Catalytic Ethylene Oligomerization Research Articles

N-Phosphanyl- and N,N′-Diphosphanyl-Substituted N-Heterocyclic Carbene Chromium Complexes: Synthesis, Structures, and Catalytic Ethylene Oligomerization

The chromium(II) complexes [CrCl2(t-BuNHC,P-κC)2] (1), [CrCl2(MesNHC,P-κC)2] (2), [CrCl2(DippNHC,P-κC)2] (3), and [CrCl2(P,NHC,P-κC)2] (4) containing the N-phosphanyl- or N,N′-diphosphanyl-substituted N-heterocyclic carbene (NHC) hybrid ligands t-BuNHC,P (1-(di-tert-butylphosphino)-3-tert-butylimidazol-2-ylidene), MesNHC,P (1-(di-tert-butylphosphino)-3-mesitylimidazol-2-ylidene), DippNHC,P (1-(di-tert-butylphosphino)-3-(2,6-diisopropylphenyl)imidazol-2-ylidene), and P,NHC,P (1,3-bis(di-tert-butylphosphino)imidazol-2-ylidene), respectively, were prepared from CrII ([CrCl2(thf)2]) or CrIII ([CrCl3(thf)3] or [Cr(Me)Cl2(thf)3]) precursors. The solid-state structures of these four complexes show square-planar CrII centers, with two trans chloride and two monodentate CNHC donors. Alkylation of 3 and 4 with [Mg(benzyl)2(thf)2] led to the formation of the σ complexes [Cr(benzyl)3(DippNHC,P-κC,κP)] (5) and [Cr(benzyl)3(P,NHC,P-κC,κP)] (6), respectively, with five-coordinate distorted-square-pyramidal CrIII coordin...

Unsymmetrical Chelation of N-Thioether-Functionalized Bis(diphenylphosphino)amine-Type Ligands and Substituent Effects on the Nuclearity of Iron(II) Complexes: Structures, Magnetism, and Bonding.

Starting from the short-bite ligands N-thioether-functionalized bis(diphenylphosphino)amine-type (Ph2P)2N(CH2)3SMe (1) and (Ph2P)2N(p-C6H4)SMe (2), the Fe(II) complexes [FeCl2(1)]n (3), [FeCl2(2)]2 (4), [Fe(OAc)(1)2]PF6 (5), and [Fe(OAc)(2)2]PF6 (6) were synthesized and characterized by Fourier transform IR, mass spectrometry, elemental analysis, and also by X-ray diffraction for 3, 4, and 6. Complex 3 is a coordination polymer in which 1 acts as a P,P-pseudochelate and a (P,P),S-bridge, whereas 4 has a chlorido-bridged dinuclear structure in which 2 acts only as a P,P-pseudochelate. Since these complexes were obtained under strictly similar synthetic and crystallization conditions, these unexpected differences were ascribed to the different spacer between the nitrogen atom and the −SMe group. In both compounds, one Fe–P bond was found to be unusually long, and a theoretical analysis was performed to unravel the electronic or steric reasons for this difference. Density functional theory calculations were performed for a set of complexes of general formula [FeCl2(SR2){R21PN(R2)P′R23}] (R = H, Me; R1, R2, and R3 = H, Me, Ph), to understand the reasons for the significant deviation of the iron coordination sphere away from tetrahedral as well as from trigonal bipyramidal and the varying degree of unsymmetry of the two Fe–P bonds involving pseudochelating PN(R)P ligands. Electronic factors nicely explain the observed structures, and steric reasons were further ruled out by the structural analysis in the solid-state of the bis-chelated complex 6, which displays usual and equivalent Fe–P bond lengths. Magnetic susceptibility studies were performed to examine how the structural differences between 3 and 4 would affect the interactions between the iron centers, and it was concluded that 3 behaves as an isolated high-spin Fe(II) mononuclear complex, while significant intra- and intermolecular ferromagnetic interactions were evidenced for 4 at low temperatures. Complexes 3 and 4 were also tested in catalytic ethylene oligomerization but did not exhibit any significant activity under the studied conditions.

