Philippe Kalck

Carbon nanotubes and nanofibers in catalysis

This review analyses the literature from the early 1990s until the beginning of 2003 and covers the use of carbon nanotubes (CNT) and nanofibers as catalysts and catalysts supports. The article is composed of three sections, the first one explains why these materials can be suitable for these applications, the second describes the different preparation methods for supporting metallic catalysts on these supports, and the last one details the catalytic results obtained with nanotubes or nanofibers based catalysts. When possible, the results were compared to those obtained on classical carbonaceous supports and explanations are proposed to clarify the different behaviors observed.

Cobalt-Catalyzed Hydroformylation of Alkenes: Generation and Recycling of the Carbonyl Species, and Catalytic Cycle

In1938,whileOttoRoelenwasstudyingtheFischer-Tropsch reaction, which converts H2/CO into alkanes and alkenes, and was trying to improve the yields by recycling ethylene, the cobalt catalyst deposited on a ThO2/SiO2 support produced some propanal. Fortunately, Roelen focused on this unexpected reaction and discovered that cobalt was able to catalyze specifically the hydrocarbonylation of ethylene.1-3 It was rapidly established that this reaction, which has been extended to various alkenes, was occurring in the organic phase: homogeneous catalysis was born.

Parametric study for the growth of carbon nanotubes by catalytic chemical vapor deposition in a fluidized bed reactor

Multiwalled carbon nanotubes have been produced from H2–C2H4 mixtures on Fe–SiO2 catalysts by a fluidized bed catalytic chemical vapor deposition process. Various parameters such as the catalyst preparation, the residence time, the run duration, the temperature, the H2:C2H4 ratio, the amount of metal deposited on the support have been examined. The influence of these parameters on the deposited carbon yield is reported, together with observations of the produced material. This process allows an homogeneously distributed deposition of nanotubes (10–20 nm diameter), that remain anchored to the support.

Use of Water-Soluble Ligands in Homogeneous Catalysis

Publisher Summary This chapter deals with the preparation of water soluble ligands and their use in the synthesis of water-soluble complexes as well as in catalysis. An important advantage over heterogeneous systems is that selectivity is achieved by a modulation of the coordination sphere of the metal. However, a recurrent problem is the separation of the organic products from the active catalyst. Their performances are, however, diminished by losses of the metal in solution, thereby preventing any application in commercially viable processes. A more attractive approach has been made using water-soluble ligands that are poorly soluble in organic media, allowing the catalysis to be carried out in a two-phase system. Moreover, the method can be applied either by contacting the organic phase containing the parent complex with the sulfonated ligand dissolved in water, or by mixing the complex and the ligand of interest in a solvent in which both are soluble.

Structural diversity in coordination chemistry of tridentate and tetradentate polyphosphines of Group 6 to 10 transition metal complexes

Abstract Tridentate and tetradentate polyphosphines offer a huge variety of coordination modes to transition metals which lead, depending on the metal, to very different structural features in the resulting complexes. Steric effects being crucial in metal–phosphine complexes reactivity, a good knowledge of the molecular structures of the species is required both in the solid state and in solution. This article reviews from a structural point of view the monometallic and symmetrical homobimetallic complexes of the transition elements of Group 6 to 10 with tridentate and tetradentate phosphines. Concerning the classical triphosphines and tetraphosphines, emphasis was put on advances reported after the year 1994, since comprehensive reviews have covered the former period. Several anterior relevant results are, however, briefly mentioned when necessary. A second part is devoted to nitrogen- and sulfur-containing derivatives potentially tridentate and tetradentate ligands, and their coordination to the above-mentioned metals. The last part describes the complexes obtained with the less classical ferrocenyl polyphosphine ligands or their nitrogen-containing derivatives: each ligand having a potential tridentate or tetradentate coordination from either phosphorus or nitrogen donor atoms. The literature cutoff date was during the second half of 2000, but in a few cases, references to important work appearing during 2001 were made; however such coverage should be completed in a future compilation. An exhaustive quoting of catalytic applications and reaction chemistry was beyond the scope of this article mainly devoted to structural works. Nevertheless, in order to illustrate the importance of this chemistry, efforts were made to provide the reader with recent references that have marked the field, even in the absence of X-ray structural characterization.

Recent Advances in Amine Synthesis by Catalytic Hydroaminomethylation of Alkenes

Carbon–carbon coupling catalyzed by transition metals represents a powerful synthetic method to have an access to organic molecules, especially when they present a significant complexity. The strategy to transform abundant and not expensive reactants into products of pharmaceutical interest by the appropriate catalytic way is of fundamental interest, provided that high conversion rates and selectivities can be gained. During the past decade, considerable progress has been made to transform a simple alkene into an aldehyde by carbonylation, to condense it with an NH function‐containing molecule present in the medium, and to hydrogenate the resulting imine or enamine into the relevant amine. Rhodium complexes are able to catalyze this series of reactions and be an efficient synthetic tool to produce rather sophisticated amines in one‐pot reactions under mild conditions of pressure and temperature. In the future, the production of various amines required by the industry of fine chemicals looks attractive by means of this catalytic method.

