Soluble Transition Metal Complexes Research Articles

Capturing the Role of Explicit Solvent in the Dimerization of RuV (bda) Water Oxidation Catalysts.

A ground-breaking empirical valence bond study for a soluble transition-metal complex is presented. The full reaction of catalyst monomers approaching and reacting in the RuV oxidation state were studied. Analysis of the solvation shell in the reactant and along the reaction coordinate revealed that the oxo itself is hydrophobic, which adds a significant driving force to form the dimer. The effect of the solvent on the reaction between the prereactive dimer and the product was small. The solvent seems to lower the barrier for the isoquinoline (isoq) complex while it is increased for pyridines. By comparing the reaction in the gas phase and solution, the proposed π-stacking interaction of the isoq ligands is found to be entirely driven by the water medium.

Robert Bergman wins Wolf Prize in Chemistry

For his discovery of the activation of carbon-hydrogen bonds of hydrocarbons by soluble transition-metal complexes, Robert Bergman has won the 2017 Wolf Prize in Chemistry. Bergman is the Gerald E.K. Branch Distinguished Professor of Chemistry at the University of California, Berkeley. The $100,000 prize is among five awards given out this year by the Israel-based Wolf Foundation to honor achievements in medicine, mathematics, physics, chemistry, and the arts. The awards are sometimes referred to as the Israeli Nobels. “I was both surprised and honored to hear about the Wolf Prize decision,” Bergman says. “I have immense respect for this program because it reflects the dedication of both the Wolf Foundation and the Israeli government to achievements in the arts and in fundamental, long-term research in science, even in the face of pressures that are increasing worldwide for short-term payoffs from research investments.” In the early 1980s, Bergman discovered the first

CH Bond Activation of Methane by a Transient η(2)-Cyclopropene/Metallabicyclobutane Complex of Niobium.

This study challenges the problem of the activation of a CH bond of methane by soluble transition metal complexes. High pressure solution NMR, isotopic labeling studies, and kinetic analyses of the degenerate exchange of methane in the methyl complex [Tp(Me2)NbCH3(c-C3H5)(MeCCMe)] (1) are reported. Stoichiometric methane activation by the mesitylene complex [Tp(Me2)Nb(CH2-3,5-C6H3Me2)(c-C3H5) (MeCCMe)] (2) giving 1 is also realized. Evidence is provided that these reactions proceed via an intramolecular abstraction of a β-H of the cyclopropyl group to form either methane or mesitylene from 1 or 2, respectively, yielding the transient unsaturated η(2)-cyclopropene/metallabicyclobutane intermediate [Tp(Me2)Nb(η(2)-c-C3H4) (MeCCMe)] A. This is followed by its mechanistic reverse 1,3-CH bond addition of methane yielding the product.

Synthesis Soluble Non-Ion Transition Metal Manganese(II), Cobalt(II), Nickel(II) Complexes of Diethylenetriamine-N,N′,N″-tri(acetyl-p-hydroxybenzoyl hydrazine)- N,N″- Bisacetic Acid as Potential Contrast Enhancement Agent

A novel ligand, diethylenetriamine-N,N′,N″-tri(acetyl-p-hydroxybenzoyl hydrazine)-N,N″-bisacetic acid, and its three soluble non-ion transition metal complexes, ML· nH2O (M = Mn, n = 4; M = Co, Ni, n = 2) have been synthesized and characterized on the basis of elemental analysis, molar conductivities, 1H NMR, FAB-MS, TG-DTA analysis, and IR methods. In addition, relaxivity of complexes are determined, The relaxivity (R1) of MnL, CoL, NiL, and Gd(DTPA)2– used as control are 6.33, 2.71, 2.60, and 4.34L·mmol−1·s−1, respectively. The spin-lattice relaxivity of MnL are larger than that of Gd(DTPA)2−. The results showed that complex of MnL may be a potential MRI contrast agent with high spin-lattice relaxivity, good solubility, low osmotic pressure due to non-ion complex.

Atom-economical reduction of carbon monoxide to methanol catalyzed by soluble transition metal complexes at low temperatures

Hydrocarbons and methanol are considered the preferred products of catalytic reduction of carbon monoxide derived from clean natural gas. In this paper, we focus on atom-economical synthesis of methanol catalyzed by soluble transition metal complexes as single-site catalyst precursors under mild reaction conditions. Of the metal systems reported in the literature, Ni complexes activated by alkoxide bases affected homogeneous CO reduction to methanol at low temperatures (80°–130 °C) and low pressures (2000–5000 kPa) to achieve CO conversion and methanol selectivity of >90 and >95, respectively. The involvement of mono- and multi- nuclear Ni species that readily interconvert under methanol producing conditions is invoked. A process based on such an active catalyst system would position methanol to be considered an inexpensive feedstock for the synthesis of other derivatives.