Bis(ether-functionalized NHC) Nickel(II) Complexes, Trans to Cis Isomerization Triggered by Water Coordination, and Catalytic Ethylene Oligomerization

The new nickel(II) complexes containing NHC ligands N-substituted by a CH2CH2OR ether group (R = Me or Ph) [NiCl2{ImMes(C2OMe)}2] (6), [NiCl2{Imn-Bu(C2OMe)}2] (7), [NiBr2{ImDiPP(C2OMe)}2] (8), [NiBr2{ImMes(C2OMe)}2] (9), [NiBr2{Imn-Bu(C2OMe)}2] (10), NiBr2{ImMes(C2OPh)}2] (18), [NiI2{ImDiPP(C2OMe)}2] (21), [NiI2{ImMes(C2OMe)}2] (22), and [NiI2{Imn-Bu(C2OMe)}2] (23) were synthesized in good yields and fully characterized by NMR spectroscopy and X-ray diffraction analysis. The reaction conditions were optimized and further applied to thioether or nonfunctionalized NHC ligands, affording [NiBr2{ImDiPP(C2SPh)}2] (19) and [NiBr2{ImDiPP(n-Bu)}2] (20), respectively. Equilibria involving syn/anti isomers were unveiled for complexes [NiCl2{ImDiPP(C2OMe)}2] (5), 6–10, and 18–23. Reactions of 6 and 20 with a halide abstractor afforded the dicationic aquo complexes cis-[Ni{ImMes(C2OMe)}2(H2O)2][PF6]2 (27) and cis-[Ni{ImDiPP(n-Bu)}2(H2O)2][PF6]2 (28), in which a cis arrangement of the carbene ligands is evidenced, which contrasts with that in their precursors. These molecules represent rare examples of nickel aquo NHC complexes and of complexes with two cis monodentate NHC ligands. The new complexes reported in this work (15 crystal structures) displayed moderate activities as precatalysts for ethylene oligomerization and favored dimerization.

Cationic Palladium(II) Complexes of Phosphine–Sulfonamide Ligands: Synthesis, Characterization, and Catalytic Ethylene Oligomerization

A series of cationic palladium(II) complexes bearing phosphine–sulfonamide ligands, [(P,O)PdMe(lutidine)][SbF6], were synthesized and used for catalytic ethylene oligomerization. The molecular structure of the complex {[N,N-dicyclohexyl-2-(diphenylphosphanyl)benzenesulfonamide]PdMe(lutidine)}[SbF6] shows that the phosphorus atom and the oxygen atom coordinate to the palladium center. The ethylene oligomerization behavior is greatly influenced by the phosphino substituents, while the substituents on sulfonamide show only minimal effects. Complexes containing the diphenylphosphanyl group are highly selective for ethylene dimerization, affording 1-butene exclusively with moderate activity. The bulkier bis(2-methoxyphenyl)phosphanyl group leads to higher activity and gives α-olefins containing mainly 1-butene and 1-hexene, with a 1-hexene content of up to 35%. The palladium complexes bearing alkyl phosphino substituents give 1-butene and 1-hexene as the major products; a small amount of 2-butene (<5%) was observed, suggesting the occurrence of chain walking. The addition of B(C6F5)3 greatly enhances the catalytic activity. Experimental results suggest that the increase in activity is likely due to the abstraction of lutidine, not from the coordination of B(C6F5)3 to the sulfonamide oxygen atom.

Combined Experimental and Theoretical Study of Bis(diphenylphosphino)(N-thioether)amine-Type Ligands in Nickel(II) Complexes for Catalytic Ethylene Oligomerization

