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In this article are summarized the different mechanistic pathways for the oligomerization of monoolefins by homogeneous catalysts, particularly for ethylene and alpha olefins. The major topics are: the production of non regioselective and also regioselective olefin dimers, the production of linear alpha olefins by ethylene oligomerization as well as the selective dimerization of ethylene and its selective trimerization. Several industrial developments initiated by IFP are presented to illustrate this topic.

International audience; Chromium(III) complexes bearing R'N(CH2PR2)2 (PCNCP) ligands were prepared. Upon activation with methylaluminoxane, these complexes proved to be effective in the selective tri- and tetramerization of ethylene. The formation of either 1-hexene or 1-octene was found to be highly dependent on the steric bulk of the substituents R on the phosphine moieties. This observation was rationalized using density functional theory calculations on selected steps of the metallacyclic mechanism of the ethylene oligomerization reaction.

We report on the synthesis of mono(aryloxido)titanium(IV) complexes of general formula {Ti[O(o-R)Ar]X3}, with X = OiPr, ArO = 2-tert-butyl-4-methylphenoxy and R = CMe3 (2a), CMe2Ph (2b) and CH2NMe2 (2c). Attempts to reach pure mono(aryloxido) complexes when R = CH2NMe(CH2Ph) (2d) or CH2N(CH2Ph)2 (2e) were unsuccessful. When R = CH2OMe, the analogous mononuclear complex was not obtained, and instead, a dinuclear complex [(2-tert-butyl-4-methyl-6-methoxymethylphenoxy) TiCl(OiPr)(μ2-OiPr)2TiCl(OiPr)2] (3) was formed. Complexes 2b and 3 were characterized by single-crystal X-ray diffraction. The former contains a tetrahedrally coordinated TiIV centre, whereas in the latter the aryloxido ligand behaves as a chelating–bridging ligand between the two, chemically very different metal centres that form two face-sharing octahedra. Different synthetic approaches starting from [Ti(OiPr)4] or [TiCl(OiPr)3] were evaluated and are discussed. The hemilabile behaviour of the aryloxido ligand resulting from reversible coordination of its side arm was studied by variable-temperature 1H NMR spectroscopy for 2c (R = CH2NMe2). Complexes 2a–d were contacted with ethylene and AlEt3 as cocatalyst. When activated with AlEt3 (3 equiv.) at 20 bar and 60 °C, complex 2c exhibits interesting activity (2100 g/gTi/h) for the selective dimerization of ethylene to 1-butene (92 % C4=; 99+% C4=1). Noticeable differences in catalyst activity were observed when the R group was modified. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

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.

Nickel(II) diphenylphosphinoenolate complexes have been prepared from (ortho-HX-substituted benzoylmethylene)triphenyl phosphoranes (X = NMe, NPh) and [Ni(1,5-cod)2] in the presence of a tertiary phosphine (PPh3 or P(p-C6H4F)3). An X-ray diffraction study of the complexes 10 and 16 establishes the presence of strong intramolecular hydrogen bonding between the enolate oxygen and the N–H function, as originally found in 11. This feature favours the formation of the desired shorter-chain-length products in the catalytic oligomerisation of ethylene. To cite this article: P. Braunstein et al., C. R. Chimie 8 (2005).

The new phosphinopyridine ligands 2-[(diphenylphosphanyl)methyl]-6-phenylpyridine (5), 2-(2,6-dimethylphenyl)-6-[(diphenylphosphanyl)methyl]pyridine (6), 2-(2,6-diisopropylphenyl)-6-[(diphenylphosphanyl)methyl]pyridine (7), and 2-[2-(diphenylphosphanyl)phenyl]-6-methylpyridine (8) have ben prepared in order to compare the influence of their stereoelectronic properties on the catalytic behavior of their respective mononuclear [NiCl2(P,N)] complexes 9−12. These Ni(II) complexes are paramagnetic in solution, as determined by the Evans method. Whereas they were inactive for the oligomerization of ethylene in the presence of methylalumoxane (MAO), they provided activities up to 61 000 mol of C2H4/((mol of Ni) h) (11) in the presence of only 6 equiv of AlEtCl2. The selectivities for C4 olefins were as high as 92% (12 with 2 equiv of AlEtCl2).

