCy)(2)](2)LnPh (generated in situ from [(Me(3)Si)(2)NC(NCy)(2)](2)Ln(mu-Cl)(2)Li(THF)(2) and PhLi) also undergoes sulfur insertion, affording {[(Me(3)Si)(2)NC(NCy)(2)](2)Ln(mu-SPh)}(2) [Ln = Er (6-Er), Yb (6-Yb)] in good yields. All of the complexes were characterized by spectroscopic and elemental analyses. The structures of all of these compounds, except 3-Y, are also determined by single-crystal X-ray diffraction analysis. Surprisingly, 3, 5, and 6 bear the same space group and very similar cell parameters, despite the different thiolate ligands.

Alkyne insertion into cyclometallated pyrazole and imine complexes of iridium, rhodium and ruthenium; relevance to catalytic formation of carbo- and heterocycles

The cyclometallated complexes [MCl(C^N)(ring)] (HC^N = 2-phenylpyrazole, M = Ir, Rh ring = Cp*; M = Ru, ring = p-cymene) readily undergo insertion reactions with RC≡CR (R = CO(2)Me, Ph) to give mono insertion products, the rhodium complex also reacts with PhC≡CH regiospecifically to give an analogous product. The products of the reactions of the cyclometallated imine complexes [MCl(C^N)Cp*] (HC^N = PhCH=NR, R = Ph, CH(2)CH(2)OMe, Me; M = Ir, Rh) with PhC≡CPh depend on the substituent R; when R = CH(2)CH(2)OMe a monoinsertion is observed, however for R = Me the initial insertion product is unstable, undergoing reductive elimination with loss of the organic fragment, and for R = Ph no metal-containing product is isolated. With PhC≡CH the cyclometallated imine complexes can give mono or di-insertion products. The implications for catalytic synthesis of carbo- and heterocycles by a tandem C-H activation, alkyne insertion mechanism are discussed.

Measuring the metal-containing mass of pulp products using the electromagnetic method

Two ways of solving the problem of precisely measuring the metal-containing mass of pulp are considered. The first method involves continuously measuring the magnetic permeability of the pulp and automatically correcting the calculation of a dry mass of a metal-containing product. The second method involves applying the specific electromagnetic flowmeters insensitive to the variation in the magnetic properties of a measured medium. Technical solutions which allow one to obtain an additional electric signal characterizing the magnetic permeability of the pulp are analyzed. Its presence makes it possible not only to eliminate the error in measuring the volume flow rate due to the effect of the magnetic component of the pulp, but also to measure the mass of the metal-containing product. Applying the electromagnetic flowmeters is the most promising way to solve this problem.

Nitric Oxide‐Induced Fluorescence Enhancement by Displacement of Dansylated Ligands from Cobalt

The cobalt complexes [Co(Ds-AMP)(2)] (1) and [Co(Ds-AQ)(2)] (2), where Ds-AMP and Ds-AQ are the conjugate bases of dansyl aminomethylpyridine (Ds-HAMP) and dansyl aminoquinoline (Ds-HAQ), respectively, were synthesized in two steps as fluorescence-based nitric oxide (NO) sensors and characterized by X-ray crystallography. The fluorescence of the two complexes was significantly quenched in CH(3)CN or CH(3)OH compared to that of the free Ds-HAMP or Ds-HAQ ligands. Addition of NO to a CH(3)CN solution of 1 or 2 enhanced the integrated fluorescence emission by factors of 2.1(+/-0.3) or 3.6(+/-0.4) within 35 or 20 min, respectively. Introduction of NO to methanolic solutions of the complexes similarly increased the fluorescence by 1.4(+/-0.1) for 1 or 6.5(+/-1.4) for 2 within 1 h. These studies demonstrate that 1 and 2 can monitor the presence of NO with turn-on emission and that their fluorescence responses are more rapid than those of previously reported cobalt systems in coordinating solvents such as CH(3)CN and CH(3)OH. (1)H NMR and IR spectroscopic data revealed the formation of a [Co(NO)(2)](10) cobalt-dinitrosyl adduct, with concomitant dissociation of one ligand from the cobalt center, as the metal-containing product of the NO reactions, a result indicating NO-induced ligand release to be the cause of the fluorescence increase.

