A catalytic and DFT study of selective ethylene oligomerization by nickel(II) oxime-based complexes (original) (raw)
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Dalton Transactions, 2008
The dinuclear complexes [Ni(l-Cl){(4,5-dihydro-4,4-dimethyloxazol-2-yl)methanol}] 2 Cl 2 14 and [Ni(l-Cl){(pyridin-2-yl)methanol}] 2 Cl 2 16 have been synthesized in high yields by reaction of NiCl 2 with 2 mol. equiv. of the ligands 4,5-dihydro-4,4-dimethyloxazol-2-yl)methanol 13 or (pyridin-2-yl)methanol 15, respectively. The reaction of NiCl 2 with 3 mol. equiv. of 15 afforded in high yield the mononuclear, octahedral mer-[Ni{(pyridin-2-yl)methanol} 3 Cl 2 ] complex 18. The reaction of 16 with NaH led to the deprotonation of one of the pyridine alcohol ligands to form [Ni{(pyridin-2-yl)methanol}{(pyridin-2-yl)methanolate}Cl] 21 in which the metal is coordinated by one pyridine alcohol and one pyridine alcoholate ligand. The crystal structures of the dinuclear, chloride-bridged octahedral complexes in 14·C 6 H 12 and in 16·3CH 2 Cl 2 and of the mononuclear, octahedral complex 18 in 18·CH 2 Cl 2 have been determined by X-ray diffraction. In the latter case, intermolecular OH · · · Cl bonding interactions generate a centrosymmetric pseudo-dimer. Complexes 14, 16 and 21 have been tested in ethylene oligomerization with AlEtCl 2 (Al/Ni ratios of 2, 4 or 6) or MAO (50, 100 or 200 equiv.) as co-catalysts under 10 bar of ethylene and yielded mostly dimers and trimers. Complex 16 in the presence of 6 equiv. of AlEtCl 2 proved to be the most active system with a turnover frequency (TOF) up to 187 500 C 2 H 4 (mol Ni h) −1 . Complex 16 with 200 equiv. of MAO was also the most active, with TOF up to 104 300 C 2 H 4 (mol Ni h) −1 under 30 bar of ethylene.
Inorganic Chemistry, 2004
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-6methyl-[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(µ-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 singlecrystal 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 50 000 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 R-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.
Dalton transactions (Cambridge, England : 2003), 2014
A series of N-alkyl 2,2'-dipyridylamine ligands of general formula (2-C5H3NR)2NR', (a): R = H, R' = Me; (b): R = H, R' = benzyl; (c): R = H, R' = methylcyclohexyl; (d): R = H, R' = neopentyl; (e): R = Me, R' = Me) were prepared by a modified method involving base-mediated N-alkylation with the respective alkyl halide. Reaction of the ligands, a-e, with NiCl2(DME) allowed for the isolation of μ-Cl Ni(ii) complexes: [Ni(μ-Cl){a}Cl]2 (1a); [Ni(μ-Cl){b}Cl]2 (1b); [Ni(μ-Cl){c}Cl]2 (1c); [Ni(μ-Cl){d}Cl]2 (1d) and [Ni(μ-Cl){e}Cl]2 (1e). The complexes were characterised by FT-IR spectroscopy, magnetic susceptibility measurements, mass spectrometry, elemental analyses and in the case of 1a, SCD analysis. In the case of complex 1e, an acid-mediated hydrolysis process was identified. The product of hydrolysis, the protonated ligand and a tetrachloronickelate salt (1e-A), was characterised by SCD analysis. Activation of 1a-1e with alkyl aluminium reagents generated h...