The phosphinooxazoline ligands 9−12 have been prepared and used to examine and compare the catalytic properties of their corresponding Ni(II) complexes in ethylene oligomerization. The molecular structure of rac-2-[1‘-(diphenylphosphanyl)ethyl]-4,4-dimethyl-4,5-dihydrooxazole (10) has been determined by X-ray diffraction. The paramagnetic Ni(II) complexes [NiX(μ-X)(P,N)]2 (19, X = Br, P,N = 2-[(diphenylphosphanyl)methyl]-4,4-dimethyl-4,5-dihydrooxazole (9)); 20, X = Cl, P,N = 9; 21, X = Cl, P,N = 10); 22, X = Cl; P,N = 2-[(diphenylphosphanyl)methyl]-4-(R)-phenyl-4,5-dihydrooxazole (12)); 23, X = Br, P,N = 12) and [NiCl2(P,N)] (24; P,N = 2-[1‘-(diphenylphosphanyl)-1‘-methylethyl]-4,4-dimethyl-4,5-dihydrooxazole (11)) were prepared in yields of 79−90%, and 19 and 24 have been characterized by X-ray diffraction. The former is a dinuclear complex with distorted-trigonal-bipyramidal geometry around the Ni(II) centers, whereas 24 is a mononuclear, tetrahedral complex, which underlines the strong influence of a ...

The new phosphinopyridine ligands rac-2-[(diphenylphosphanyl)benzyl]pyridine (6), rac-2-[1‘-(diphenylphosphanyl)ethyl]pyridine (7), and 2-[1‘-(diphenylphosphanyl)-1‘-methyl]ethylpyridine (8) with variable substitution at the carbon α to P were used for the synthesis of the paramagnetic Ni(II) complexes [NiCl2(P,N)] 9−11, respectively. The complex 11·0.5CH2Cl2 has been shown by X-ray diffraction to have an almost planar coordination geometry about the metal, although the coordination sphere of all complexes in solution was determined by the Evans method to be distorted tetrahedral. The Ni complexes provided activities for the catalytic oligomerization of ethylene up to 58 100 mol C2H4/mol Ni·h (11) in the presence of only 6 equiv of AlEtCl2. The selectivity for C4 olefins reached 81% for 9 in the presence of 2 equiv of AlEtCl2, but the selectivity toward 1-butene was only 11−14%. In the presence of 400 or 800 equiv of methylalumoxane (MAO), complexes 9−11 yielded lower activities than with AlEtCl2 as cocat...

The bis(oxazolinyl)phenylphosphonite ligand (bis(4,4-dimethyl-2-(1-hydroxy-1-methylethyl)-4,5-dihydrooxazole)phenylphosphonite, NOPONMe2)) and the new pyridine-phosphonite ligand (2-ethyl(1'-methyl-1-hydroxy)pyridine-6H-dibenz[c,e][1,2]oxaphosphorin) have been used for the preparation of the mononuclear complexes [NiCl2(NOPONMe2)] 18 and [NiCl2(6)2] 19, respectively, which catalyze the oligomerisation of ethylene with activities up to 57300 mol C2H4 mol Ni(-1) h(-1) (19 in the presence of only 6 equivalents of AlEtCl2). The selectivities for C4 dimers were as high as 90% (18 in the presence of only 2 equivalents of AlEtCl2) with selectivities for 1-butene of 21-22% of the C4 fraction. In the presence of 400 or 800 equivalents of MAO as cocatalyst, complex 19 yielded turnover frequencies of 7400 mol C2H4 mol Ni(-1) h(-1) and 13200 mol C2H4 mol Ni(-1) h(-1), respectively. The selectivities for 1-butene and ethylene dimers were similar to those obtained with AlEtCl2. The fact that 19 with a cyclic phosphonite moiety leads to higher activities and selectivities than 18 which contains an acyclic phosphonite group underlines the importance of the ligand on the catalytic properties of its metal complex. An unprecedented dinuclear iron complex [FeCl2(4,4-dimethyl-2-[(1-hydroxy-1-methyl)ethyl]-4,5-dihydrooxazolate)]2 20 was also obtained which contains two pentacoordinated metal centers coordinated by a bridging-chelating oxazoline-alcoholate. Complexes 18-20 are paramagnetic in solution, as determined by the Evans method.

