Oligomerization of styrenes mediated by cationic allyl nickel complexes containing triphenylstibine or triphenylarsine (original) (raw)
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Dalton transactions (Cambridge, England : 2003), 2007
The complexes [Ni(g 3 -CH 2 CHCH 2 )Br(j 1 P-PR 2 CH 2 CH=CH 2 )] (R = Ph 1, i Pr 2) and [Ni(g 3 -CH 2 C(R )CH 2 )(j 1 P-PR 2 CH 2 CH=CH 2 ) 2 ][BAr 4 ] (R = H, R = Ph 4a, R = i Pr 4b; R = CH 3 , R = Ph 5a, R = i Pr 5b; Ar = 3,5-C 6 H 3 (CF 3 ) 2 ) have been prepared and characterized. The X-ray crystal structures of 1, 2 and 5b have been determined. 4a-b and 5a-b are catalyst precursors for the oligomerization of RC 6 H 4 CH=CH 2 to oligostyrene (R = H) or oligo(4-methylstyrene) (R = CH 3 ) respectively, without the need of a co-catalyst such as methylalumoxane. The catalytic activities range from moderate to high. The oligomerization reactions are carried out in the temperature interval 25-40 • C in 1,2-dichloroethane, using an olefin/catalyst ratio equal to 200, yielding oligostyrenes with a high isotactic fraction content P m , with M n in the range 700-1900 Dalton, and polydispersities between 1.22 and 1.64. The cationic complexes 4a-b and 5a-b are also effective catalyst precursors for the hydrosilylation reactions of styrene or 4-methylstyrene with PhSiH 3 in 1,2-dichloroethane at 40 • C using an olefin/catalyst ratio equal to 100, leading selectively to RC 6 H 4 CH(SiH 2 Ph)CH 3 (R = H, CH 3 ) in 50-79% yield.
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.
European Journal of Inorganic Chemistry, 2018
A series of new cationic R n-substituted-indenyl nickel(II) complexes containing arsine or stibine ligands were synthesized in moderate to very high yields by the protonation of the corresponding bisindenyl nickel derivatives [Ni(η-R n-Ind) 2 ] with HBF 4 , in the presence of 2 equivalents of AsPh 3 or SbPh 3 donor ligands. These complexes, with the general formula [Ni(η-R n-Ind)(EPh 3) 2 ]BF 4 (E= As, Sb), were structurally characterized by NMR and X-ray diffraction, and subsequently tested as singlecomponent catalysts for the oligomerization of styrene, leading to the formation of very low molecular weight head-to-tail oligomers (typically consisting of dimers, trimers and tetramers). The new 1-or 2monosubstituted-indenyl Ni(II) catalyst precursors exhibit extremely high catalytic activities, considerably higher than those observed for the symmetrical unsubstituted-and the 1,3-disubstitutedindenyl nickel analogues (i.e. monosubstituted >> non-substituted > 1,3-disubstituted), their reactivity pattern showing similarities with that of the corresponding allyl derivatives. A simpler and more straightforward experimental procedure for the high yield preparation of [NiBr 2 (DME)], an important nickel starting material, which was used in the preparation of the bisindenyl nickel precursors of this work, is also described. 5- 3 indenyl-ring slippage, enabling the existence of an additional coordination position and the stabilization of reaction intermediates. The process is designated by the indenyl effect, [6] being this 5- 3 haptotropic shift facilitated by the presence of the fused benzene fragment in the -Ind ring. [7] As a
Organometallics, 2009
Bidentate pyridine-phosphine ligands 1 of general structure 2-aryl-6-[2-(diphenylphosphino)ethyl]pyridine were developed, in which the aryl group is phenyl (a), 1naphthyl (b), 9-phenanthryl (c), 9-anthracyl (d), and ferrocenyl (e). The influence of these substituents on the nickel and palladium complexes of the ligands and their ethene oligomerization behavior was studied. The largest influence was observed in species with a square planar surrounded metal center; whereas the nickel dichloride complexes 5 appeared as monometallic species with a tetrahedrally surrounded metal center, a classical binding mode of the ligand was not possible for the methylpalladium chloride complexes coordinated in a square planar fashion. Instead, dinuclear species in which two ligands span two metal centers were observed for 6a-d and an undefined mixture of complexes was obtained for 6e. In contrast to these neutral palladium complexes, the cationic methylpalladium complexes 7, lacking the chloride anion, appear as well defined, monomeric complexes. When the nickel complexes 5a-d were activated with MAO, they catalyzed the oligomerization of ethene with a maximum turnover frequency of 11•10 3 mol ethene per mol nickel per hour, whereas 5e showed no activity. Selectivities for butenes were between 93 and 97 mole percent, with a maximum 1-butene content of 93%. The catalytic behavior is different from that of the nickel complex lacking an aromatic group at the ligand, again showing the influence of these substituents. The palladium complexes 7 were hardly active in ethene oligomerization, giving very small amounts of oligomers.