Inorganica Chimica Acta, 2013
A new family of nickel(II) complexes of the type [Ni(PA)(L)(CH 3 CN) n ]BPh 4 1-5, where n = 1, 2, H(PA) is 2-picolinic acid and L is N,N 0-tetramethylethylenediamine (L1) 1, N,N 0 ,N 00-pentamethyldiethylenetriamine (L2) 2, 2,2 0-bipyridine (L3) 3, 1,10-phenanthroline (L4) 4 or 2,9-dimethyl-1,10-phenanthroline (L5) 5, has been isolated and characterized using CHN analysis, UV-Vis spectroscopy and ESI-MS. The complex [Ni(PA)(L2)(CH 3 CN)](BPh 4) 2 possesses a distorted octahedral coordination geometry in which Ni(II) is chelated to 2-picolinate anion and L2. DFT calculations show that trans isomers of 3-5 are more stable than cis isomers by ca. 4.0 kJ/mol. In contrast, cis-1 is more stable than trans-1 by 15.8 kJ/mol. The complexes catalyze the hydroxylation of cyclohexane efficiently in presence of m-CPBA as oxidant with 244-569 turnover numbers and good alcohol selectivity (A/K, 3.4-7.0). Adamantane is oxidized to 1-adamantanol, 2-adamantanol and 2-adamantanone with varying bond selectivity (3°/2°, 9.3-14.2) while cumene is selectively oxidized to 2-phenyl-2-propanol. Upon replacing bidentate L1 by tridentate L2 or strongly p-back bonding phen the catalytic activity increases. In contrast, phen is replaced by non-planar bpy or 2,9-dmp with sterically hindering methyl groups the catalytic activity decreases. Thus ligand denticity, Lewis acidity of Ni(II) center and p-back bonding determine the catalytic activity.
Nitrogen-donor late transition metal complexes as ethylene oligomerization catalysts
2016
Over the past few years, interest has grown in developing a new generation of catalysts with greater selectivity for the desired range of linear α-olefins. At the center of these developments have been late transition metal complexes. The architecture of the ligands in the complex structures plays a crucial role. Although the interplay between electronic and steric properties of the ligands have long been recognized as essential in determining the catalytic performance of these complexes, accurate predictions still remain a major challenge. The main areas of interest are catalyst activity, selectivity and stability. The quest to strike a balance between these key catalyst properties underlies the rationale of this research study. This thesis is made up of seven chapters. Chapter 1 covers the introduction of olefin catalysis; highlighting the industrial manufacture and commercial applications of olefins and the role played by late-transition metals in these processes. Chapter 2 reviews the relevant literature on late transition metal catalysts towards ethylene oligomerization reactions. Recent developments associated with late-transition metal complexes, in particular nickel(II), cobalt(II), iron(II) and palladium(II) complexes, are discussed. Chapter 3 describes the syntheses of 2-(chloromethyl)-6-(pyrazol-1-ylmethyl)pyridine nickel(II), cobalt(II) and iron(II) complexes and their catalytic behaviour in ethylene oligomerization reactions. The study focused on the role of co-catalyst and solvent in ethylene oligomerization reactions using EtAlCl2 and MAO co-catalysts and toluene, hexane and vi chlorobenzene solvents. The findings of this chapter have been published in
Organometallics, 2009
The complex [NiCl 2 {Ph 2 POCH 2 ox Me2 }] (Ph 2 POCH 2 ox Me2 ) 2-((diphenylphosphinooxy) methyl)-4,4dimethyl-4,5-dihydrooxazole) 14 has been synthesized by reaction of solid [NiCl 2 (DME)] (DME ) 1,2dimethoxyethane) with a CH 2 Cl 2 solution of the P,N ligand. X-ray diffraction studies on its red crystals established the mononuclear nature of the complex 14a, whose metal center has a distorted tetrahedral coordination geometry. Recrystallization of 14a from a toluene-pentane/CH 2 Cl 2 solution at temperatures below 253 K afforded green crystals of the dinuclear, chloride-bridged, formula isomer complex 14b. Conversion of 14b to 14a was observed as a function of temperature, both in the solid-state and in solution. Together with other Ni(II) complexes containing a chelating P,N ligand of the type phosphinoor phosphinito-oxazoline or phosphino-thiazoline, 14a has been evaluated as precatalyst in the oligomerization of ethylene, with AlEtCl 2 or MAO as cocatalyst, or propylene, with MAO as cocatalyst. With AlEtCl 2 as activator (6 equiv), the catalytic activities with ethylene were generally modest and [NiCl 2 {Ph 2 PCH 2 ox}] (Ph 2 PCH 2 ox ) 2-((diphenylphosphinooxy)methyl)-4,5-dihydrooxazole) 1 was the most active, with turnover frequencies (TOF) up to 7.9 × 10 4 mol of C 2 H 4 (mol Ni × h) -1 , whereas 14a, activated with 2 equiv of AlEtCl 2 , was the most selective for ethylene dimers (up to 96%) and 1-butene (up to 22%). With MAO as cocatalyst, complex 1 was again the most active, with TOF values up to 23 × 10 4 mol of C 2 H 4 (mol Ni × h) -1 . The highest selectivity for butenes was observed with complex [NiCl 2 {Ph 2 PCH 2 thiaz Me2 }] 3. With propylene, TOFs up to 3.3 × 10 4 mol of C 3 H 6 (mol Ni × h) -1 were obtained with [NiCl 2 {Ph 2 POCH 2 pyridine}] 8 and selectivities for C 6 products higher than 98.5% were observed with precatalysts 3, [NiCl 2 {t-Bu 2 POCH 2 pyridine}] 9, and 14a.
