[Cp*Cr(C₆F₅)(Me)(Py)] as a Living Chromium(III) Catalyst for the “Aufbaureaktion”

The reaction of [Cp*Cr(C6F5)(μ-Cl)]2 (1) with 2 equiv of MeLi in THF yields the methyl-bridged Cr(III) dimer [Cp*Cr(C6F5)(μ-Me)]2 (2). This dinuclear compound is very soluble in hydrocarbon solvent and has been isolated in low yield (6%). Compound 2 reacts with pyridine to afford [Cp*Cr(C6F5)(Me)(Py)] (3), which has been isolated in a 67% yield. Compound 3 is a 15-electron, coordinatively saturated chromium(III) species that has been characterized by NMR, magnetometry, and EA. The structures of 1, 2, and 3 have been determined by single-crystal X-ray diffraction. Compounds 1 and 2 exist in the form of centrosymmetrical dimers with bridging chloride and methyl ligands, respectively. Mononuclear compound 3 adopts the expected three-legged piano stool geometry. Compound 2 polymerizes ethylene in toluene under 1 atm of ethylene at room temperature in the absence of any activators. Compound 3 is not catalytically active by itself. Yet, the addition of excess AlEt3 to a solution of 3 in toluene leads to a catalytic system that readily oligomerizes ethylene. Oligomerization experiments carried out with [3] = 10-3 M and [AlEt3] = 4.5 × 10-2 M for 15 min lead to the production of ethylene oligomers with an activity of 221 kg mol Cr-1 h-1. As indicated by gas chromatography, the Poisson distribution formula accounts for the molecular weight distribution of the growing ethylene oligomers during this reaction, which is indicative of a living polymerization system. Experiments carried out at higher AlEt3 concentrations ([3] = 10-3 M and [AlEt3] = 9 × 10-2 M) lead to a lower activity (150 kg mol Cr-1 h-1) but still present the characteristic features of a living polymerization system. These results are interpreted on the basis of a catalytic cycle in which the chain grows at chromium and is transferred to aluminum via an alkyl-bridged chromium−aluminum bimetallic intermediate

[Cp*Cr(C₆F₅)(Me)(Py)] as a Living Chromium(III) Catalyst for the “Aufbaureaktion”

The reaction of [Cp*Cr(C6F5)(μ-Cl)]2 (1) with 2 equiv of MeLi in THF yields the methyl-bridged Cr(III) dimer [Cp*Cr(C6F5)(μ-Me)]2 (2). This dinuclear compound is very soluble in hydrocarbon solvent and has been isolated in low yield (6%). Compound 2 reacts with pyridine to afford [Cp*Cr(C6F5)(Me)(Py)] (3), which has been isolated in a 67% yield. Compound 3 is a 15-electron, coordinatively saturated chromium(III) species that has been characterized by NMR, magnetometry, and EA. The structures of 1, 2, and 3 have been determined by single-crystal X-ray diffraction. Compounds 1 and 2 exist in the form of centrosymmetrical dimers with bridging chloride and methyl ligands, respectively. Mononuclear compound 3 adopts the expected three-legged piano stool geometry. Compound 2 polymerizes ethylene in toluene under 1 atm of ethylene at room temperature in the absence of any activators. Compound 3 is not catalytically active by itself. Yet, the addition of excess AlEt3 to a solution of 3 in toluene leads to a catalytic system that readily oligomerizes ethylene. Oligomerization experiments carried out with [3] = 10-3 M and [AlEt3] = 4.5 × 10-2 M for 15 min lead to the production of ethylene oligomers with an activity of 221 kg mol Cr-1 h-1. As indicated by gas chromatography, the Poisson distribution formula accounts for the molecular weight distribution of the growing ethylene oligomers during this reaction, which is indicative of a living polymerization system. Experiments carried out at higher AlEt3 concentrations ([3] = 10-3 M and [AlEt3] = 9 × 10-2 M) lead to a lower activity (150 kg mol Cr-1 h-1) but still present the characteristic features of a living polymerization system. These results are interpreted on the basis of a catalytic cycle in which the chain grows at chromium and is transferred to aluminum via an alkyl-bridged chromium−aluminum bimetallic intermediate

Monodisperse Thioether-Stabilized Palladium Nanoparticles: Synthesis, Characterization, and Reactivity

Size control of monodisperse palladium nanoparticles with sizes ranging from 1.7 to 3.5 nm was accomplished using thioethers as stabilizing ligands, in a one-step procedure. Modulation of the reaction temperature, reaction time, solvent, and carbon chain length of the thioether provided control over the nanoparticle size and size distribution. The resulting Pd nanoparticles were characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD). 1H NMR spectroscopy provided insight into the thioether−Pd nanoparticle surface interaction. To demonstrate the catalytic activity of the thioether-stabilized Pd nanoparticles, hydrogenation reactions were carried out using the as-synthesized Pd nanoparticles. We observed a trend in the reactivity of the nanoparticles with respect to their size, however, recovery of the nanoparticles following subsequent reactions was rather challenging. Immobilization of the Pd nanoparticles onto commercial SiO2 resulted in rapid and efficient catalysis, successful recovery of the Pd nanoparticles, and furthermore, the nanoparticles could be used up to 8 times with no measurable decrease in catalytic activity. This work demonstrates the utility of thioether ligands for the synthesis of monodisperse Pd nanoparticles that are efficient catalysts for various organic transformations

A Novel Example of the Reductive Cyclization of a Diyne at a Re−Re Triple Bond: The Reaction of Re₂Cl₄(μ-dppm)₂ with 1,7-Octadiyne