Behaviour of water-soluble dinuclear rhodium complexes in the hydroformylation reaction of oct-1-ene

The biphasic hydroformylation reaction of oct-1-ene, has been investigated by using the water-soluble dinuclear complex [Rh2(μ-StBu)2(CO)2(TPPTS)2] as precursor. Addition of ethanol as a cosolvent dramatically improved the yields but the good regioselectivity in linear aldehyde observed for neat oct-1-ene—water systems (97%) decreased to 83% (for 22% ethanol w/w). It is shown that the dinuclear framework cannot be maintained, that the mononuclear complex [RhH(CO)(TPPTS)3] is formed, and that thiol and significant amounts of [Rh2(μ-StBu)2(CO)4] move into the organic phase. This reaction from the dinuclear species requires the simultaneous presence of water and carbon monoxide. Introduction of the water-soluble thiol HS(CH2)3NMe2 in the bridging positions affords the complex [Rh2(μ-S(CH 2)3NHMe2)2(CO)2(TPPTS)2]Cl2 which can be kept in the aqueous hase but has a low level of catalytic activity.

Cooperative effect between two metal centres in hydroformylation: Routes towards heterobimetallic catalysis

Abstract The Rh2(μ-SR)2(CO)2L2 complexes are good catalyst precursors for the hydroformylation reaction of alkenes under mild conditions; high conversion rates are obtained, but when L is a phosphite or triphenylphosphine ligand no more than 85% of linear aldehyde is obtained for a full selectivity of the conversion of alkenes into the corresponding aldehydes. Introduction of the water-soluble P(mSO3C6 H4)3 ligand leads to 96% of selectivity in linear aldehyde and solves the problem of catalyst recovery; in this case the CO/H2 or CO/H2O couples can be used as feedstock. Various bisphosphine L2 ligands can be introduced. These include several containing a transition metal centre (Zr, Fe, Ru). The major effect observed is electronic. Extension to heterobimetallic complexes was carried out. Various rhodium-palladium complexes have been synthesized and the first results of hydroformylation show that aldehydes are produced due to the presence of the rhodium centre.

A Facile Route to Carbonylhalogenometal Complexes (M = Rh, Ir, Ru, Pt) by Dimethylformamide Decarbonylation

Dimethyl formamide (DMF) can be a convenient source of the carbonyl ligand in the coordination chemistry of rhodium, ruthenium, iridium, and platinum. We have undertaken a thorough study concerning the course of this reaction. In a first step, DMF-containing complexes are produced, which is usually accompanied by chloride redistribution. Then, upon refluxing, carbonyl species in the same oxidation state are obtained, presumably as a result of HCl-mediated DMF decomposition. Provided that water levels are kept low, reduction can occur to provide the complexes [NH2(CH3)2][RhCl2(CO)2], [NH2(CH3)2][RuCl3(CO)2(DMF)], [RuCl2(CO)2(DMF)2], and [NH2(CH3)2][IrCl2(CO)2]. In the case of platinum, reduction is not effective and [NH2(CH3)2][PtCl3(CO)] is obtained. No carbonylpalladium species can be synthesized in this way, the reaction producing copious amounts of colloidal metal. Adding phosphanes to these chlorocarbonyl-containing solutions allows easy, one-step syntheses of a variety of complexes.

MOCVD of rhodium, palladium and platinum complexes on fluidized divided substrates: Novel process for one-step preparation of noble-metal catalysts

A new one-step method, entitled fluidized-bed metal-organic chemical vapor deposition (FBMOCVD) of preparing highly dispersed metal-supported catalysts is reported. The following complexes were studied and used as CVD precursors in presence of H2: [Rh(m-Cl)(CO)2]2, Rh(allyl)3, Rh(acac)(CO)2, Pd(allyl)(hfac), Pd(allyl)(Cp), Pt(COD)(CH3)2. (acac, acetylacetonato; hfac, hexafluoroacetylacetonato; Cp, cyclopentadienyl; COD, cyclooctadienyl). In a first approach, depositions on planar substrates were carried out to establish the best experimental conditions to obtain good-quality deposits. X-ray diffraction, X-ray photo-electron spectroscopy and electron microprobe studies were realized on the resulting thin films. Analyses of the products contained in the gas phase after and during deposition were performed by mass spectrometry and GC‐MS. Finally, catalysts prepared by FBMOCVD were characterized by transmission electron microscopy‐energy dispersion spectroscopy (TEM‐ EDS), metal-loading determinations and specific-surface measurements (BET). Dispersed nanosized aggregates were obtained, showing high activities in alkene hydrogenation and alcohol hydrocarbonylation. # 1998 John Wiley & Sons, Ltd.