Photoinduced One-Electron Reduction of Alkyl Halides by Dirhodium(II,II) Tetraformamidinates and a Related Complex with Visible Light

Various substituted dirhodium tetraformamidinate complexes, Rh(2)(R-form)(4) (R = p-CF(3), p-Cl, p-OCH(3), m-OCH(3); form = N,N'-diphenylformamidinate), and the new complex Rh(2)(tpgu)(4) (tpgu = 1,2,3-triphenylguanidinate) have been investigated as potential agents for the photoremediation of saturated halogenated aliphatic compounds, RX (R = alkyl group). The synthesis and characterization of the complexes is reported, and the crystal structure of Rh(2)(tpgu)(4) is presented. The lowest energy transition of the complexes is observed at approximately 870 nm and the complexes react with alkyl chlorides and alkyl bromides under low energy irradiation (lambda(irr) > or = 795 nm), but not when kept in the dark. The metal-containing product of the photochemical reaction with RX (X = Cl, Br) is the corresponding mixed-valent Rh(2)(II,III)X (X = Cl, Br) complex, and the crystal structure of Rh(2)(p-OCH(3)-form)(4)Cl generated photochemically from the reaction of the corresponding Rh(2)(II,II) complex in CHCl(3) is presented. In addition, the product resulting from the dimerization of the alkyl fragment, R(2), is also formed during the reaction of each dirhodium complex with RX. A comparison of the dependence of the relative reaction rates on the reduction potentials of the alkyl halides and their C-X bond dissociation energies are consistent with an outer-sphere mechanism. In addition, the relative reaction rates of the metal complexes with CCl(4) decrease with the oxidation potential of the dirhodium compounds. The mechanism of the observed reactivity is discussed and compared to related systems.

Facile Transformations of Lanthanocene Alkyls to Lanthanocene Thiolate, Sulfide, and Disulfide Derivatives by Reaction with Elemental Sulfur

Treatment of [Cp2Ln(μ-Me)]2 with 2 equiv of elemental sulfur in toluene at room temperature leads to the formation of the methylthiolate complexes [Cp2Ln(μ-SMe)]2 [ Ln = Yb (1a), Y (1b), Er (1c), Dy (1d)] in good yields. While reaction of Cp2Y(nBu) with elemental sulfur in 1:1 stoichiometric ratio under the same conditions yields [(Cp2Y)2(μ3-S)(THF)]2 (2a) as the metal-containing product with the extrusion of nBuSnBu and nBuSSnBu, the corresponding insertion intermediate [Cp2Y(μ-SnBu)]2 (1e) could be isolated only by decreasing the relative amount of S8 under more mild reaction conditions. Furthermore, [Cp2Yb(μ-SEt)]2 reacts with 2 equiv of sulfur to give a mixture of [(Cp2Yb)2(μ3-S)(THF)]2 (2b) and [Cp2Yb(THF)]2(μ-η2:η2-S2) (3). 2b and 3 can also be prepared from the reaction of [Cp2Yb(μ-Me)]2 with excess elemental sulfur in THF. All these results demonstrate that lanthanocene thiolate complexes are unstable in solution with S8, and the nature of the alkyl ligands and reaction conditions has a great influence on the final product structures from the reaction of lanthanocene alkyls with elemental sulfur and provides an easy access to trivalent lanthanocene thiolate, sulfide, and disulfide complexes as well as thioethers and organic disulfides. Complexes 1−3 were characterized by elemental analysis and IR and mass spectroscopies. The structures of complexes 1a, 1e, 2a, 2b, and 3 are also determined through X-ray single-crystal diffraction analysis.

The unusual role of CO transfer in molybdenum-catalyzed asymmetric alkylations.