Mass, IR, electronic and EPR spectral studies on transition metal complexes with a new tetradentate 12-membered new macrocyclic ligand

Complexes of Cr(III), Co(II), Ni(II) and Cu(II) containing a novel macrocyclic tetradentate nitrogen donor (N 4) ligand prepared via reaction of 2,3-hexanedione and ethylenediamine has been prepared and characterized. The newly synthesized ligand (L) and its complexes have been characterized on the basis of elemental analysis, molar conductance, magnetic moment susceptibility, EI-Mass, IR, Electronic and EPR spectral studies. The complexes are of high-spin type and four coordinated tetrahedral, five coordinated square pyramidal and six coordinated octahedral/tetragonal geometries. The ligand (L) and its soluble transition metal complexes have also been screened against different bacteria and plant pathogenic fungi in vitro.

Synthesis of Primary Amines: First Homogeneously Catalyzed Reductive Amination with Ammonia.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of primary amines: first homogeneously catalyzed reductive amination with ammonia.

[reaction: see text] The synthesis of primary amines via reductive amination of the corresponding carbonyl compounds with aqueous ammonia is achieved for the first time with soluble transition metal complexes. Up to an 86% yield and a 97% selectivity for benzylamines were obtained in the case of various benzaldehydes by using a Rh-catalyst together with water-soluble phosphine and ammonium acetate. In the case of aliphatic aldehydes, a bimetallic catalyst based on Rh/Ir gave improved results.

ChemInform Abstract: Synthesis and Coordination Chemistry of Unsymmetrical Tetraazaporphyrins Containing Single Oxathia- and Thiacrown Substituents.

Abstract Singly crowned porphyrazines containing oxathia- and thiacrown ethers were prepared from a mixed condensation of 1,2-dicyanobenzene or its 3,4-dibutyl analog and the appropriate crowned maleonitrile precursor. Peripheral metal-binding to each porphyrazine was examined spectrophotometrically. The oxathiaether-crowned porphyrazines were found to coordinate Ag(I) and HgCl 2 , though all complexes suffered from poor solubility and complexes with the latter were unstable in polar media. With an interest in the formation of comparatively more stable and soluble heavy and transition metal complexes, two new sets of thiaether-crowned porphyrazines were examined. In these cases, coordination of Hg(II), Ag(I), Cu(I) and Cu(II) was observed with no evidence for complexation of Tl(I), Pb(II) or CdCl 2 .

Efficient catalytic isomerization of allylic alcohols to carbonyl compounds with water soluble rhodium complexes

Abstract The isomerization of allylic alcohols to carbonyl compounds catalysed by water soluble transition metal complexes of Rh, Ru and Pd in a water/n-heptane biphasic system is reported. The substrates investigated are secondary or primary alcohols bearing the C C bond in the terminal or inner position. Conversions into carbonyl compounds were quantitative except for geraniol (44 % yield in citronelal). Activities up to 2 500 h−1 and turnover numbers of more than 2 600 are reported. The differences in the observed reactivity within a family of C4–C8 homologous allylic alcohols is only related to thermodynamic parameters such as the solubility and L/L partition dictated by the hydrocarbon chain and not by their intrinsic reactivity. © 2000 Academie des sciences / Editions scientifiques et medicales Elsevier SAS

Synthesis and Coordination Chemistry of Unsymmetrical Tetraazaporphyrins Containing Single Oxathia- and Thiacrown Substituents

Singly crowned porphyrazines containing oxathia- and thiacrown ethers were prepared from a mixed condensation of 1,2-dicyanobenzene or its 3,4-dibutyl analog and the appropriate crowned maleonitrile precursor. Peripheral metal-binding to each porphyrazine was examined spectrophotometrically. The oxathiaether-crowned porphyrazines were found to coordinate Ag(I) and HgCl 2, though all complexes suffered from poor solubility and complexes with the latter were unstable in polar media. With an interest in the formation of comparatively more stable and soluble heavy and transition metal complexes, two new sets of thiaether-crowned porphyrazines were examined. In these cases, coordination of Hg(II), Ag(I), Cu(I) and Cu(II) was observed with no evidence for complexation of Tl(I), Pb(II) or CdCl 2.