Starting from the new ligands bis(diphenylphosphino)(N-4-(methylthio)phenyl)amine (4, N(PPh2)2(p-C6H4)SMe) and its monosulfide derivative (Ph2P)N{P(S)Ph2}(p-C6H4)SMe (4·S), we have prepared and characterized, including by X-ray crystallographic studies, their Ni(II) complexes [NiCl2{(Ph2P)2N(p-C6H4)SMe-P,P}] (5) and [NiCl2{(Ph2P)N{P(S)Ph2}(p-C6H4)SMe-P,S}] (6), respectively. The bis-sulfide compound N{P(S)Ph2}2(p-C6H4)SMe (4·S2) was also prepared and structurally characterized. Computational studies showed that the combined influence of stronger P donors and a four-membered-ring P,P chelate leads to complex 5 being thermodynamically more stable than 6, which contains one weaker P═S donor group but a five-membered P,P═S chelate ring. For comparison, the bis-chelate complex [Ni{(Ph2P)N{P(S)Ph2}(p-C6H4)SMe-P,S}2](BF4)2 (7), the monochelate complexes [NiBr2{(Ph2P)N{P(S)Ph2}(p-C6H4)SMe-P,S}] (8) and the Pd(II) analogue of 6, [PdCl2{(Ph2P)N{P(S)Ph2}(p-C6H4)SMe-P,S}] (9), were synthesized and structurally characterized and their solution behavior was investigated. The catalytic activity and selectivity in ethylene oligomerization of the Ni(II) complexes 5 and 6 and their known N-(methylthio)propyl analogues [NiCl2{(Ph2P)2N(CH2)3SMe-P,P}] (2) and [NiCl2{(Ph2P)N{P(S)Ph2}(CH2)3SMe-P,S}] (3), which were obtained from the bis(diphenylphosphino)(N-(methylthio)propyl)amine ligand N(PPh2)2(CH2)3SMe (1) and its monosulfide derivative (Ph2P)N{P(S)Ph2}(CH2)3SMe (1·S), respectively, revealed a significant influence of the nature of the N-substituent (aryl vs alkyl thioether) and of the chelate ring size (P,P vs P,P═S). DFT calculations showed that the trend in ΔErel, [NiCl2(P,P)] > [NiCl2(P,P═S)] > [NiCl2(P═S,P═S)], results from the stronger covalent character of the Ni–P vs Ni–S bond. Using AlEtCl2 as cocatalyst, mostly ethylene dimers were produced, with significant amounts of trimers (selectivity in the range 11–36%). Productivities up to 40400 and 48200 g of C2H4/((g of Ni) h), with corresponding TOF values of 84800 and 101100 mol of C2H4/ ((mol of Ni) h), were obtained with precatalysts 2 and 3, respectively.

Monometallic nickel(II) complexes containing N,N′-iminopyridine chelating ligands with dendritic substituents: The influence of dendrimer topology on the catalytic oligomerization and polymerization of ethylene

Iminopyridine ligands of general formula Gn-PBE-ONN (Gn-PBE=Fréchet-type dendritic wedges of generation G0 (1), G1 (2), G2 (3), and G3 (4); –ONN=-O-4-(2,5-Me2C6H2)-NCH-2-py) have been prepared starting from H-ONN. Reaction of these bidentate ligands with [NiBr2(DME)] results in the nickel(II) complexes [NiBr2(Gn-PBE-ONN)] (5–8). The methylaluminoxane (MAO)-activated monometallic complexes have been studied in the transformation of ethylene into mixtures of polyethylene and oily oligomers, and their catalytic performance scrutinized as a function of dendritic size. A comparison with the behavior observed for related polymetallic dendrimers has enabled the dendritic features that affect various catalytic parameters to be determined. Thus, it has been possible to discern whether the dendritic effect detected in the catalysis should be ascribed to the metallic nuclearity rather than the bulkiness of the metallodendrimer.

A phosphino-oxazolineligand as a P,N-bridge in palladium/cobalt or P,N-chelate in nickel complexes: catalytic ethylene oligomerization

The Pd(II) complex [PdCl(2)(1)] [1 = ({oxazolin-2-yl}methyl)diphenylphosphine] was obtained by the 1:1 reaction of 1 with [PdCl(2)(NCPh)(2)]. Although this neutral complex is stable in the solid-state and in solution, it reacts with the dinuclear complex [CoCl(2)(μ-1)](2) to afford the heterometallic zwitterionic complex [{PdCl(1)}(+)(μ-1)(CoCl(3))(-)] (2). Under inert atmosphere, two equivalents of 1 reacted with [NiCl(2)(dme)] to give trans-[NiCl(2)(1)(2)] (3) in CH(2)Cl(2) but cis-[NiCl(2)(1)(2)] (4) in CHCl(3). When the latter reaction was performed in air, trans-[NiCl(2)(5)(2)] (6) [5 = ({oxazolin-2-yl}methyl)diphenylphosphine oxide] was obtained. All metal complexes, 2, 3, 4 and 6, have been structurally characterized by X-ray diffraction. Complexes 3, 4 and 6 have been evaluated as precatalysts for ethylene oligomerisation in the presence of AlEtCl(2) as cocatalyst. Complexes 3 and 6 yielded a turnover frequency (TOF) of 60,700 and 62,600 mol of C(2)H(4)/((mol of Ni)·h), respectively, in the presence of 10 equiv. of AlEtCl(2). In the presence of only 6 equiv. of cocatalyst, these Ni complexes yielded TOF values of 41,500 and 58,000 mol of C(2)H(4)/((mol of Ni)·h), respectively.

