(Pyrazolyl)-(phosphinoyl)pyridine iron(II), cobalt(II) and nickel(II) complexes: Synthesis, characterization and ethylene oligomerization studies (original) (raw)
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Journal of Organometallic Chemistry, 2011
a b s t r a c t Reactions of [2-(3,5-dimethyl-pyrazol-1-yl)-ethanol] (L1) and [1-(2-chloro-ethyl)-3,5-dimethyl-1H-pyrazole] (L2) with Fe(II), Co(II), Ni(II), and Pd(II) salts gave the complexes [(L1) 2 FeCl 2 ] (1), [(L1) 2 CoCl 2 ] (2), [(L1) 2 NiBr 2 ] (3), [(L1) 2 Pd(Me)Cl] (5), [(L2) 2 CoCl 2 ] (6), and [(L2) 2 NiBr 2 ] . Whereas L2 behaves as a monodentate ligand, L1 can behave as either a monodentate or bidentate ligand depending on the nature of the metal centre. For palladium, L1 is monodentate in the solid state structure of 5 but bidentate in the structure of 4, obtained during attempts to crystallize 3. While the activation of iron, cobalt and palladium complexes with EtAlCl 2 did not produce active ethylene oligomerization catalysts, the nickel complexes 3 and 7 produced active ethylene oligomerization catalysts. Activities as high as 4329 kg/mol Ni h were obtained. Catalyst 3 produced mainly butenes (57%) and hexenes (43%); of which a combined 20% were converted to Friedel-Crafts alkylated-toluene. Catalyst 7, on other hand, produced mainly butenes (90%) and small amounts of hexenes (10%) which were then completely converted to the corresponding Friedel-Crafts alkylated-toluene products. This difference in product distribution in catalysis performed by complexes 3 and 7 is indicative of the role of the OH functionality in L1 on the EtAlCl 2 co-catalysts.
Organometallics, 2007
In this paper are described the synthesis, characterization, and coordinating properties of a new potentially pentadentate nitrogen ligand, CyAr2 N 5 , that combines in the same molecular structure 2,6-bis(imino)pyridine and (imino)pyridine moieties. This ligand reacts with 1 or 2 equiv of anhydrous MCl 2 (M) Fe, Co) to give paramagnetic mononuclear or homodinuclear complexes of the formula CyAr2 N 5 MCl 2 and CyAr2 N 5 M 2 Cl 4. In the dinuclear complexes, one metal center is five-coordinate, while the other is fourcoordinate. Ligand and metal complexes have been characterized, both in the solid state and in solution, by a variety of techniques, including single-crystal X-ray diffraction analyses, magnetic susceptibility determinations, IR, vis-NIR, 1 H NMR, and X-band EPR spectroscopies. On activation by methylaluminoxane (MAO) in toluene, the Fe II and Co II complexes generate effective catalysts for the oligomerization of ethylene to R-olefins with productivities and Schulz-Flory parameters depending on the type and number of the coordinated metals. In an attempt to rationalize the surprisingly high activity of the Co II precursors, and in particular that of the dinuclear derivative CyAr2 N 5 Co 2 Cl 4 , which is 4 times higher than that of the mononuclear analogue CyAr2 N 5 CoCl 2 , a Co II complex has been synthesized where the supporting ligand is sterically similar to CyAr2 N 5 , yet it contains only the three nitrogen donor atoms of the 2,6-bis-(imino)pyridine moiety. From this study, it is concluded that all five nitrogen atoms of CyAr2 N 5 play an active role under catalytic conditions, even when the precursor contains a free (imino)pyridine moiety.
Canadian Journal of Chemistry, 2005
Reactions of 2-furoyl chloride and 2-thiophene carbonyl chloride with substituted pyrazoles produced the modified pyrazolyl compounds: {(3,5-Me 2 pzCO)-2-C 4 H 3 O} (L1), {(3,5-Me 2 pzCO)-2-C 4 H 3 S} (L2), {(3,5-t-Bu 2 pzCO)-2-C 4 H 3 O} (L3), {(3,5-t-Bu 2 pzCO)-2-C 4 H 3 S} (L4), {(3,5-Ph 2 pzCO)-2-C 4 H 3 S} (L5), and {(pzCO)-2-C 4 H 3 O} (L6) in good yields. Reactions of these synthons with [Pd(NCMe) 2 Cl 2 ] afforded the corresponding mononuclear palladium(II) complexes: [Pd(L1) 2 Cl 2 ] (1), [Pd(L2) 2 Cl 2 ] (2), [Pd(L3) 2 Cl 2 ] (3), [Pd(L4) 2 Cl 2 ] (4), [Pd(L5) 2 Cl 2 ] (5), and [Pd(L6) 2 Cl 2 ] in moderate to high yields. All compounds synthesized were characterized by a combination of 1 H NMR, 13 C NMR, and IR spectroscopy. Compounds L1, 1, and 2 were examined by single crystal X-ray crystallography. DFT theoretical studies at the B3LYP/6-31+G(d) level of theory with GAUSSIAN98 have been used to rationalize some of the results. When the complexes were activated with ethylaluminium dichloride (EtAlCl 2 ), they catalysed the oligomerization of ethylene to mostly C 10 and C 12 oligomers. Oligomer distribution greatly depends on the oligomerization conditions; for example, an increase in temperature and pressure produced a higher percentage of C 12 compared to C 10 .
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, 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.
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, 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.
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.