Bis-aryloxyalkylaluminium complexes, previously involved in the synthesis of aryloxyaluminium perrhenate complexes that are active in olefin metathesis in homogeneous phase, are able to increase the activity of the supported Re 2 O 7 /Al 2 O 3 metathesis catalyst. They are also able to make active an otherwise inactive low temperature-treated Re 2 O 7 /Al 2 O 3 catalyst. They can be used to regenerate, for the first time at room temperature, a previously deactivated catalyst. Until now, a high temperature calcination treatment was essential for the regeneration. These properties are attributed to the strong Lewis acidic character of these aluminium complexes due to the low coordination state of the aluminium, protected by the aryloxy ligands.

The complexes [[graphic omitted]Ph)Ph}{Ph3PCHC(NPh)Ph-N}] and [[graphic omitted]Ph)Ph}(PR3)](PR3= PMe3, PMe2Ph or PMePh2) were prepared starting from [Ni(cod)2](cod = cycloocta-1,5-diene) and the phosphorus ylide Ph3PCHC(NPh)Ph I in the presence of a tertiary phosphine. Surprisingly, only the first complex was isolated when PPh3 and P(C6H11)3 were used, whereas the other phosphines led to the corresponding PR3 complexes together with variable amounts of the first depending on their steric demand. The known synthesis of I has been optimized to yields close to 90%. Experiments carried out to study the potential of the nickel compounds as catalysts for ethylene oligomerization showed the stoichiometric formation of styrene and minor amounts of low-molecular-weight linear α-olefins. The molecular structures of I and the first complex have been determined by X-ray diffraction. In the nickel complex the coordination around the metal is distorted square planar, with P(1)–Ni–C(1) and N(1)–Ni–N(2) angles of 90.30(8) and 97.18(8)°, respectively.

In this article are summarized the different mechanistic pathways for the oligomerization of monoolefins by homogeneous catalysts, particularly for ethylene and alpha olefins. The major topics are: the production of non regioselective and also regioselective olefin dimers, the production of linear alpha olefins by ethylene oligomerization as well as the selective dimerization of ethylene and its selective trimerization. Several industrial developments initiated by IFP are presented to illustrate this topic.

Neodymium trichloride reacts with 2 equiv. of the lithium salt of 9-(cyclopentadienyl-1-methylethyl)-9,10-dihydroanthracene in THF to give the “ate” complex [Li(THF)4][Nd{(C5H4)CMe2 (C14H10)}2] which has been characterized by its crystal structure and elemental analysis. The neodymium atom is situated in tetrahedral environment. It is η5-bonded to the two cyclopentadienyl rings and σ-bonded to the C(10) atoms of the two dihydroanthracene moieties.

Biphenylene reacts with activated Sm and Yb powders in ethers giving 2,2′-biphenyldiyl-Smi II and -Yb II complexes by opening of the C 4 ring. They have been characterized by reactions with electrophiles such as the proton and dimethyldichlorosilane, and by 1 H, 13 C and 171 Yb NMR measurements. The Yb complex can be obtained by reaction of 2,2′-dilithiobiphenyl with Yb I 2 . Octamethylbiphenylene, the reduction potential of which is much more negative than that of biphenylene, does not react with Yb powder. In contrast, tricarbonyloctamethylbiphenylenechromium reacts with metal powder due to the presence of the electron-withdrawing Cr(CO) 3 group. This suggests that an electron transfer from the metal precedes the opening of the cyclobutane ring.

A wide range of ionic liquids based on imidazolium and pyrrolidinium cations and weakly coordinating anions proved to be efficient solvents for the biphasic rhodium catalyzed hydroformylation of 1-hexene; the reaction rate and regioselectivity, and the retention of the rhodium can be optimized by fitting the nature of the anions and cations of the ionic liquid and the modified phosphite or phosphine ligands.

In the oxidative carbonylation of ethylene by carbon monoxide and butyl nitrite catalyzed by PdCl{sub 2}(PhCN){sub 2} in the presence of triphenylphosphine, the pentacoordinated tetravalent palladium complex PdCl{sub 2}(COOBu)NO(PPh{sub 3}) has been isolated and has proved to be an intermediate in the catalytic cycle.

In the 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ionic liquid ([BMI][NTf(2)]), [Co(NTf(2))(2)] is reduced under 5.5 MPa of H(2)-CO to [Co(2)(CO)(8)] prior to [HCo(CO)(4)], provided a pyridine ligand is present in the medium.