Oligomerization of Ethylene Catalyzed by Iron and Cobalt in Organoaluminate Dialkylimidazolium Ionic Liquids

Cationic iron and cobalt acetonitrile cationic complexes were prepared and used as catalyst precursors in catalytic ethylene oligomerization. The effects of temperature and the nature and effects of the co-catalysts were evaluated. The iron and cobalt catalysts are less active, giving turnover frequencies of 20,000 to 30,000 h−1 while the corresponding nickel analogs exhibit turnover frequencies of 215,000 h−1. The iron and cobalt catalysts were more selective for the synthesis of 1-butene, especially at lower temperatures, compared to the nickel catalyst.

Syntheses, Structures, and Catalytic Ethylene Oligomerization Behaviors of Bis(phosphanyl)aminenickel(II) Complexes Containing N‐Functionalized Pendant Groups

AbstractSeveral N‐functionalized bis(phosphanyl)amine ligands respectively containing benzyl, furfuryl, thiophene‐2‐methyl, thiophene‐2‐ethyl, and 2‐picolyl groups (1a–e) were synthesized and characterized. The ligands reacted with (DME)NiBr2 in CH2Cl2 to give their corresponding nickel complexes [Ph2PN(R)PPh2NiBr2] [R = CH2C6H5 (2a), CH2C4H3O (2b), CH2C4H3S (2c), CH2C5H4N (2d), and CH2CH2C4H3S (2e)]. The structures of these complexes were established by single‐crystal X‐ray crystallography. All these nickel complexes were highly active towards ethylene oligomerization in the presence of methylaluminoxane or Et2AlCl, producing a high content of butene (C4). Especially for 2e, which contains a thiophene‐2‐ethyl pendant group, the oligomerization products obtained at –40 °C contained 95.9 mol‐% C4 fraction with 100 mol‐% 1‐butene. Over 50 °C, however, these nickel complexes underwent Friedel–Crafts alkylation of toluene with ethylene and the olefin oligomers.(© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2009)

Nickel Complexes with Phosphinito-Oxazoline Ligands: Temperature-Controlled Formation of Mono- or Dinuclear Complexes and Catalytic Oligomerization of Ethylene and Propylene

The complex [NiCl2{Ph2POCH2oxMe2}] (Ph2POCH2oxMe2 = 2-((diphenylphosphinooxy) methyl)-4,4-dimethyl-4,5-dihydrooxazole) 14 has been synthesized by reaction of solid [NiCl2(DME)] (DME = 1,2-dimethoxyethane) with a CH2Cl2 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/CH2Cl2 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 phosphino- or phosphinito-oxazoline or phosphino-thiazoline, 14a has been evaluated as precatalyst in the oligomerization of ethylene, with AlEtCl2 or MAO as cocatalyst, or propylene, with MAO as cocatalyst. With AlEtCl2 as activator (6 equiv), the catalytic activities with ethylene were generally modest and [NiCl2{Ph2PCH2ox}] (Ph2PCH2ox = 2-((diphenylphosphinooxy)methyl)-4,5-dihydrooxazole) 1 was the most active, with turnover frequencies (TOF) up to 7.9 × 104 mol of C2H4 (mol Ni × h)−1, whereas 14a, activated with 2 equiv of AlEtCl2, 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 × 104 mol of C2H4 (mol Ni × h)−1. The highest selectivity for butenes was observed with complex [NiCl2{Ph2PCH2thiazMe2}] 3. With propylene, TOFs up to 3.3 × 104 mol of C3H6 (mol Ni × h)−1 were obtained with [NiCl2{Ph2POCH2pyridine}] 8 and selectivities for C6 products higher than 98.5% were observed with precatalysts 3, [NiCl2{t-Bu2POCH2pyridine}] 9, and 14a.