Olefin polymerization and copolymerization with soluble transition-metal complex catalysts

Olefin polymerizations catalyzed by Cp'TiCl 2 (O-2,6- 1 Pr 2 C 6 H 8 ) (1-5; Cp' = cyclopentadienyl group), RuCl 2 (ethylene)(pybox) {7; pybox 2,6-bis[(4S)-4-isopropyl-2-oxazolin-2-yl]pyridine), and FeCl 2 (pybox) (8) were investigated in the presence of a cocatalyst. The Cp*TiC 2 (O-2,6- i Pr 2 C 6 H 3 ) (5)-methylaluminoxane (MAO) catalyst exhibited remarkable catalytic activity for both ethylene and 1-hexene polymerizations, and the effect of the substituents on the cyclopentadienyl group was an important factor for the catalytic activity. A high level of 1-hexene incorporation and a lower r E .r H value with 5 than with [Me 2 Si(C 5 Me 4 )(N t Bu)]TiCl 2 (6) were obtained, despite the rather wide bond angle of Cy-Ti-O (120.5°) of 5 compared with the bond angle of Cp-Ti-N of 6 (107.6°). The 7-MAO catalyst exhibited moderate catalytic activity for ethylene homopolymerization and ethylene/1-hexene copolymerization, and the resultant copolymer incorporated 1-hexene. The 8-MAO catalyst also exhibited activity for ethylene polymerization, and an attempted ethylene/1-hexene copolymerization gave linear polyethylene. The efficient polymerization of a norbornene macromonomer bearing a ring-opened poly(norbornene) substituent was accomplished by ring-opening metathesis polymerization with the well-defined MO(CHCMe 2 Ph)(N-2,6- i Pr 2 C 6 H 3 )[OCMe(CF 3 ) 2 ] 2 (10). The key step for the macromonomer synthesis was the exclusive end-capping of the ring-opened poly(norbornene) with p-Me 3 SiOC 6 H 4 CHO, and the use of 10 was effective for this polymerization proceeding with complete conversion.

Catalytic Carbon−Carbon Bond Activation of Unstrained Ketone by Soluble Transition-Metal Complex

Catalytic Carbon−Carbon Bond Activation of Unstrained Ketone by Soluble Transition-Metal Complex

Highly efficient heterogeneous polymer-supported Sharpless alkene epoxidation catalysts

More widespread, and cost effective, use of soluble transition metal complex asymmetric catalysts would be achieved if highly efficient heterogeneous analogues could be developed. We now report the synthesis of branched/crosslinked poly(tartrate ester)s and their use as heterogeneous ligands for the complexation of Ti(O iPr) 4, and use of the resulting insoluble catalysts in the asymmetric epoxidation of a range of trans-allylic alcohols employing t-butylhydroperoxide ( tBHP) as the oxidant. Isolated yields of epoxides of up to 80%, with enantiomeric excesses up to 98% have been achieved. Removal and recovery of the polymer catalyst is by simple filtration at the end of reactions. The influence of the ratio of polymer-ligand–titanium, and the polymer backbone molecular architecture on the activity and enantioselectivity of the catalysts has been assessed. Typically polymer branching ratios of 3–11% and a polymer-ligand:titanium ratio of 2:1 yield the optimum results.

有機合成化学の挑戦‐２１世紀に向けて 合成反応 Ｃ‐ＨおよびＣ‐Ｃ結合の合成化学的変換への挑戦

Breaking of inert chemical bonds by transition metals under homogeneous conditions has recently made rapid progress. In this review is described an overview of this field, especially the feature related to organic synthesis. The first part deals with breaking of carbon-hydrogen bonds. Ruthenium complexes catalyze the direct addition of ortho carbon-hydrogen bonds in aromatic ketones to olefins with high efficiencies and selectivities. A variety of analogous synthetic reactions involving breaking of Csp2-H bonds have been developed. The latter part features a recent aspect on the activation of C-C bonds through a process of oxidative addition to a soluble transition metal complex. Selective breaking of the C-C bonds α to the carbonyl group of cyclobutanones is achieved by a rhodium (I) complex.