Catalytic ethylene oligomerization represents a topic of considerable current academic and industrial interest, in particular for the production of linear alpha-olefins in the C4-C10 range, whose demand is growing fast. Identifying and fine-tuning the parameters that influence the activity and selectivity of metal catalysts constitute major challenges at the interface between ligand design, coordination/organometallic chemistry, and homogeneous catalysis. In this Account, we show how comparative studies aiming at modulating the coordinating properties of functional ligands for a metal, such as nickel, which is used in industrial processes, lead to beneficial effects in catalytic ethylene oligomerization.

The new dicationic dinuclear complexes [Ni(micro-Cl)(2)(N,OH)(2)]Cl(2) (11, N,OH = 2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)-propan-2-ol; 12, N,OH = 2-pyridin-2-yl-propan-2-ol) were prepared in good yields and evaluated as precatalyts in the oligomerization of ethylene, using MAO or AlEtCl(2) as cocatalyst. These paramagnetic complexes were characterized by single-crystal X-ray diffraction in the solid state and in solution with the help of the Evans method, which revealed agreement between the octahedral coordination spheres found in solution and in the solid state. The N donor atoms of each chelating ligand are in mutual cis position, and the OH donors are mutually trans situated. Selectivities for 1-butene within the C(4) fraction of 61% (11) and 58% (12) were observed in the presence of 200 equiv of MAO, but better turnover frequencies (28 300 (11) and 20 400 (12) mol of C(2)H(4)/(mol of Ni.h)) were obtained when 800 equiv of MAO was used. In the presence of 6 equiv of AlEtCl(2), the activities were considerably increased, up to 174 300 (11) and 97 100 (12) mol of C(2)H(4)/(mol of Ni.h), and the selectivity for C(4) olefins was 70% and 64%, respectively.

The phosphinitooxazoline 4,4-dimethyl-2-[1-oxy(diphenylphosphine)-1-methylethyl]-4,5-dihydrooxazole (9), the corresponding phosphinitopyridine ligands 2-ethyl-[1'-methyl-1'-oxy(diphenylphosphino)]pyridine (11) and 2-ethyl-6-methyl-[1'-methyl-1'-oxy(diphenylphosphino)]pyridine (12), which have a one-carbon spacer between the phosphinite oxygen and the heterocycle, and the homologous ligand 2-propyl-[2'-methyl-2'-oxy(diphenylphosphino)]pyridine (13), with a two-carbon spacer, were prepared in good yields. The corresponding mononuclear [NiCl(2)(P,N)] complexes 14 (P,N = 9), 15 (P,N = 11), and 16 (P,N = 12) and the dinuclear [NiCl(micro-Cl)(P,N)](2) 17 (P,N = 13) Ni(II) complex were evaluated in the catalytic oligomerization of ethylene. These four complexes were characterized by single-crystal X-ray diffraction in the solid state and in solution with the help of the Evans method, which indicated differences between the coordination spheres in the solution and the solid state. In the presence of methylalumoxane (MAO) or AlEt(3), only the decomposition of the Ni complexes was observed. However, complexes 14-17 provided activities up to 50000 mol C(2)H(4)/(mol Ni).h (16 and 17) in the presence of only 6 equiv of AlEtCl(2). The observed selectivities for ethylene dimers were higher than 91% (for 14 or 15 in the presence of only 1.3 equiv of AlEtCl(2)). The activities for 14-17 were superior to that of [NiCl(2)(PCy(3))(2)], a typical dimerization catalyst taken as a reference. The selectivities of the complexes 14-17 for ethylene dimers and alpha-olefins were the same order of magnitude. From the study of the phosphinite 9/AlEtCl(2) system, we concluded that in our case ligand transfer from the nickel atom to the aluminum cocatalyst is unlikely to represent an activation mechanism.

A wide range of ionic liquids based on imidazolium and pyrrolidinium cations and weakly coordinating anions proved to be efficient solvents for the biphasic rhodium catalyzed hydroformylation of 1-hexene; the reaction rate and regioselectivity, and the retention of the rhodium can be optimized by fitting the nature of the anions and cations of the ionic liquid and the modified phosphite or phosphine ligands.

International audience; Bis(aminophoshonium) salts derived from bis(diphenylphosphino)methane were prepared and triply deprotonated with potassium hexamethyldisilazane to yield the corresponding bis(iminophosphoranyl)methanides, which were then subjected to coordination with CrIIICl3(THF)3. Binuclear complexes of type [(HC(PPh2NR)2Cr(-Cl)(Cl))2] (R = iPr, tBu) with an octahedral coordination geometry and a long C–Cr bond were obtained and structurally characterized. In the case of R = o-MeO-C6H4, a monomeric species featuring no C–Cr bond is observed. Preliminary evaluation of catalytic activities of these complexes in ethylene oligomerization and polymerization is reported.