Bis(diphenylphosphino)methane-Phosphonate Ligands and Their Pd(II), Ni(II) and Cu(I) Complexes. Catalytic Oligomerization of Ethylene

The bis(diphenylphosphino)methane-phosphonate-based (dppm-phosphonate) ligands (Ph(2)P)(2)CHP(O)(OR)(2) (R = Me, L(1); R = Ph, L(2)) form metal complexes by selective coordination of the diphosphine moiety to Pd(II) and Ni(II) centers. The formation of complexes containing the chelating, deprotonated form of ligand L(1) or L(2) occurred when basic ligands were present in the precursor complex, such as Me or dmba (on Pd(II)) or acac (on Ni(II)). The Cu(I) complex [CuL(1)](2)(BF(4))(2) (9) was obtained that is suggested to be dinuclear, each Cu(I) being chelated by a phosphine and a P=O donor and further bound to the phosphine group of another ligand. The crystal structures of the mononuclear complexes [PdCl(2){(Ph(2)P)(2)CHP(O)(OMe)(2)-P,P}] (2a), [PdCl(2){(Ph(2)P)(2)CHP(O)(OPh)(2)-P,P}] (2b), [Pd{(Ph(2)P)(2)CP(O)(OMe)(2)-P,P}(2)] (6a) in 6a.2CH(2)Cl(2), [Pd{(Ph(2)P)(2)CP(O)(OPh)(2)-P,P}(2)] (6b), [Ni{(Ph(2)P)(2)CP(O)(OMe)(2)-P,P}(2)] (10a) in 10a.4CHCl(3), [Ni{(Ph(2)P)(2)CP(O)(OPh)(2)-P,P}(2)] (10b) in 10b.4CHCl(3), [NiCl(2){(Ph(2)P)(2)CHP(O)(OMe)(2)-P,P}] (11a) in 11a.CHCl(3) and of the dinuclear complexes [Pd(mu-Cl){(Ph(2)P)(2)CP(O)(OMe)(2)-P,P}](2) (7a) and [Pd(mu-Cl){(Ph(2)P)(2)CP(O)(OPh)(2)-P,P}](2) (7b) have been determined by X-ray diffraction. The complexes [Ni{(Ph(2)P)(2)CC(O)NPh(2)-P,P}(2)] (13) and [Ni{Ph(2)PC(Ph)P(O)(OEt)(2)-P,O}(2)] (15) were prepared by reaction of [Ni(acac)(2)] with the known, neutral ligands (Ph(2)P)(2)CHC(O)NPh(2) and Ph(2)PCH(Ph)P(O)(OEt)(2), respectively. The Ni(II) complexes were evaluated for the catalytic oligomerization of ethylene and afforded similar results when AlEtCl(2) was used as cocatalyst. Complexes 11a,b were the most active, with a turnover frequency (TOF) of 78 300 mol of C(2)H(4)/(mol of Ni)h) for complex 11b in the presence of 10 equiv of AlEtCl(2) and showed a high selectivity for C(4) and C(6) olefins with up to 93% C(4) for 10a in the presence of 6 equiv AlEtCl(2), whereas when only 3 equiv cocatalyst was used with 10a, 64% trimers were observed. In the presence of methylalumoxane (MAO) as cocatalyst, precatalysts 10a,b, 11a,b, and 15 gave moderate TOFs, up to 11,660 mol of C(2)H(4)/(mol of Ni)h) for complex 11a with 400 equiv of MAO. Mostly ethylene dimers were formed but up to 39% trimers were observed with 10a in the presence of 400 equiv MAO.

Chromium (iii)-bis(iminophosphoranyl)methanido complexes: synthesis, X-ray crystal structures and catalytic ethylene oligomerization

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(μ-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.