Spectroscopic and crystallographic studies were undertaken to gain insight into the mechanism of the highly regio- and enantioselective allylic aklylation reaction catalyzed by molybdenum. The chiral ligand (L*) consisting of the mixed benzamide/picolinamide of (S,S,)-trans-1,2-diaminocyclohexane reacts with a typical Mo precatalyst, (norbornadiene)Mo(CO)4, to give a neutral complex L*Mo(CO)4 in which the ligand binds to the metal in a bidentate fashion through the pyridine and adjacent amide group. Reaction of this complex with the methyl carbonate of cinnamyl alcohol gives the corresponding pi-allyl complex L*(CO)2Mo(eta3-CH2=CH-CHPh). NMR and X-ray crystallographic characterization of this complex reveal the ligand binds in a facially capping tridentate fashion via the pyridine nitrogen, the nitrogen of the adjacent amide group, which has now been deprotonated, and the carbonyl oxygen of the remote amide. Surprisingly, the face of the allyl group open to attack with nucleophiles is that which would lead to the sense of stereochemistry opposite to that which is observed in catalytic reactions. Furthermore, the allyl complex in its isolated form is unreactive toward sodium dimethyl malonate. However, in the presence of a source of carbon monoxide (either Mo(CO)6 or gaseous CO), the allyl complex reacts with malonate to give the typically observed branched alkylated product in high yield and enantiomeric excess. The metal-containing product of this reaction is the molybdate complex [L*Mo(CO)4]-Na+. Reaction of the molybdate complex with linear or branched allylic carbonates regenerates the allyl complex, thus closing the catalytic cycle. Both the allyl complex and the molybdate complex are the only metal-containing species observed by NMR in typical catalytic reactions and thus appear to be catalyst resting states. Turnover of the catalytic cycle therefore involves shuttling of carbon monoxide between the two catalyst resting states. Coordination of CO appears to be necessary to activate the allyl complex toward nucleophilic attack, in effect stabilizing the molybdenum fragment as a leaving group.

Evaluation of Enantiomerically Pure Binaphthol-Based Molybdenum Catalysts for Asymmetric Olefin Metathesis Reactions that Contain 3,3‘-Diphenyl- or 3,3‘-Dimesityl-Substituted Binaphtholate Ligands. Generation and Decomposition of Unsubstituted Molybdacyclobutane Complexes

Enantiomerically pure molybdenum imido alkylidene complexes were prepared that contain binaphtholate ligands substituted in the 3 and 3‘ positions with either phenyl (4; Mo(NAr)(CHCMe2Ph)[Ph](THF)) or 2,4,6-trimethylphenyl groups (5; Mo(NAr)(CHCMe2Ph)[Mes](THF); Ar = 2,6-i-Pr2C6H3). Compound 5 was found to be an anti trigonal bipyramidal complex in an X-ray study. Asymmetric metatheses employing complex 5 were found to proceed to high conversion and to give high product % ee, while reactions that employed complex 4 were found to give lower conversion and lower % ee. One ring-closing reaction with 5 was shown to take place at a rate that was proportional to catalyst and substrate. Molybdacyclobutane complexes were observed in solution during ring-closing reactions. The molybdacyclobutane complex generated by treating 5 with ethylene was found to be a trigonal bipyramidal species which decomposed to yield some propylene; the metal-containing product or products of decomposition could not be identified. Moly...

Coordination and Chemistry of Stable Cu(II) Complexes in the Gas Phase

A technique has been developed that provides a solution to the very considerable technical problem of preparing gas-phase complexes from transition metals in their higher oxidation states, i.e., Cu(II), Cr(III), Fe(II), etc. Charge transfer prevents complexes, such as [Cu·(H2O)n]2+, from being prepared via nucleation about an ion core, and yet these ions are pivotal to an understanding of transition metal chemistry. Discussed here are new results from a technique that appears capable of producing complexes from a wide variety of metals and ligands. Data are presented for copper(II) in association with 20 different ligands, including water, ammonia, pyridine, tetrahydrofuran, and benzene. For each [Cu·Ln]2+ system, two important quantities are identified: (i) the minimum number of ligands required to form a stable unit and (ii) the value of n for which the intensity distribution reaches a maximum. The data show considerable variation as a function of the composition and size of solvent molecule, with evidence of stable coordination shells containing between 2 and 8 molecules. In most instances, coordination shells containing more than four molecules can be attributed to the formation of an extended network of hydrogen bonds. Collisional activation of size-selected clusters reveals the presence of extensive ligand-to-metal electron transfer in the smaller complexes, and in several cases, charge transfer is also accompanied by chemical reactivity. The extent of charge transfer is frequently observed to be determined by the stability of the singly charged metal-containing product.

Oxo complexes of osmium(IV) formed via dioxygen activation. X-ray structures of [OsX(dcpe)2]PF6 (X = Cl, Br), [OsCl(eta 2-O2)(dcpe)2]BPh4, and [OsCl(O)(dcpe)2]BPh4 (dcpe = 1,2-bis(dicyclohexylphosphino)ethane).