Novel manganese (III) μ-oxo complexes with the formula Mn2IIIO(C3F7CO2)4(bipy)2 ( 1 ) were synthesized from the oxidation of

Nickel diphenylphosphinoenolate complexes are prepared from ortho-HX-substituted phenacylidenetriphenylphosphoranes (X = O, NMe, NPh) which display strong intramolecular hydrogen bonding between the enolate oxygen and the H–X function; this feature dramatically influences the molecular mass distribution of the oligomers obtained by catalytic oligomerisation of ethene.

α-Chloronitriles are shown to add to α-olefins and conjugated dienes, with ferrous chloride or preferably cuprous chloride in the presence of 2,2′-bipyridyl or 1,10-phenanthroline as catalysts

The reaction of dienes with arenesulphinic acids or sodium arenesulphinates in acetic acid in the presence of palladium catalysts gives high yields of allylic sulphones containing large proportions of (sometimes exclusively) the more substituted isomer.

The reaction of aromatic ketones with rare earth metals in 1,2-dimethoxyethane produces, by hydrolysis, the corresponding alcohols, pinacols and hydrocarbons depending on the metal, the ketone and the molar ratio of the reactants. The formation of the various reduced products is reversible.

Cupric salts, particularly triflates, convert α-sulphonyl carbanions into α-disulphones. Allylphenylsulphones couple preferentially in the 3-3′ mode.

Novel oxoperoxomolybdenum(VI) complexes with the general formula MoO(O2)L2X2 (III, L = DMF, HMPT) and MoO(O2)Cl(ON)L(IV, ON) = pyridin-2-carboxylate (Pic), 8-hydroxyquinolinate (Quin) were prepared from the reaction of Ph3COOH or H2O2 with the corresponding cis-dioxo complexes. In the reaction with Ph3COOH both oxygen atoms of the peroxo moiety were found, by 18O labeling experiments, to come from the hydroperoxide. The X-ray crystal structure of MoO(O2)Cl(Pic)(HMPT) revealed a bipyramidal pentagonal surounding with a rather short OO distance (1.41 A). Complexes III were found to be more reactive than MoO(O2)2,HMPT for the epoxidation of olefins (oxidative cleavage products are consecutively formed) but react by the same cyclic peroxymetalation mechanism. The absence of reaction in the case of complexes IV illustrates the necessity for the metal to possess an equatorial releasable coordination site adjacent to the peroxo group for the oxygen transfer to occur. Catalytic oxidation of olefins using Ph3COOH gave a selectivity in oxygenated products very different from that using t-BuOOH, and 18O labeling studies showed that alkyl-peroxidic rather than peroxo species are intermediates in this latter reaction. The mechanism of epoxidation of olefins by alkyl hydroperoxides catalyzed by d0 metal complexes is discussed.

α-Chloroesters add to olefins or dienes under redox catalysis by cuprous chloride in the presence of Bipy or Phen, leading to γ-chloroesters or unsaturated esters.

Benzyl chloride is shown to add to olefins in DMF in the presence of CuCl/bipyridyl, CuCl/phenanthroline or FeCl 2 . Addition of p -nitrobenzyl chloride takes place under milder conditions.

The reaction of rare-earth metals such as cerium, neodymium, samarium and ytterbium with unsaturated hydrocarbons and aromatic ketones having various electronic affinities was investigated. Ytterbium is the most reactive. The cleavage of the carbon-carbon bonds and carbon-oxygen bonds by ytterbium and samarium is also described.

The reaction of rare-earth metals such as cerium, neodymium, samarium and ytterbium with unsaturated hydrocarbons and aromatic ketones having various electronic affinities was investigated. Ytterbium is the most reactive. The cleavage of the carbon-carbon bonds and carbon-oxygen bonds by ytterbium and samarium is also described.

Les complexes peroxo du chrome(IV) CrO 5 L (L=Et 2 O,Ph 3 PO) sont capables d'oxyder les hydrocarbures en alcools et en produits carbonyles correspondants. Une faible activite pour l'epoxydation des olefines et l'hydroxylation des noyaux aromatiques est observee. L'espece oxydante pourrait etre une espece biradicalaire Cr v -O-O • principalement capable d'arracher un atome d'hydrogene au substrat