Synthesis, structure, magnetic and catalytic properties of new dinuclear chromium(iii) complexes with oxazoline alcoholate ligands

The dinuclear chromium complexes [Cr(2)(N,O)(3)Cl(3)] (6) (N,O = 4,4-dimethyl-2-oxazolylmethanolate), [Cr(2)(N,O(Me2))(2)(EtOH)(2)Cl(4)] (7) and [Cr(2)(N,O(Me2))(2)(H(2)O)(2)Cl(4)] (8) (N,O(Me2) = 4,4-dimethyl-2-oxazolyldimethylmethanolate) have been prepared and characterized, including by single-crystal X-ray diffraction. Complex 6 is unsymmetrical, with two chloride ligands terminally bound to one Cr atom, whereas 7 and 8 (in 8 x C(4)H(8)O) which contain two molecules of coordinated ethanol or water, respectively, are centrosymmetric. These chromium complexes are paramagnetic, and the magnetic properties of 6 and 7 in the solid state correspond to antiferromagnetic behaviour, which was confirmed by DFT calculations of their electronic structures. Complexes 6-8 were evaluated in the catalytic oligomerization and/or polymerization of ethylene with different aluminium-based cocatalysts, and MMAO proved to be the most effective one. In the presence of MMAO, the influence of different reaction parameters, such as the Al/Cr molar ratio, reaction temperature and ethylene pressure, was investigated. Complex 7 showed the highest activity for ethylene polymerization at both 1 atm and 10 atm of ethylene pressure, up to 620 000 g mol(-1)(Cr) h(-1) in the latter case.

Nickel(II) Complexes Chelated by 2-Arylimino-6-benzoxazolylpyridine: Syntheses, Characterization, and Ethylene Oligomerization

2-(2-Benzoxazolyl)-6-(1-(arylimino)-ethyl)pyridines (L) were designed as ligands, and their nickel complexes LNiX2 (X = Cl, 1a−7a; X = Br, 1b−7b) were formed. All ligands were fully characterized by NMR, FT-IR spectra, and elemental analyses, while the nickel complexes were examined by FT-IR spectra and elemental analyses. The molecular structures of nickel complexes were established by single-crystal X-ray diffraction. Complex 6a possesses coordination number 6 by coordination of one ligand, two moles of methanol, and one chloride anion, whereas complexes 1b and 5b possess coordination number 5 with distinct distortions, for 1b toward trigonal-bipyramidal geometry and for 5b toward square-pyramidal geometry. The nickel complex 1a was evaluated in the catalytic oligomerization of ethylene with different alkylaluminums as cocatalysts, and diethylaluminum chloride (Et2AlCl) proved to be the most effective. Upon activation with Et2AlCl, all nickel complexes showed outstanding thermal stability and good catalytic activity toward ethylene dimerization with high selectivity for α-C4.

Transformation of 2-alkoxyimidate-1,10-phenanthroline metal (Mn 2+, Co 2+ and Ni 2+) chlorides from bis(2-cyano-1,10-phenanthroline) metal chlorides: Syntheses, characterizations and their catalytic behavior toward ethylene oligomerization

The 2-alkoxyimidate-1,10-phenanthroline complexes of manganese, cobalt and nickel have been synthesized by the reaction of 2-cyano-1,10-phenanthroline with metal dichloride in the corresponding alcohol. The metal complexes bearing two 2-cyano-1,10-phenanthrolines were isolated in non-protonic solvent as the coordination around metal core with two ligands and two chlorides. The alkoxyimidation of nitrile linked on ligand was speeded in forming the 2-alkoxyimidate-1,10-phenanthrolinyl metal complexes. All the complexes have been characterized by FT-IR spectra and elemental analysis, and some of their structures have also been confirmed by single-crystal X-ray diffraction analysis. All the metal complexes were evaluated in the catalytic oligomerization of ethylene with some alkylaluminums as co-catalyst; in which manganese complexes were less active, cobalt complexes showed low to moderate activities, and nickel complexes gave moderate to good activities.

