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International audience; New titanium complexes of general formula [Ti(OR)2(OiPr)2], containing functionalized alkoxido ligands, were developed for the selective catalytic dimerization of ethylene to 1-butene using a combined High Throughput Screening (HTS) / Design of Experiment (DoE) approach. First, a library of 19 ligands was elaborated and a primary screening spotted the phosphorus-functionalized alkoxido ligands as most promising. A second, more focused library containing 8 alkoxidophosphane ligands was then developed. A longer linear spacer between the alkoxido and the phosphorus functions, as in [Ti(19)2(OiPr)2], was found beneficial for this catalytic reaction. After identification of the best co-catalyst (AlEt3) and co-ligand (OnBu), final optimization of the reaction conditions was performed using a design of experiments (DoE) approach. The complex [Ti(19)2(OnBu)2] was shown to selectively dimerize ethylene in 1-butene (C4(α)=93 % (99+%)) at 30 bar C2H4 and 55 °C with AlEt3 as co-catalyst, resulting in very high activity and selectivity for a molecular titanium catalyst (13000 g gTi−1 h−1, 93 % 1-butene).

International audience; The transformation of ethylene and alkenes is of high importance for the chemical industry. In this review, we focus on selective alkenes transformation where metallacyclopentane is suspected or demonstrated to be involved in the reaction mechanism. In addition to the alkenes, the "classical" products of ethylene oligomerization, we also cover articles dealing with the synthesis of cyclobutane and butadiene derivatives, through the common metallacycle intermediate. We also present studies that help decipher the precise mechanism of the transformations, i.e. involving synthesis of postulated intermediates, labelling experiments and DFT calculations.

International audience; A family of L2Ni(ORF)2 (L2: (Cy3PO)24, dcpmS 5, dppf 9, bipyMe210; RF = C(CF3)3) complexes is synthesized via selective substitution of 2 equiv of (DME)NaORF from homoleptic [Ni(ORF)4][Na(DME)]2 complex 1, all characterized by 19F and 1H NMR and SCXRD analyses as well as elemental analyses. These L2Ni(ORF)2 precursors, activated by 2 equiv of PhF → Al(ORF)3, were active in ethylene oligomerization with selectivity toward butenes up to 97% and activities ranging from 10 to 50 kgC2H4·gNi·h–1. Mechanistic investigations, involving experiments with C2H4/C2D4 (1/1) coupled with GC-MS analysis, revealed the formation of a Ni–H fragment in the catalytic process. The L2Ni(ORF)2/2PhF → Al(ORF)3 catalytic system thus dimerizes ethylene through a Cossee–Arlman mechanism.

International audience; Upon reaction with copper(i), peri-halo naphthyl phosphines readily form peri-bridged naphthyl phosphonium salts. The reaction works with alkyl, aryl and amino substituents at phosphorus, with iodine, bromine and chlorine as a halogen. It proceeds under mild conditions and is quantitative, despite the strain associated with the resulting 4-membered ring structure and the naphthalene framework. The transformation is amenable to catalysis. Under optimized conditions, the peri-iodo naphthyl phosphine 1-I is converted into the corresponding peri-bridged naphthyl phosphonium salt 2b in only 5 minutes at room temperature using 1 mol% of CuI. Based on DFT calculations, the reaction is proposed to involve a Cu(i)/Cu(iii) cycle made of P-coordination, C-X oxidative addition and P-C reductive elimination. This copper-catalyzed route gives a general and efficient access to peri-bridged naphthyl phosphonium salts for the first time. Reactivity studies could thus be initiated and the possibility to insert gold into the strained P-C bond was demonstrated. It leads to (P,C)-cyclometallated gold(iii) complexes. According to experimental observations and DFT calculations, two mechanistic pathways are operating: (i) direct oxidative addition of the strained P-C bond to gold,(ii) backward-formation of the peri-halo naphthyl phosphine (by C-P oxidative addition to copper followed by C-X reductive elimination), copper to gold exchange and oxidative addition of the C-X bond to gold. Detailed analysis of the reaction profiles computed theoretically gives more insight into the influence of the nature of the solvent and halogen atom, and provides rationale for the very different behaviour of copper and gold in this chemistry.