The triply bonded dirhenium(II) complex Re2Cl4(μ-dppm)2 (1; dppm = Ph2PCH2PPh2) reacts with 1,7-octadiyne to produce the novel dirhenium(III) complex Re2Cl3(μ,η2-C8H7)(μ-dppm)2 (2). The dirhenium complex 1 serves both as a reagent for the 2-electron reductive cyclization of the diyne and as the template to stabilize the resulting [C8H7Re2] bridging unit, which is of a type not previously encountered in multiple bond dimetal chemistry

Effect of the Alkali-Metal Cation on the Bonding Mode of 2,5-Dimethylpyrrole in Divalent Samarium and Ytterbium Complexes

The reactions of SmI2(THF)2 and YbI2(THF)2 with the alkali-metal salts of 2,5-dimethylpyrrole, or the reaction of SmCl3(THF)3 and YbCl3(THF)3 with the same ligands followed by reduction with the appropriate alkali metals, led to the formation of divalent mono- and polynuclear complexes. Structural analysis of these complexes indicated that the bonding mode adopted by the ligand depends on the nature of the alkali-metal cation retained in the structure

Complexation of the Triply-Bonded Dirhenium(II) Complex Re₂Cl₄(μ-dppm)₂ (dppm = Ph₂PCH₂PPh₂) by Up to Three Acetylene Molecules

The triply bonded dirhenium(II) synthons Re2X4(μ-dppm)2 (X = Cl, Br; dppm = Ph2PCH2PPh2) react with acetylene at room temperature in CH2Cl2 and acetone to afford the bis(acetylene) complexes Re2X4(μ-dppm)2(μ:η2,η2-HCCH)(η2-HCCH) (X = Cl (3), Br(4)). Compound 3 has been derivatized by reaction with RNC ligands in the presence of TlPF6 to give unsymmetrical complexes of the type [Re2Cl3(μ-dppm)2(μ:η2,η2-HCCH)(η2-HCCH)(CNR)]PF6 (R = Xyl (5), Mes (6), t-Bu (7)), in which the RCN ligand has displaced the chloride ligand cis to the η2-HCCH ligand. The reaction of 3 with an additional 1 equiv of acetylene in the presence of TlPF6 gives the symmetrical all-cis isomer of [Re2Cl3(μ-dppm)2(μ:η2,η2-HCCH)(η2-HCCH)2]PF6 (8). The two terminal η2-HCCH ligands in 8 are very labile and can be displaced by CO and XylNC to give the complexes [Re2Cl3(μ-dppm)2(μ:η2,η2-HCCH)(L)2]Y (L = CO when Y = PF6 (9); L = CO when Y = (PF6)0.5/(H2PO4)0.5 (10); L = XylNC when Y = PF6 (11)). These substitution reactions proceed with retention of the all-cis stereochemistry. Single-crystal X-ray structure determinations have been carried out on complexes 3, 5, 8, 10, and 11. In no instance have we found that the acetylene ligands undergo reductive coupling reactions

Effect of the Alkali-Metal Cation on the Bonding Mode of 2,5-Dimethylpyrrole in Divalent Samarium and Ytterbium Complexes

The reactions of SmI2(THF)2 and YbI2(THF)2 with the alkali-metal salts of 2,5-dimethylpyrrole, or the reaction of SmCl3(THF)3 and YbCl3(THF)3 with the same ligands followed by reduction with the appropriate alkali metals, led to the formation of divalent mono- and polynuclear complexes. Structural analysis of these complexes indicated that the bonding mode adopted by the ligand depends on the nature of the alkali-metal cation retained in the structure

Effect of the Alkali-Metal Cation on the Bonding Mode of 2,5-Dimethylpyrrole in Divalent Samarium and Ytterbium Complexes

The reactions of SmI2(THF)2 and YbI2(THF)2 with the alkali-metal salts of 2,5-dimethylpyrrole, or the reaction of SmCl3(THF)3 and YbCl3(THF)3 with the same ligands followed by reduction with the appropriate alkali metals, led to the formation of divalent mono- and polynuclear complexes. Structural analysis of these complexes indicated that the bonding mode adopted by the ligand depends on the nature of the alkali-metal cation retained in the structure

Isolation and Characterization of Linear Polymeric {[1,1-H₁₀C₆(α-C₄H₃N)₂]₂Sm[Na(THF)]₂}<i>_n</i>: A 30-Electron Species with a (η⁵-Cp)₄Ln Type Structure

Reduction of the tetranuclear dinitrogen cluster {[1,1-H10C6(α-C4H3N)2]Sm}4(THF)2(μ-N2) with Na sand in THF afforded the linear polymeric divalent Sm complex {[1,1-H10C6(α-C4H3N)2]2Sm[Na(THF)]2}n, where each samarium atom is surrounded by four η5-bonded pyrrolide rings, thus giving the metal center a formal 30-electron configuration

Effect of the Alkali-Metal Cation on the Bonding Mode of 2,5-Dimethylpyrrole in Divalent Samarium and Ytterbium Complexes

The reactions of SmI2(THF)2 and YbI2(THF)2 with the alkali-metal salts of 2,5-dimethylpyrrole, or the reaction of SmCl3(THF)3 and YbCl3(THF)3 with the same ligands followed by reduction with the appropriate alkali metals, led to the formation of divalent mono- and polynuclear complexes. Structural analysis of these complexes indicated that the bonding mode adopted by the ligand depends on the nature of the alkali-metal cation retained in the structure