Transition Metal Complexes with Sulfur Ligands, Part 119. Synthesis of Water Soluble Fe and Ru Complexes with Novel Multidentate Thioether Thiolate Ligands Containing Carboxylate Substituents

AbstractIn search of water soluble transition metal complexes with sulfur dominated coordination spheres that model key reactions of nitrogenases, the benzenedithiol derivatives ‘CO2HS2’‐H2 (1) and ‘CO2Me‐S2’‐H2 (2) were synthesized as precursors for multidentate sulfur ligands. The template alkylation of 2 by C2H4Br2 at [Fe(CO)2] fragments yielded a mixture of two diastereomeric C2 symmetrical [Fe(CO)2(‘CO2Me‐S4’)] complexes (4a and 4b), which were separated by crystallization. The hydrolysis of the mixture of the diastereomers 4a and 4b led to the isomerically pure tetradentate thioether thiol ligand ‘CO2Me‐S4’‐H2 (5) proving the regioselectivity of the template alkylation of the asymmetrical dithiol 2. The C1 symmetrical [Fe(‘CO2Me‐S2’)2]2‐ anion is an intermediate of the template alkylation and was isolated as (AsPh4)2 [Fe(‘CO2Me‐S2’2] (11), 4a, 5 and 11 were characterized by X‐ray structural analysis. Saponification of the methyl ester groups of 5 yielded ‘CO2H‐S4’‐H2 (7). Treatment of 7 with FeCl2 · 4 H2O in the presence of CO and LiOMe gave a mixture of two C2 symmetrical and water soluble diastereomers of Li2[Fe(CO)2(‘CO2‐S4’)] (8). Upon treatment with [RuCl2 (PPh3)3] 7 yielded isomerically pure [Ru(PPh3)2‐(‘CO2H‐S4’)] (9). 9 also exhibits C2 symmetry and could be reversibly deprotonated to form the water soluble complex K2[Ru(PPh3)2 (‘CO2‐S4’)] (10). Treatment of (NBu4)2 (‘CO2MeS2’) with “Ru(NO)Cl3” led to isomerically pure (NBu4)[Ru(NO)(‘CO2Me‐S2’)2] (12).

Breaking of the C−C Bond of Cyclobutanones by Rhodium(I) and Its Extension to Catalytic Synthetic Reactions

A study of rhodium(I)-catalyzed synthetic transformations involving selective breaking of the C−C bond α to the carbonyl group of cyclobutanones is described. Decarbonylation took place on treatment of a cyclobutanone with an equimolar amount of (Ph3P)3RhCl at reflux in toluene to afford the corresponding cyclopropane. The formation of the cyclopropane suggests that Rh(I) undergoes an insertion into the bond between the carbonyl carbon and the α-carbon in the initial step. Catalytic decarbonylation of cyclobutanone was also achieved. The mode and rate of the reaction depended greatly on the ligands of the rhodium(I) complex. When a cyclobutanone bearing a hydrogen atom at the 3-position was used, appropriate choice of the catalyst system led to the selective formation of either a cyclopropane or an alkene. Breaking of the carbon−carbon bond was next combined with hydrogenolysis. When cyclobutanone was treated under hydrogen pressure with a catalytic amount of a rhodium(I) complex having a bidentate diphosphine ligand like 1,2-bis(diphenylphosphino)ethane, a ring-opened alcohol was produced in good yield. Selective breaking of C−C bonds by a soluble transition metal complex is achieved in these practical synthetic processes.

Selective activation of carbon–carbon bonds next to a carbonyl group

ORGANOMETALLIC complexes are used to effect a wide range of catalytic transformations in organic synthesis, such as the activation of C–H bonds1,2. Carbon–carbon bonds, however, are generally unreactive towards transition metals under homogeneous conditions. C–C bond activation by a process of oxidative addition to soluble transition-metal complexes has been limited mostly to stoichiometric (not catalytic) reactions1,3–7,18, to highly strained substrates such as cyclopropane and cubane1,8–11or to chelating ketones19. Here we present a synthetically useful process of selective C–C bond activation in which the C–C bond adjacent to a carbonyl group is opened by insertion of a soluble rhodium(I) complex. The resulting organometallic intermediate can be transformed to a variety of products in a way that regenerates the rhodium complex. We anticipate that this catalytic scheme will have considerable utility in organic synthesis.

Catalytic Activation of Carbon-Fluorine Bonds by a Soluble Transition Metal Complex

Homogeneous catalytic activation of the strong carbon-fluorine bonds under mild conditions was achieved with the use of rhodium complexes as catalysts. The catalytic reactions between polyfluorobenzenes and hydrosilanes result in substitution of fluorine atoms by hydrogen atoms and are chemo- and regioselective. With individual stoichiometric steps observed and combined, and with intermediates isolated and fully characterized (including crystal structures), these systems demonstrate the effectiveness of a rational approach to catalytic design.

Book Review: Homogeneous Catalysis. The Applications and Chemistry of Catalysis by Soluble Transition Metal Complex, By G. W. Parshall and S. D. Ittel

Book Review: Homogeneous Catalysis. The Applications and Chemistry of Catalysis by Soluble Transition Metal Complex, By G. W. Parshall and S. D. Ittel