International audience; The reactivity of a phenoxy-imine-ether system (FI)TiCl3/MAO was studied toward selective ethylene trimerization. This system was shown to either trimerize or polymerize ethylene depending on the reaction temperature. Its selectivity switches from a significant production of the trimerization product, 1-hexene (85 wt %, 520-450 kg1-hexene gTi-1 h-1) between 30 and 40 °C, to a moderate polyethylene formation (70-80 wt %, 60-70 kgpolyethylene gTi-1 h-1) at higher reaction temperature (T > 60 °C). Polymerization was investigated based on an original "polymer-to-catalyst" strategy aiming at identifying the active species responsible for this side reaction. Using DSC, SEC and high temperature 13 C NMR analyses, polyethylenes were found to exhibit high molar masses (> 10 5 g mol-1) and a low 1-hexene content (< 1 mol %) at any temperature. Kinetic studies support that trimerization and polymerization species are generated from the catalyst precursor at 40 °C but a parallel process may occur at higher temperature. The increase dispersity to 4.6 at 80 °C suggests a change from single to multisite catalysis. The poor comonomer incorporation ability of the active species is reminiscent of a molecular Ziegler Natta or a bulky postmetallocene catalyst.

Homogeneous olefin oligomerization plays a pivotal role in the field of petrochemistry. Through catalyst, technology, and process developments, market requirements in terms of productivity, selectivity and sustainability have been addressed. Over more than 50 years, intensive research has been devoted to the design of new Group 4 to Group 10 transition metal complexes and to the study of their reactivity towards olefins leading to several breakthroughs of prime importance for academia as well as for industry. Since the early 1960s, IFPEN contributed to bring innovative industrial solutions to different targets from gasoline production to alpha-olefin on purpose processes with over 100 production units built worldwide. Based on nickel, titanium, zirconium or chromium, the catalytic systems for such processes and their next generation are subject to continuous research where the adaptation of the ligand architecture to the nature of the metal and their mode of activation, play a crucial role to control the reaction selectivity and the catalyst lifetime. Interesting relationships between the complex structure and their reactivity have been drawn and will be discussed in selected examples.

The present paper describes the use of experimental designs (DoE) in association with high throughput experimentation devices for the optimization of cobalt hydroformylation of olefins in a biphasic system using ionic liquids. The main goal of the study was to gain insight into the various factors ([Co]NAIL , L/Co, Phorg /PhNAIL , pressure and temperature) and how they interact and influence the activity and selec-tivity of the catalyst. On the basis of a D-Optimal design, the study pointed out that temperature and to a less extend “Phaseorga /PhaseNAIL ” ratio are the most critical parameters. These conclusions confirm to a certain extend, the initial hypothesis formulated to describe the process operation. Furthermore, this strategy in association with high throughput experimentation devices, allows to predict catalytic results in the major part of a cubic space (representing the experimental domain) giving us the opportunity to determine the most suitable catalysts composition and optimal reaction conditions.

New imino-imidazole ligands bearing a pendant donor function L were synthesized in excellent yields. The corresponding nickel(II) complexes [NiCl2(imino-imidazole-L)]n (L = (CH2)2SMe (2a), (CH2)2OMe (2b), (CH2)2NEt2 (2c), (CH2)2PPh2 (2d), (C6H4)-p-OMe (2e), (CH2)3OMe (2f), (CH2)3CH3 (2g); n = 1, 2) were prepared and characterized by FT-IR spectroscopy and elemental analysis. Furthermore, the coordination geometry around the metal center in the dinuclear complex 2a and the mononuclear complexes 2c and 2e was unambiguously established by single crystal X-ray diffraction. All complexes have been evaluated for the oligomerization of ethylene in the presence of EtAlCl2 or MAO (methylaluminoxane) as cocatalyst, and mostly dimers and trimers were produced. Better activities were observed with EtAlCl2 as cocatalyst than with MAO.