Dioxygen addition to the 16-electron complexes [OsX(P-P)2]+ (3) gives the dioxygen adducts [OsCl(eta 2-O2)(P-P)2]+ (3), which in turn react with HCl gas to give the novel osmium(IV) oxo complexes trans-[OsX(O)(P-P)2]+ (5) (X = Cl, Br; P-P = 1,2-bis(dicyclohexylphosphino)ethane (dcpe), 1,2-bis(diethylphosphino)ethane (depe), 1,2-bis((2R,5R)-2,5-dimethylphospholano)benzene (Me-duphos)). The complexes [OsX(dcpe)2]+ (X = Cl, Br) (3) are studied by X-ray crystallography and are shown to have a "Y-shaped" coordination geometry in the equatorial plane. The X-ray structural analysis of [OsCl(eta 2-O2)(dcpe)2]+ (4a) reveals an exceptionally short O-O bond (1.315(5) A). trans-[OsCl(O)(dcpe)2]+ (5a), the first oxo complex of osmium(IV) investigated crystallographically, exhibits a long Os-O distance of 1.834(3) A. The reactivity of 4 and 5 as oxidants is described. The dioxygen complex 4a transfers one oxygen atom to PPh3 (to give Ph3PO) or oxidizes iodide ions to triiodide ions in the presence of anhydrous HCl. In both reactions, the corresponding oxo species 5a is quantitatively formed as the only metal-containing product. Oxo complexes 5 are surprisingly stable and unreactive toward standard reducing agents such as phosphines.

Kinetic and Thermodynamic Studies of Reaction of *Cr(CO)(3)C(5)Me(5), HCr(CO)(3)C(5)Me(5), and PhSCr(CO)(3)C(5)Me(5) with *NO. Reductive Elimination of Thermodynamically Unstable Molecules HNO and RSNO Driven by Formation of the Strong Cr-NO Bond.

Reaction of H-Cr(CO)(3)C(5)Me(5) with *NO at 1-2 atm pressure in toluene solution yields Cr(NO)(CO)(2)C(5)Me(5) as the sole metal-containing product in addition to N(2)O and HNO(2) as the principle nitrogen-containing products. N(2)O and HNO(2) are attributed to decomposition of the initial product HNO. Kinetic studies yield the rate law d[P]/dt = -k(2nd)( )(order)[HCr(CO)(3)C(5)Me(5)][*NO]; k(2nd)( )(order) = 0.14 M(-)(1) s(-)(1) at 10 degrees C, with DeltaH() = 11.7 +/- 1.5 kcal/mol and DeltaS() = -16.3 +/- 3.5 cal/(mol deg). The rate of reaction is not inhibited by CO. The kinetic isotope effect for reaction of D-Cr(CO)(3)C(5)Me(5) is k(H)/k(D) = 1.7. These observations are consistent with a first step involving direct H (D) atom transfer from the metal hydride to *NO, forming HNO. Also supporting this mechanism is the approximately 150-times slower reaction of H-Mo(CO)(3)C(5)Me(5) and failure to observe reaction for H-W(CO)(3)C(5)Me(5) in keeping with metal-hydrogen bond strengths Cr < Mo < W. Reaction of PhS-Cr(CO)(3)C(5)Me(5) with NO at 1-2 atm pressure in toluene solution also forms Cr(NO)(CO)(2)C(5)Me(5) as the sole metal-containing product. The initial product is the unstable nitrosothiol PhS-NO. Kinetic studies yield the rate law d[P]/dt = -k(1st)( )(order)[PhS-Cr(CO)(3)C(5)Me(5)]; k(1st)( )(order) = 3.1 +/- 0.3 x 10(-)(3) s(-)(1) at 10 degrees C, with DeltaH() = 21.6 +/- 1.2 kcal/mol, DeltaS() = + 3.9 +/- 1.5 cal/(mol deg). The rate of reaction is independent of both NO and CO pressure. The transition state in the first-order process is proposed to involve migration of bound thiolate to coordinated CO, forming Cr(CO)(2) (eta(2)-C(=O)SPh)C(5)Me(5). The enthalpy of reaction of *Cr(CO)(3)C(5)Me(5) and NO yielding Cr(NO)(CO)(2)C(5)Me(5) and CO has been measured by solution calorimetry: DeltaH degrees = -33.2 +/- 1.8 kcal/mol. The Cr-NO bond strength is estimated as approximately 70 kcal/mol and provides the net thermodynamic driving force for the proposed elimination of the unstable molecules HNO and PhSNO.