Organometallics, 2004
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 R to P were used for the synthesis of the paramagnetic Ni(II) complexes [NiCl 2 (P,N)] 9-11, respectively. The complex 11‚0.5CH 2-Cl 2 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 C 2 H 4 /mol Ni‚h (11) in the presence of only 6 equiv of AlEtCl 2. The selectivity for C 4 olefins reached 81% for 9 in the presence of 2 equiv of AlEtCl 2 , 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 AlEtCl 2 as cocatalyst but higher selectivities for 1-butene. A turnover frequency of 22 800 mol C 2 H 4 /mol Ni‚h was observed for 11 in the presence of 800 equiv of MAO. The selectivities were in the range 70-85% for the C 4 olefins and in the range 33-38% for 1-butene within the C 4 fraction. For these P,N ligands, increasing the degree of alkyl substitution at the carbon R to P leads to higher activities for ethylene oligomerization and more selective formation of R-olefins. The nature of the N-heterocycle influences the activity, as shown by the turnover frequencies of 58 100 mol C 2 H 4 /mol Ni‚h for 11 in the presence of 6 equiv of AlEtCl 2 and 45 900 mol C 2 H 4 /mol Ni‚h for the related phosphinooxazoline complex 16. Under these conditions, the selectivity to 1-butene within the C 4 fraction was 11% for 11 and 20% for 16. When MAO was used as a cocatalyst (800 equiv), a similar trend was observed for the activity, but the selectivity to 1-butene within the C 4 fraction increased to 38% for 11 and 37% for 16.
Accounts of Chemical Research, 2005
Catalytic ethylene oligomerization represents a topic of considerable current academic and industrial interest, in particular for the production of linear R-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.
Organometallics, 2004
The new phosphinopyridine ligands rac-2- [(diphenylphosphanyl)benzyl]pyridine (6), rac-2-[1′-(diphenylphosphanyl)ethyl]pyridine , and 2-[1′-(diphenylphosphanyl)-1′-methyl]ethylpyridine (8) with variable substitution at the carbon R to P were used for the synthesis of the paramagnetic Ni(II) complexes [NiCl 2 (P,N)] 9-11, respectively. The complex 11‚0.5CH 2 -Cl 2 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 C 2 H 4 /mol Ni‚h in the presence of only 6 equiv of AlEtCl 2 . The selectivity for C 4 olefins reached 81% for 9 in the presence of 2 equiv of AlEtCl 2 , 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 AlEtCl 2 as cocatalyst but higher selectivities for 1-butene. A turnover frequency of 22 800 mol C 2 H 4 /mol Ni‚h was observed for 11 in the presence of 800 equiv of MAO. The selectivities were in the range 70-85% for the C 4 olefins and in the range 33-38% for 1-butene within the C 4 fraction. For these P,N ligands, increasing the degree of alkyl substitution at the carbon R to P leads to higher activities for ethylene oligomerization and more selective formation of R-olefins. The nature of the N-heterocycle influences the activity, as shown by the turnover frequencies of 58 100 mol C 2 H 4 /mol Ni‚h for 11 in the presence of 6 equiv of AlEtCl 2 and 45 900 mol C 2 H 4 /mol Ni‚h for the related phosphinooxazoline complex 16. Under these conditions, the selectivity to 1-butene within the C 4 fraction was 11% for 11 and 20% for 16. When MAO was used as a cocatalyst (800 equiv), a similar trend was observed for the activity, but the selectivity to 1-butene within the C 4 fraction increased to 38% for 11 and 37% for 16.