Nickel polymerization reactions

Nickel and palladium react with a number of olefins other than ethylene, to afford a wide range of binary complexes. With styrene (11), Ni atoms react at 77 K to form tris(styrene)Ni(0), a red-brown solid that decomposes at -20 °C. The ability of nickel atoms to coordinate three olefins with a bulky phenyl substituent illustrates that the steric and electronic effects (54,141) responsible for the stability of a tris (planar) coordination are not sufficiently great to preclude formation of a tris complex rather than a bis (olefin) species as the highest-stoichiometry complex. In contrast to the nickel-atom reaction, chromium atoms react (11) with styrene, to form both polystyrene and an intractable material in which chromium is bonded to polystyrene. It would be interesting to ascertain whether such a polymeric material might have any catal3dic activity, in view of the current interest in polymer-sup-ported catalysts (51). 

Polymerization reactions of olefins and dienes cannot be treated here in detail. Knowledge of the early steps which occur on nickel, as in oligomerization reactions, help explain the course of polymerization reactions and particularly their stereospecific character, as in Ziegler-Natta polymerization. 

Nickel is frequently used in industrial homogeneous catalysis. Many carbon-carbon bond-formation reactions can be carried out with high selectivity when catalyzed by organonickel complexes. Such reactions include linear and cyclic oligomerization and polymerization reactions of monoenes and dienes, and hydrocyanation reactions [1], Many of the complexes that are active catalysts for oligomerization and isomerization reactions are supposed also to be active as hydrogenation catalysts. 

The patent literature contains several references to the use of sulfoxide complexes, usually generated in situ, as catalyst precursors in oligomerization and polymerization reactions. Thus, a system based upon bis(acrylonitrile)nickel(0> with added Me2SO or EtgSO is an effective cyclotrimerization catalyst for the conversion of butadiene to cyclo-1,5,-9-dodecatriene (44). A similar system based on titanium has also been reported (407). Nickel(II) sulfoxide complexes, again generated in situ, have been patented as catalyst precursors for the dimerization of pro-pene (151) and the higher olefins (152) in the presence of added alkyl aluminum compounds. 

The application of perfluorous polyethers in biphasic catalysis was first described by Vogt (133), who also synthesized ligands based on hexafluor-opropene oxide oligomers to create metal complexes that are soluble in the perfluorous polyethers. The solvophobic properties of the fluorous solvent were successfully incorporated in the metal complexes catalytic oligomerization and polymerization reactions with nickel and cobalt complexes were demonstrated. 

GIXD studies have demonstrated that racemic N -alkanoyl-lysincs and their corresponding AP-carboxyanhydrides, for example N, -slearoyl-lysinc-NCA, undergo spontaneous segregation of the enantiomers into enantiomorphous 2-D crystalline domains at the surface of water [194], Polymerization reactions within such enantiomorphous crystallites, using nickel acetate as... 

The nickel(II)-catalyzed polymerization of isocyanides proceeds relatively fast, a remarkable observation given the steric crowding that is introduced upon formation of the polymer chain. The driving force for the reaction is the conversion of a formally divalent carbon in the monomer into a tetravalent carbon in the polymer, yielding a heat of polymerization of 81.4 kJ moD1.169 For this polymerization reaction, a merry-go-round mechanism has been proposed. Upon mixing of the isocyanides with the Ni(II) catalyst, a square-planar complex is formed (Scheme 7), which in some occasions can be isolated when bulky isocyanides are used. Subsequent attack by a nucleophile on one of the isocyanide ligands is... 

Moreover, semi-ladder polymers based on DIC units were obtained in much more classical ways. 2,11- and 3,10-dichloro DIC derivatives were polymerized through a nickel(0)-mediated Yamamoto polymerization reaction [95]. The resulting polymers are soluble in ODCB and partially soluble in CB. The absorption maxima of the BIC-based polymers clearly indicate a planar structure. The absorption maxima of the polymeric precursors show a primary maximum around 350 nm compared to the ladder-type polymers where the maximum is centered around 470 nm [50]. This significant red shift clearly indicates the higher degree of conjugation in the planar rigid polymers. The fluorescence spectra of those polymers also show the same trend. 

The general catalytic performance of these metal complexes in polymerization of olefins was screened by the following standard procedure The complexes (50 or 100 pmol) were activated with 100 mole equivalents of methylalumoxane (MAO) in toluene solution. The polymerization reaction was carried out at a temperature of 30°C, during which ethene was added with a flow of 40 L h"t After 4.5 h, the mixture was quenched with methanol, the solid polymer isolated, washed and dried. For benchmarking a nickel diimine complex [12a] with 2,6-(di-isopropyl) phenyl substituents at the imine nitrogen atoms (133) was also included. Tab. 3.2 shows the activity and polymer data. 

All experiments were conducted at room temperature for 1 h. In run number 1, the catalyst was a mixture of Ni(dpm)2, Al Hl, and l (fl,l r) 5 in a 4000 1 10 9 norbornene Ni Al B molar ratio. High conversion (97%) and activity was achieved. In fact, fhe activity observed is in all hkelihood much higher than the calculated 373.00 g of polymer obtained per mol nickel metal per hour, since the polymerization reaction formed a puck within one minute of addition of fhe catalyst components and polymerization conversion was determined only after an hour. The molecular weight of fhe polymer obtained is extremely high, but fhe actual molecular weight data should be viewed wifh some skepticism since fhe sample was not completely soluble in trichlorobenzene at 135 °C and was partially excluded from the GPC column. 

V(L)Cl2(TpMs )] (L = N Bu L = O) were in situ supported onto SiC>2 and onto MAO and trimethylaluminum. All catalyst systems were shown to be active in ethylene polymerization. The systems were stable at different [A1]/[V] molar ratios and polymerization temperatures.21 Branched polyethylene/high-density polyethylene blends were prepared using the combined [NiChfa-diimine)] and V(T(Tp-vls )(N Bu) catalysts. The polymerization reactions were performed in hexane or toluene at three different polymerization temperatures (CPC, 30°C and 50°C) and several nickel molar fractions, using MAO as cocatalyst.22 TpMs- and TpMs -imido vanadium (V) were immobilized onto a series of inorganic supports All the systems were shown to be active in ethylene polymerization in the presence of MAO or TiBA/MAO mixture.23... 

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