Styrene polymerization using nickel(II) complexes as catalysts
European Polymer Journal, 2005
Styrene polymerization is investigated with neutral and cationic Ni(II) complexes, i.e. Ni(bipy)Me 2 , 1, Ni(bipy)Br 2 , 2, Ni(phen)Br 2 , 3, or Ni(Me 2 phen)Br 2 , 4, Ni(acac) 2 , 5, (bipy = 2,2 0 -bipyridine, phen = phenanthroline, Me 2 phen = 2,9dimethyl-1,10-phenanthroline, acac = acetylacetonate), activated by [NHMe 2 Ph][B(C 6 F 5 ) 4 ] or B(C 6 F 5 ) 3 as cocatalysts, in the presence of AlMe 3 . The influence on the polystyrene features and the reaction kinetics of the nickel complex and boron activator, the Al/Ni or B/Ni molar ratios as well as the monomer concentration are studied. Catalytic systems derived from 2, 3 or 5 and [NHMe 2 Ph][B(C 6 F 5 ) 4 ] at a Ni:B:Al ratio of 1:1:5 are the most efficient at room temperature.
A catalytic and DFT study of selective ethylene oligomerization by nickel(II) oxime-based complexes
Journal of Molecular Catalysis A: Chemical, 2013
The reactivity of nickel(II) thiophenealdoxime complex (3) toward oligomerization of ethylene in the presence of an alkylaluminum co-catalyst has been studied. The complex was found to be a selective ethylene dimerization catalyst in the presence of co-catalysts such as methylalumoxane (MAO) and diethylaluminum chloride (DEAC). With DEAC, the productivity was considerably higher than with MAO. Under optimum conditions the productivity reaches 388 kg/mol catalyst/h/bar with DEAC whereas for MAO this value was 119 kg/mol catalyst/h/bar. Complex 3 displays good ethylene conversions of up to a maximum of 90% with exceptionally high ␣-selectivity for 1-butene (>99.5%) amongst C 4 products. Computational studies using density functional theory (DFT) were also carried out to ascertain the decomposition pathway for 3 as well as that for Ni(II) complex of the pyridine ketoxime ligand 2. The results suggest that loss of one of the two bidentate oxime ligands attached to the metal center through reaction with DEAC is likely for both 2 and 3. Further, calculations indicate that the subsequent decomposition step was significantly more probable for 3 than for 2 thus explaining why the pyridine ketoxime ligand bound nickel complex 2 was experimentally found to be more stable than the thiophene aldoxime bound nickel complex 3. Calculations also show that the proton of the-OH group (oxime) plays a major role in the stability of the molecules. This was confirmed experimentally by synthesizing the Ni(II) dichloro complex of Pyridine-2-carbaldehyde O-methyloxime 5 and reacting it with ethylene under similar conditions. 5 was found to be highly active even at low co-catalyst concentrations.
Macromolecules, 1996
The influence of several phosphorus(III) ligands upon the activity and the stereoregulation ability of the soluble organometallic complex [Ni(η 3 -(2-methylallyl))(η 4 -COD)]PF6 (COD ) 1,5-cyclooctadiene), 1, is studied. There is a general increase of the catalytic activity which can be associated with the P(III) ligand's lability. A detailed analysis of the mass distribution and microstructure is carried out by GPC and 1 H and 13 C NMR of the solvent-fractionated polymers. In the majority of cases, regioregular low molecular weight polymers with the structure PhCHdCH2[CH(Ph)CH2]nCH(Ph)CH3 are obtained. The addition of bulky phosphines, such as P(o-Tol)3 (o-Tol ) o-tolyl) and PCy3 (Cy ) cyclohexyl), affords highly isotactic oligomers (≈90%). For the latter, the regioselectivity of the chain growth is broken during the insertion of the last monomer, which results in the formation of a tail-to-tail end group, CH2dC-(C6H5)CH(C6H5)CH2-. The superimposed effects of η 3 -coordination of the chain end and the large stereochemical influence of these ligands seem to be the reason for the observed isospecifity.