Synthesis, structure, and catalytic ethylene oligomerization of nickel complexes bearing 2-pyrazolyl substituted 1,10-phenanthroline ligands

A series of nickel(II) halide complexes [NiCl 2(L)] ( 1a–12a) and [NiBr 2(L)] ( 1b–12b) bearing 2-pyrazolyl substituted 1,10-phenanthroline derivatives ( L 1 –L 12 ) have been synthesized and characterized by elemental analysis, IR spectroscopy and X-ray diffraction analysis (for 1a′, 10b and 12b). Upon activation with methylaluminoxane (MAO), these complexes display good catalytic activities in ethylene oligomerization (up to 3.01 × 10 5 g mol(Ni) −1 h −1 at 10 atm of ethylene for 12a with L 12 = 2-(3,5- diphenylpyrazol-1-yl)-9- mesityl-1,10-phenanthroline). Complexes with bulkier aryl groups in the 9-position of the phenanthroline ring and the 3- and 5-position of the pyrazolyl ring give higher activities. This is explained with the formation of a more directional environment, a reaction channel around the nickel center which enhances the probability of insertion over dissociation after ethylene coordination to Ni. Also, bulkier aryl substituents can suppress chain-transfer reactions (typically β-H elimination) and therefore increase the activity.

Synthesis, structure, and catalytic ethylene oligomerization of nickel(II) and cobalt(II) complexes with symmetrical and unsymmetrical 2,9-diaryl-1,10-phenanthroline ligands

A series of nickel(II) and cobalt(II) complexes, NiX 2L (X = Cl, Br; 1– 6) and CoCl 2L ( 7– 9), with 2,9-diaryl-1,10-phenanthroline ligands ( L 1– L 3) have been synthesized and characterized by elemental analysis, UV–Vis, IR spectroscopy, and X-ray crystal structural study (for 1, 4– 7, 9). The solid-state structures of 1, 5– 7 and 9 show four-coordinate, slightly flattened tetrahedral geometry at the Ni(II) or Co(II) center, while 4 is five-coordinated (square-pyramidal), containing a THF molecule as an auxiliary ligand. The title complexes ( 1– 9) display good catalytic activities in ethylene oligomerization when activated with methylaluminoxane (MAO). While the Co(II) precatalysts produce primarily C 4 isomers, the Ni(II) complexes give ethylene dimers and trimers at normal pressure. The activities and yields of linear α-olefins increase with increasing ethylene pressure for the Ni(II) complexes, leading to more high-molar-mass products (C 8–C 18). Complex 6 displays the best catalytic activity among the complexes studied (up to 1518 kg/mol[Ni] h at 10 atm).

Nickel and iron complexes with N,P,N-type ligands: synthesis, structure and catalytic oligomerization of ethylene

The N,P,N-type ligands bis(2-picolyl)phenylphosphine (), bis(4,5-dihydro-2-oxazolylmethyl)phenylphosphine (), bis(4,4-dimethyl-2-oxazolylmethyl)phenylphosphine () and bis(2-picolyloxy)phenylphosphine () were used to synthesize the corresponding pentacoordinated Ni(ii) complexes [Ni{bis(2-picolyl)phenylphosphine}Cl(2)] (), [Ni{bis(4,5-dihydro-2-oxazolylmethyl)phenylphosphine}Cl(2)] (), [Ni{bis(4,4-dimethyl-2-oxazolylmethyl)phenylphosphine}Cl(2)] () and [Ni{bis(2-picolyloxy)phenylphosphine}Cl(2)] (), respectively. The hexacoordinated iron complexes [Fe{bis(2-picolyl)phenylphosphine}(2)][Cl(3)FeOFeCl(3)] (), [Fe{bis(4,5-dihydro-2-oxazolylmethyl)phenylphosphine}(2)][Cl(3)FeOFeCl(3)] () and the tetracoordinated complex [Fe{bis(4,4-dimethyl-2-oxazolylmethyl)phenylphosphine}Cl(2)] (abbreviated [FeCl(2)(NPN(Me2)-N,N)]) were prepared by reaction of FeCl(2).4H(2)O with ligands , respectively. The crystal structures of the octahedral complexes and , determined by X-ray diffraction, showed that two tridentate ligands are facially coordinated to the metal centre with a cis-arrangement of the P atoms and the dianion (mu-oxo)bis[trichloroferrate(iii)] compensates the doubly positive charge of the complex. The cyclic voltammograms of and showed two reversible redox couples attributed to the reduction of the dianion (Fe(2)OCl(6))(2-) (-0.24 V for and -0.20 V for vs. SCE) and to the oxidation of the Fe(ii) ion of the complex (0.67 V for and 0.52 V for vs. SCE). The cyclic voltammogram of [FeCl(2)(NPN(Me2)-N,N)] showed a reversible redox couple at -0.17 V vs. SCE assigned to the oxidation of the Fe(ii) atom and an irreversible process at 0.65 V. The complexes , and [FeCl(2)(NPN(Me2)-N,N)] have been evaluated in the catalytic oligomerization of ethylene with AlEtCl(2) or MAO as cocatalyst. The nickel complex proved to be the most active precatalyst in the series, with a turnover frequency (TOF) of 61 800 mol(C(2)H(4)) mol(Ni)(-1) h(-1) with 10 equiv. of AlEtCl(2) and 12 200 mol(C(2)H(4)) mol(Ni)(-1) h(-1) with 200 equiv. of MAO. Precatalysts and were the most selective in butenes, up to 90% with 6 equiv. of AlEtCl(2) and 89% with 2 equiv. of AlEtCl(2), respectively, and up to 92% butenes with 400 equiv. of MAO and 91% butenes with 200 equiv. MAO, respectively. The best selectivities for 1-butene were provided by and AlEtCl(2) (up to 31% with 6 equiv.) and with MAO (up to 72% with 200 equiv.). The iron complexes were not significantly active with AlEtCl(2) or MAO as cocatalyst.