The Bronsted acidity level was evaluated for ionic liquids to which a strong acid has been added. As a first approach, the evaluation method was based on the determination of the Hammett acidity functions H0 , using UV-Visible spectroscopy. The acidity of protons is mainly determined by their solvation state and consequently, the properties of protons depend on both the nature of the solvent and the nature and concentration of the acid. An apparent acidity scale was defined following this principle. It was found that, for the investigated ionic liquids, the cation does not play a dominant role on the acidity level ([BMIm] ~ [BHIm] ~ [ HNEt3 ] ), whereas changing the nature of the anion of the ionic liquid may lead to very different acidities ([ SbF6 ] > [ PF6 ] > [ BF4 ] > [ NTf2 ] > [OTf]). This “acidity scale” was tentatively compared with an “activity scale” obtained for the dimerization of isobutene into isooctenes. The tendencies concerning the cation effect were confirmed ([BMIm] ~ [BuMePyrr] ~ [ HNEt3 ] ). The anion effect in only partially validated with a different behaviour for NTf2 type ionic liquids ([ NTf2 ] ~ [ SbF6 ] > [ PF6 ] ~ [ BF4 ] > [OTf]). By an adequate choice of the ionic liquid, selectivity for isobutene dimers can reach 88 wt% (at 70% isobutene conversion) with possible recycling of the catalytic system without loss of activity and selectivity.

In our attempt to evaluate the acidity levels reached by acidified ionic liquids (BMImBF4, BMImNTf2 and BMImOTf + HOTf or HNTf2), the uncertainty on the pKas of the indicators needed for the Hammett spectrophotometric procedure was pointed out. As consequence another method is proposed, based on the H+/H2 couple potential measurement. In this purpose, if dynamic methods failed mainly for lack of sufficient reversibility, potentiometry with a hydrogen electrode gave meaningful results. The R0(H+) Strehlow function, could be calculated, using the Fc+-Fc couple as reference assumed as solvent independent. The obtained results show that i) the acidities are much higher than those in water; ii) the acidities measured by the hydrogen electrode are higher than those measured by the Hammett method; iii) the sequence of acidities for solutions of similar content of added acid is still BF4- > NTf2- > OTf- as previously measured with the Hammett method.

Hydroformylation of olefins has been performed with a system based on cobalt and pyridine ligands in non-aqueous ionic liquids. In this work, a new approach was developed to recycle the cobalt catalyst without the use of chemicals. For 1-hexene, activity of the [ Co2 (CO)8 ] /Pyridine(2 eq)/[BMIM][ NTf2 ] at 100 bar and 130°C can reach 110 h-1 with a selectivity for aldehydes of up to 87% (linear to branched ratio being around 1.8). The recycling of the ionic liquid phase was performed several times without loss of activity or selectivity.

International audience; Multinuclear aluminum cocatalysts have been obtained by the reaction of various phenols, alcohols or diois with trimethylaluminum and were used in situ or as isolated, welldefined species, for the activation of an iron(ll) or an iron(lll) precatalyst for the oligomerization of ethylene. The best cocatalyst candidate involves 2,2'-biphenol (10) in a 10/AIMe3 ratio of 2/3.

Ionic liquids are attracting a great deal of attention as possible replacement for conventional molecular solvents for catalytic and organic reactions. They complete the use of environmentally friendly water, supercritical fluids or perfluorinated solvents. Features that make ionic liquids attractive include their lack of vapor pressure and the great versatility of their chemical and physical properties. By a judicious combination of cations and anions, it is possible to adjust the solvent properties to the requirement of the reactions, thus creating an almost indefinitely set of “designer solvents”. Besides the possibility of recycling the catalytic system, one main potential interest in using ionic liquids results in the unique interactions of these media with the active species and in the possibility to modify the reaction activity and selectivity. Their successful use as solvents has been demonstrated for a wide range of organic reactions including acid catalyzed reactions and transition metal catalyzed transformations.

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