Nickel complexes polymerization reactions

In the reaction of Ni(CNBu )4 and methyl iodide oligomerization of the isocyanide was observed the only isolable nickel complex was (I), shown below. This product is believed to arise through sequential insertions of three isocyanides into a nickel-carbon bond. Upon further treatment with additional isocyanide at a temperature greater than 60° C one obtains a polymer (RNC) presumably through multiple isocyanide insertion reactions. The addition of benzoyl chloride to Ni(CNBu )4 gave two isolable compounds Ni(CNBu )3(COPh)Cl (74%) and (II) (8.2%). This latter reaction, and the isolation of (II) in particular, suggests that the proposed mechanism for polymerization of isocyanides is reasonable. 

Mention was made earlier about insertion reactions into nickel alkyl bonds 108, 164), and about polymerizations of oleiins by isocyanide nickel complexes 31,174). 

Several combinatorial approaches to the discovery of transition metal based catalysts for olefin polymerization have been described. In one study Brookhart-type polymer-bound Ni- and Pd-(l,2-diimine) complexes were prepared and used in ethylene polymerization (Scheme 3).60,61 A resin-bound diketone was condensed with 48 commercially available aminoarenes having different steric properties. The library was then split into 48 nickel and 48 palladium complexes by reaction with [NiBr2(dme)] and [PdClMe(COD)], respectively, all 96 pre-catalysts being spatially addressable. 

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. 

Into a Schlenk tube was placed Auf 1,5-cyclooctadiene)-nickeI(0) (2.6 mmol), 2,2 -bipyridyl (2.6mmol), 1,5-cyclooctadiene (0.2ml), DMF (4ml), and toluene (8 ml). The reaction mixture was heated to 80°C for 0.5 h under argon. The dibromide comonomers 623 and 634 dissolved in degassed toluene (8 ml molar ratio of dibromides to nickel complex 0.65) were added under argon to the DMF-toluene solution and the polymerization maintained at 80°C for 3 days in the dark. 2-Bromofluorene (molar ratio of dibromides to monobromide 0.1) dissolved in degassed toluene (1ml) was added and the reaction continued for 12 h. The polymers were precipitated by addition of the hot solution dropwise to an equivolume mixture of concentrated HC1, methanol, and acetone. The isolated polymers were then dissolved in toluene or dichlor-omethane and reprecipitated with methanol/acetone (1 1). The copolymers were dried at 80°C in vacuo. The isolated yields of copolymers 240a-c were 79-85%. 

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 ability of nickel complexes, e.g., nickel carbonyl and its phosphine derivatives, to catalyze polymerization and other reactions of olefins and acetylenes has been studied extensively (46, 53), particularly by Reppe. 

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. 

The remaining polymerization route involves zero-valent nickel complexes and dihalide monomers. Variations of this route most often arise where different sources or regeneration methods of the active nickel species are utilized [82,199, 200-204]. A typical example is shown below in Scheme 51 in which poly(3-phe-nylthiophene) 50 is synthesized from the parent 2,5-dichlorothiophene. As with the Ullmann reaction, polymerization appears to be most compatible with ring systems containing electron-withdrawing substituents. 

The adoption of reaction models available for the polymerization of conjugated dienes by Ni- and Ti-catalysts to the polymerization of BD by Nd catalysis is justified by the similarities of the respective metal carbon bonds. In each of these mechanistic models the last inserted monomer is bound to the metal in a 3-allyl mode. The existence of Ni- -allyl-moieties was demonstrated by the reaction of the deuterated nickel complex [ rf- C4D6H)NiI]2 with deuter-ated BD (deuterated in the 1- and 4-position). After each monomer insertion a new 3-allyl-bond is formed [629]. As TT-allyl-complexes are known for Ti and Ni this knowledge has been adopted for Nd-based polymerization catalysts [288,289,293,308,309,630-636,638-645]. 

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... 

A phosphine-based nickel(II) bromide complex (Ni-2) also induces living radical polymerization of MMA specifically when coupled with a bromide initiator in the presence of Al(0-i-Pr)3 as an additive in toluene at 60 and 80 °C.133 The reaction rates and the effects of radical inhibitors are similar to those with Ni-1, whereas chloride initiators are not effective in reaction control. Additives are not necessary when the polymerization is carried out in the bulk or at high concentrations of monomer, either methacrylate or /v-butyl acrylate (nBA).134 An alkylphosphine complex (Ni-3) is thermally more stable and can be employed for MMA, MA, and nBA in a wide range of temperatures (60—120 °C) without additives.135 A fast polymerization proceeds at 120 °C to reach 90% conversion in 2.5 h. A zerovalent nickel complex (Ni-4) is another class of catalyst for living radical polymerization of MMA in conjunction with a bromide initiator and Al(0-i-Pr)3 to afford polymers with narrow MWDs MJMn = 1.2—1.4) and controlled molecular weights.136 The Ni(0) activity is similar to that of Ni(II) complexes whereas the controllability... 

A more product-like intermediate for the nickel-catalyzed polymerization was isolated in the reaction of the tetrakis(tert-butyl isocyanide)nickel(O) complex 10 with organic halides [14, 20] (Scheme 12). In the reaction of 10... 

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. 

Polymerizations with nickel salicylaldimine complexes 87-101 were performed in a 1 L steel autoclave at 40 bar and 30 °C. The nickel complexes (0.09 mmol) were activated with equimolar amounts of Ni(COD)2 in toluene solutions for 30 min after which the autoclave was pressurized with ethene. The reaction was terminated after 1.5 h by venting the ethene and the formed polymer powder was isolated. Details are summarized in Tab. 3.9. For comparison, complex 134, a nickel salicylaldimine complex with a 2,6-(diisopropyl)phenyl imine substituent, was screened under the same conditions. 

Thus, we discovered the unusual activation of nickel toward the polymerization of norbornene-type monomers by CgFs transfer from B(C6F5)3 to nickel [58], a reaction pathway that is typically a decomposition route for transition metal catalysts [59]. This discovery led to the development of a class of neutral, single-site nickel complexes containing electron-withdrawing group such as CgFs that are effective for the polymerization of norbornene-type monomers. 

The next attempt at these reactions were carried out by Yamamoto et al. [26], They coupled 2,7-dibromo-9,10-dihydrophenanthrene to give an ethano-bridged poly(p-phenylene) derivative [poly(9,10-dihydrophenanthrene-2,7-diyl)] (9) by way of low-valent nickel complexes, which were used either stoichiometrically as reagent (Ni(COD)2) or were generated electrochemically in the reaction mixture. As a result of the insufficient solubilization of the ethano substituents only the oligomer fraction with Mn<1000 is soluble, the polymeric products precipitating out as an insoluble powder. The value of for the soluble fraction of 9 is about 360 nm. 

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