Toluene nickel complex

Nickel complexes are also active catalyst for the isomerization of allylic alcohols. Ni(dppb)2, prepared by mixing Ni(cod)2/2dppb (2equiv.), catalyzed the isomerization of geraniol to citronellal in the presence of CF3C02H (4equiv.) in toluene at 80 °C (Equation (10)).34... 

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%. 

Several (bis)carbene nickel complexes were tested as catalysts for the dimerisation of propene or 1-butene (Scheme 8.3). IS While the activity of these complexes was very poor in the dimerisation of 1-butene when toluene was used as solvent, turnover frequencies as high as 7,000 mol mol h 1 were observed at ambient temperature with C4Ciim]Cl-AlCL-iV-methylpyrrole (0.45 0.55 0.10) as solvent. With propene as substrate, TOFs of 75,000 mol-moL -lf1 were achieved. Compared to NiCl2(PCy3)2, the activity of the carbene complexes is considerably higher, but selectivity towards the desired, highly branched propene dimer is low. 

A similar, but bimolecular, photoinduced reaction was observed on the basis of the nickel complex (28), p-toluene thiolate, and thioanisole reactants to generate methane and disulfide. The thiyl radical and Ni(I) complex was prepared by the photolysis of the Ni(II) complex (28) and j -toluene-thiolate anion in acetonitrile solution. Upon irradiation (A, = 350 nm) of the mixture of complex (28), j -toluene-thiolate ion, and thioanisole in acetonitrile under argon, gas chromatography-mass spectral analysis showed the formation of methane, ditolyl disulfide (TolS)2, and a mixed disulfide TolSSPh. The proposed catalytic mechanism is depicted in... 

Oxidative fluorination of toluene derivatives to the corresponding fluoromethylben-zenes is possible using appropriate lead or nickel complexes in liquid hydrogen fluoride, but fluorination becomes more difficult as the reaction progresses because fluorine substituents increase the oxidation potential of the substrate [146] (Figure 3.20). Consequently, it seems unlikely that the ECF process (Chapter 2, Section III) could proceed to perfluorination by an analogous mechanism. 

Catalytic Enantioselective Conjugate Addition of Dialkylzincs to Enones. A chiral nickel complex modified with DBNE and an achiral ligand such as 2,2 -bipyridyl in acetonitrile/toluene is an highly enantioselective catalyst for the addition of dialkylzincs to enones. p-Substituted ketones with up to 90% ee are obtained (eq 23). The method is the first highly enantioselective catalytic conjugate addition of an oiganometallic reagent to an enone. 

In the case of tetramethylbutatriene, Ni(0) catalyzes not only the cyclodimerization (formation of [4]radialene 94), but also the cyclotrimerization, leading to [6]radialene 95 and its isomer 96 (see also Section ILD). The product pattern depends to some extent on the nature of the catalyst, but the choice of solvent seems to be more crucial. This is illustrated impressively by the Ni(cod)2-catalyzed reaction of 93, which leads exclusively to the [4]radialene in toluene solution, but to the [6]radialene in DMF. Interestingly, the stoichiometric reaction between 93 and (2,2Tbipyridyl)-(l,5-cyclooctadiene)nickel yields the nickel complex 97, which has been isolated and characterized by X-ray diffraction. On treatment of 97 with two equivalents of maleic anhydride, reductive elimination of nickel takes place and octamethyl[4]radialene (94) is formed in good yield. This reaction sequence sheds light on the mechanism of the Ni-catalyzed reactions mentioned above further ideas on the mechanism of the cyclodimerization and cyclotrimerization reactions have been developed by lyoda and coworkers. ... 

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... 

Palladium belongs to the group 10 elements, and as with nickel, it forms stable Pd(0) and Pd(II) complexes. The use of such complexes (Pd-1 and Pd-2) has been reported for the polymerization of MMA with CCI4 initiator in toluene at 70 °C.137 The activity is moderate (conversion 70—80% in 24 h), similar to that of the nickel complexes. The Mn increased in direct proportion to monomer conversion, while the MWD was broader (MJMn 1.8). In contrast, polymerizations of styrene and acrylates were not controlled with Pd catalysts. 

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. 

Our search for a more active system led us to bis(pentafluorophenyl)nickel complexes originally reported by Klabunde and co-workers in the 1980s [56]. One of the more interesting complexes reported was (// -toluene)Ni(C6F5)2 (Fig. 4.26). Toluene can be readily replaced by a number of neutral electron donors including xylene, mesitylene, THF, PEtj, and norbornadiene. In fact, Klabunde noted that formation of (norbornadiene)Ni(C6F5)2 was accompanied by intractable polymer. Klabunde speculated that vinyl addition polymerization occurred with possible crosslinking. Unfortunately, the insolubility of the norbornadiene polymer prevented further analysis. 

Thus, we synthesized and tested this toluene complex and found that it does indeed effect the polymerization of norbornene-type monomers. Polymerization of norbornene-type monomers is not restricted to nickel complexes containing CgFs ligands. We have found that the electron-withdrawing tris(2,4,6-trifluoromefhyl-phenyl) ligand [57] is also quite effective in polymerizing both norbornene and 5-triethoxysilylnorbornene, for example. At a 4000 1 monomer to nickel ratio, Ni[2,4,6-tris(trifluoromethyl)phenyl]2(l,2-dimethoxyethane) (Fig. 4.27) gave 37% conversion into polymer from an 80 20 norbornene 5-triethoxysilylnorbornene monomer mixture. 

Typical examples of the stabilizers generally used to prevent the above chain reaction are (a) UV absorbers — 2(2-hydroxy-3-tert-butyl-5-methylpheny l)-5-c hi or ob en zo tr ia zo le and 2-h yd ro xy-4-octoxybenzophenone (b) Antioxidants — 3,5-di-tert-butyl-4-hydroxy-toluene and octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propa-noate (c) Peroxide decomposers — dilauryl thiodipropionate. In addition quenchers such as the organic nickel complex, Ni(II) bis-(diisopropyl dithiocarbamate) are used for the deactivation of the excited states of the chromophoric groups responsible for light initiation. 

Rearrangement. Effective catalysis of the vinylcyclopropane-to-cyclopentene rearrangement by a nickel complex in refluxing toluene renders siloxycyclopentenes readily available. 

A nickel complex fixed to polystyrene by means of Ni-C through oxidative addition of halogenated polystyrene to Ni(0)-tetra(triphenylphos-phine) [261]. The catalyst was synthesized to an approximate degree of polymerization of 1100 in toluene solution at room temperature in the presence of nitrogen. It was found that the obtained complex was highly active during C2H4-dimerization reactions conducted in the presence of catalyst-toluene suspensions as well as in the gas-solid phase. It was shown that the solvent affects catalyst selectivity. Selectivity was lower in the gas-solid system, and considerable quantities of hexenes and octenes were formed. 

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