Molecular Routes to Metal Oxides and Metal Silicates. Synthesis and Thermal Decomposition Studies of Eclipsed Mo2[O2Si(OtBu)2]3 and W2(NHMe2)2[O2Si(OtBu)2]2[OSi(OH)(OtBu)2]2

Reaction of Mo2(NMe2)6 with 3 equiv of (tBuO)2Si(OH)2 afforded a new siloxide complex, Mo2[O2Si(OtBu)2]3 (1), as the only metal-containing product. An X-ray crystal structure determination reveals that 1 adopts an eclipsed structure with three di-tert-butoxysilanediolato ligands bridging the molybdenum centers in a symmetrical fashion. Lewis acidic complex 1 forms an isolable adduct with pyridine. Reaction of W2(NMe2)6 with 3 equiv of (tBuO)2Si(OH)2 afforded W2(NHMe2)2[O2Si(OtBu)2]2[OSi(OH)(OtBu)2]2 (3), which was isolated as air-sensitive orange crystals. In this molecule, two O2Si(OtBu)2 ligands bridge the W⋮W bond in an η1 ,η1 fashion, and OSi(OH)(OtBu)2 ligands are coordinated to each W atom. This molecule adopts a highly eclipsed conformation and has a 2-fold axis of symmetry which perpendicularly bisects the tungsten−tungsten bond. Complex 1 undergoes a two-step weight loss (by TGA), which corresponds to the initial loss of isobutene and water (at ca. 200 °C), followed by the loss of molybdenum by e...

A Study of Formation and Fragmentation of Ionic Complexes of α-Amino Acids and Peptides with Al(III)-Glycerol by Fast Atom Bombardment Mass Spectrometry

Complexation of aluminum ions {Al(III) in glycerol} with α-amino acids has been studied by FAB mass spectrometry. Twelve α-amino acids and cysteine methyl ester interact with different Al(III)-containing ions and form several cluster ions such as [M+117]+, [117={A1(III)+glycerol−2H}]; [M+231]+, [231={Al(III)+glycerol+ trifluoroacetic acid−2H}]; [M+233]+, [233={2Al(III)+2glycerol−5H}]; [2M+Al−2H]+ and [2M+117]+. Fragmentation of these adduct ions led to the formation of mainly metal-containing product ions. Fragmentation pathways were demonstrated with the help of the dissociation of Leu-d3, His-d4, Tyr-d4, Ser-d4, Cys-d4 and Cys methyl ester-d3 ion complexes in glycerol-d3. Aliphatic, aromatic and α-amino acids possessing functional side chains show differences in the fragmentation of [M+117]+ ions. Fourteen peptides of different chain lengths (two through six amino acids) also form adducts with Al(III)-glycerol. Dissociation of these complex ions, especially [M+Al−2H]+ ions provides information about side-chain functional groups and some sequence information. The site of the metal-ion interaction is mostly at the amide nitrogens.

Nickel complexes of 1,2-bis(diisopropylphosphino)ethane with sulfur-containing ligands

The complex [NiBr2(dippe)]1[dippe = 1,2-bis(diisopropylphosphino)ethane] reacted with benzene- and polyfluorobenzene-thiolates furnishing square-planar complexes [Ni(SR)2(dippe)](R = C6F52a, C6F4H 2b, C6H4F 2c or Ph 2d). These compounds reacted with CNBut and Na[BPh4] in EtOH to yield the derivatives cis-[Ni(SR)(CNBut)(dippe)][BPh4](R = C6F53a, C6F4H 3b, C6H4F 3c or Ph 3d). No reaction takes place with CO under similar conditions. These compounds exhibit fluxional behaviour in solution. Compound 1 also reacted with sodium dialkyldithiocarbamates affording [Ni(S2CNR2)(dippe)]Br (R = Et 4a or Me 4b), which contain one bidentate dithiocarbamate ligand. However, the reaction with alkyl dithiocarbonates occurs with degradation, and the ultimate metal-containing product is the dithiocarbonate complex [Ni(S2CO)(dippe)]5, the crystal structure of which has been determined. All the compounds have been characterized by IR and NMR spectroscopy and microanalysis.

ChemInform Abstract: SYNTHESIS OF 5‐AMINO‐4‐CYANOPYRAZOLE FROM 1,1‐DICYANOALKENES AND ELEMENTAL DINITROGEN USING A TUNGSTEN COMPLEX

AbstractDer aus Wolframhexachlorid zugängliche Komplex (VII) ergibt bei der elektrochemischen Reduktion das Amino‐cyano‐pyrazol (VIII).