Rapid, selective, and high-yield hydrogenation of CO2 can be achieved if the CO2 is in the supercritical state (scCO2). Dissolving H2, a tertiary amine, a catalyst precursor such as RuH2[P(CH3)3]4 or RuCl2[P(CH3)3]4, and a promoting additive such as water, CH3OH, or DMSO in scCO2 at 50 °C leads to the generation of formic acid with turnover frequencies up to or exceeding 4000 h-1. In general, experiments in which a second phase was formed by one or more reagents or additives had lower rates of reaction. The high rate of reaction is attributed to rapid diffusion, weak catalyst solvation, and the high miscibility of H2 in scCO2. The formic acid synthesis can be coupled with subsequent reactions of formic acid, for example, with alcohols or primary or secondary amines, to give highly efficient routes to formate esters or formamides. With NH(CH3)2, for example 420 000 mol of dimethylformamide/mol of Ru catalyst was obtained at 100 °C. The demonstrated solubility and catalytic activity of complexes of tertiary...

Homogeneous catalysis in supercritical fluids : hydrogenation of supercritical carbon dioxide to formic acid, alkyl formates, and formamides

https://www.chem.ccu.edu.tw/~joyce/referance/ericyang/Organometallics/Organometallics%201998,%2017,%205801-5809.pdf

N-Heterocyclic Carbene, Silylene, and Germylene Complexes of MCl (M = Cu, Ag, Au). A Theoretical Study1

The known complex {Cp(PPh3)2Ru}2(μ-C⋮CC⋮C) (3-Ph) and its PMe3-substitution product {Cp(PPh3)(PMe3)Ru}2(μ-C⋮CC⋮C) (3-Me) have been shown by cyclic voltammetry to undergo a series of four stepwise one-electron oxidation processes. Successive oxidation potentials (V) for the first three reversible processes of 3-Ph (3-Me) are −0.23 (−0.26), +0.41 (+0.33), and +1.03 (+0.97); the fourth, irreversible oxidation at +1.68 (+1.46) V is accompanied by chemical transformation followed by further oxidation. Chemical oxidation of 3-Ph with 1 or 2.5 equiv of AgPF6 in CH2Cl2/1,2-dimethoxyethane gave the one- and two-electron oxidized species [3-Ph][PF6] and [3-Ph][PF6]2, respectively. The chemical and electrochemical studies have been complemented by a series of detailed spectroelectrochemical experiments to obtain spectral data associated with the 3n+ (n = 0−4) species from 1500 to 40 000 cm-1, without necessitating the isolation of each individual species. Theoretical techniques have been employed in order to probe t...

Oxidation chemistry of metal-bonded C4 chains: A combined chemical, spectroelectrochemical, and computational study

Ruthenium and osmium carbene compounds that are stable in the presence of a variety of functional groups and can be used to catalyze olefin metathesis reactions on unstrained cyclic and acyclic olefins are disclosed. Also disclosed are methods of making the carbene compounds. The carbene compounds are of the formula 
where M is Os or Ru; R 1 is hydrogen; R is selected from the group consisting of hydrogen, substituted or unsubstituted alkyl, and substituted or unsubstituted aryl; X and X 1 are independently selected from any anionic ligand; and L and L 1 are independently selected from any neutral electron donor. The ruthenium and osmium carbene compounds of the present invention may be synthesized using diazo compounds, by neutral electron donor ligand exchange, by cross metathesis, using acetylene, using cumulated olefins, and in a one-pot method using diazo compounds and neutral electron donors. The ruthenium and osmium carbene compounds of the present invention may be used to catalyze olefin metathesis reactions including, but not limited to, ROMP, RCM, depolymerization of unsaturated polymers, synthesis of telechelic polymers, and olefin synthesis.

High metathesis activity ruthenium and osmium metal carbene complexes

An extensive survey of the occurrences and origins of both structural trans-effects (STEs) and kinetic trans-effects (KTEs) in octahedral d-transition metal complexes is presented. This allows the identification of general STE classes into which the majority of common ligands fit: (a) very large STE ligands (STE vs. Cl − >ca. 0.20 A): SiR 3 − , NO − , N 3− , O 2− , S 2− , RC 3− ; (b) large STE ligands (ca. 0.20>STE vs. Cl − >ca. 0.10 A): H − , R − , η 1 -alkenyl, η 1 -Ph, RCO − , RN 2 − ; (c) moderate STE ligands (ca. 0.10 A>STE vs. Cl − >0.00 A): CO, CN − , CNR, η 1 -acetylide, R 2 C, NO 2 − , NS + , RN 2 + , SO 3 2− , RSO 2 − , PR 3 , P(OR) 3 , RNH − , RS − , η 1 -thiones. The NO + ligand best illustrates the mutual nature of STEs, since it shows moderate STEs when trans to π-acceptor ligands, negligible STEs when trans to purely σ-donor ligands, and inverse STEs when trans to π-donors. STEs can sometimes show a marked dependency upon the electronic properties of the complexed metal centre, e.g. π-accepting RNC and PR 3 ligands generally give moderate STEs, but in d 0 complexes their STEs are weaker than that of Cl − . This may be attributed to an absence of π-back-bonding in such complexes. Also, the STEs of π-donating RN 2– ligands show an extremely wide variation which partially correlates with the metal d-configuration. The relationship between STEs and KTEs depends upon ligand substitution mechanisms, and because such reactions in octahedral complexes are generally dissociatively activated, there is often a close correlation between STEs and KTEs. For example, N 3− causes very large STEs and KTEs, whilst SO 3 2− gives moderate STEs and large KTEs. Since both of these ligands cause STEs primarily via powerful electron donation, the ground state destabilisations implied by STEs are likely to be accompanied by stabilisation of the electron-deficient five-co-ordinate transition states. By contrast, π-acceptor ligands such as CO or RNC generally exert moderate STEs, but cause pronounced delabilisation of trans metalligand bonds due to destabilisation of transition states.

Trans-Effects in Octahedral Transition Metal Complexes

A mononuclear, low-valent, electron-rich osmium methylene complex

This paper describes the synthesis of trinuclear metal complexes containing benzene in a new face-capping bonding mode, (μ 3 :η 2 :η 2 :η 2 -C 6 H 6 ), that accurately models the coordination geometry of benzene chemisorbed non surface of a close-packed metal lattice. [Os 3 (CO) 9 (μ 3 :η 2 :η 2 :η 2 -C 6 H 6 )]

A face-capping bonding mode for benzene in triosmium carbonyl cluster complexes

Octahedral carbyneosmium(II) complexes

Sulfene-transition metal complexes from SO2 addition to terminal methylene complexes of osmium(0) and iridium(I). Structure of )Cl(NO)(PPh3)2

A terminal methylene complex of iridium(I), Ir(=CH2)I(CO)(PPh3)2, and rearrangement to an ortho-metallated phosphorus ylide complex, Ir(CH2PPh2C6H4)HI(CO)(PPh3)

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