Synthesis of nickel complexes with bidentate N,O-type ligands and application in the catalytic oligomerization of ethylene

The dinuclear complexes [Ni(micro-Cl){(4,5-dihydro-4,4-dimethyloxazol-2-yl)methanol}](2)Cl(2) and [Ni(micro-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.

SHOP-type nickel complexes with alkyl substituents on phosphorus, synthesis and catalyticethylene oligomerization

The beta-keto phosphorus ylides (n-Bu)3P=CHC(O)Ph 6, (t-Bu)2PhP=CHC(O)Ph 7, (t-Bu)Ph2P=CHC(O)Ph 8, (n-Bu)2PhP=CHC(O)Ph 9, (n-Bu)Ph2P=CHC(O)Ph 10, Me2PhP=CHC(O)Ph 11 and Ph3P=CHC(O)(o-OMe-C6H4) 12 have been synthesized in 80-96% yields. The Ni(II) complexes [NiPh{Ph2PCH...C(...O)(o-OMeC6H4)}(PPh3)] 13, [NiPh{Ph(t-Bu)PCHC(O)Ph}(PPh3)] 15, [NiPh{(n-Bu)2PCH...C(...O)Ph}(PPh3)] 16 and [NiPh{Ph(n-Bu)PCH...C(...O)Ph}(PPh3)] 17 have been prepared by reaction of equimolar amounts of [Ni(COD)2] and PPh3 with the beta-keto phosphorus ylides 12 or 8-10, respectively, and characterized by 1H and 31P{1H} NMR spectroscopy. NMR studies and the crystal structure determination of 13 indicated an interaction between the hydrogen atom of the C-H group alpha to phosphorus and the ether function. The complexes [NiPh{Ph2PCHC(O)Ph}(Py)] 18, [NiPh{Ph(t-Bu)PCHC(O)Ph}(Py)] 19, [NiPh{(n-Bu)2PCH...C(...O)Ph}(Py)] 20, [NiPh{Ph(n-Bu)PCH...C(...O)Ph}(Py)] 21 and [NiPh{Me2PCH...C(...O)Ph}(Py)] 22 have been isolated from the reactions of [Ni(COD)2] and an excess of pyridine with the -keto phosphorus ylides Ph3PCH=C(O)Ph 3 or 8-11, respectively, and characterized by 1H and 31P{1H} NMR spectroscopy. Ligands 3, 8, 10 and 12 have been used to prepare in situ oligomerization catalysts by reaction with one equiv. of [Ni(COD)2] and PPh3 under an ethylene pressure of 30 or 60 bar. The catalyst prepared in situ from 12, [Ni(COD)2] and PPh3 was the most active of the series with a TON of 12700 mol C2H4 (mol Ni)-1 under 30 bar ethylene. When the beta-keto phosphorus ylide 8 was reacted in situ with three equiv. of [Ni(COD)2] and one equiv. of PPh3 under 30 bar of ethylene, ethylene polymerization was observed with a TON of 5500 mol C2H4 (mol Ni)-1.