Nickel complexes, epoxidation reactions

Macrocycle Vila readily forms the doubly deprotonated nickel complex upon addition of Ni(OAc)2. The methylene chloride soluble complex was unreactive under reaction conditions similar to those employed in the nickel cyclam/PhIO system. However, oxidation of - 8-methylstyrene occurred readily when the hypochlorite phase transfer conditions were used. Epoxidation represented about 50% of the reaction pathway with the remainder yielding a mixture of benzaldehyde and other over-oxidation products. 

Equations 1 to 3 show some of fixation reactions of carbon dioxide. Equations la and lb present coupling reactions of CO2 with diene, triene, and alkyne affording lactone and similar molecules [2], in a process catalyzed by low valent transition metal compounds such as nickel(O) and palladium(O) complexes. Another interesting CO2 fixation reaction is copolymerization of CO2 and epoxide yielding polycarbonate (equation 2). This reaction is catalyzed by aluminum porphyrin and zinc diphenoxide [3],... 

Nonstereospecific aerobic epoxidations of alkenes in the presence of aldehydes catalyzed by nickel(II),298 iron(in),299 and cobalt(II)300 complexes, and clay-supported nickel acetylacetonate301,302 have been reported. A radical mechanism has been postulated. The involvement of active copper species and peracids were suggested in a similar reaction catalyzed by copper salts.303... 

Sachtler proposes a "dual site" mechanism where the hydrogen is dissociated on the Ni surface and then migrates to the substrate which is coordinated to the adsorbed nickel-tartrate complex. In this context it is of interest that the well known Sharpless epoxidation probably takes place on a dimeric tartrate complex of Ti. Sachtler suggests that both the anion and the cation have a function which varies according to the conditions used. It is not clear whether the spillover mechanism is also proposed for the reaction in solution [55]. 

Two reports have appeared on the catalyzed reaction of C02 with epoxides to form alkylene carbonates. One of the processes uses phosphine complexes of zerovalent nickel as the catalyst (157), and appears closely related to the more recent isolation of (PCy3)2Ni(C02) (115). Ethylene oxide reacts in benzene under 500 psi pressure of C02 in a stainless steel autoclave at 100°C to form ethylene carbonate with 95% selectivity, (77), using as the catalysts NiL2, L = PCy3 or PPh3. 

The. V-alkylation of ephedrine is a convenient method for obtaining tertiary amines which are useful as catalysts, e.g., for enantioselective addition of zinc alkyls to carbonyl compounds (Section D. 1.3.1.4.), and as molybdenum complexes for enantioselective epoxidation of allylic alcohols (Section D.4.5.2.2.). As the lithium salts, they are used as chiral bases, and in the free form for the enantioselective protonation of enolates (Section D.2.I.). As auxiliaries, such tertiary amines were used for electrophilic amination (Section D.7.I.), and carbanionic reactions, e.g., Michael additions (Sections D. 1.5.2.1. and D.1.5.2.4.). For the introduction of simple jV-substituents (CH3, F.t, I-Pr, Pretc.), reductive amination of the corresponding carbonyl compounds with Raney nickel is the method of choice13. For /V-substituents containing further functional groups, e.g., 6 and 7, direct alkylations of ephedrine and pseudoephedrine have both been applied14,15. 

Ni(II) complexes of cyclam and oxocyclam derivatives catalyze the epoxidation of cyclohexene and various aryl-substituted alkenes with PhIO and NaOCl as oxidants, respectively. In the epoxidation catalyzed by the Ni(II) cyclam complex using PhIO as a terminal oxidant, the high-valent nickel-oxo complexes (e.g., LNi -0, LNi=0, LNi -0-I-Ph, or LNi -0-Ni L) have been proposed as the active oxidant (92). In the reaction, E olefins are more reactive than the corresponding Z isomers, and a strong correlation was observed between the electron-donating effect of the para substituents in styrene and the initial reaction rate (91). Isotope labeling studies have shown that the epoxide oxygen is derived from PhIO. 

After screening several reductants in the aerobic epoxidation of olefins catalyzed by nickel(II) complexes, it was found that an aldehyde acts as an excellent reductant when treated under an atmospheric pressure of molecular oxygen at room temperature (Scheme 6). Similar reactions have been reported in the patents. Propylene was monooxygenated into propylene oxide with molecular oxygen in the coexistence of metal complexes and aldehyde such as acetaldehyde " or crotonaldehyde, but the conversion of olefin and the selectivity of epoxide were never reached satisfactory levels. Recently, praseodymium(III) acetate was also shown to be an effective catalyst for the aerobic epoxidation of olefins in the presence of aldehyde. ... 

The efficiency of nickel(II) complexes in the present epoxidation was demonstrated by taking epoxidation of 2-methyl-2-decene as a model reaction. Through the three experiments carried out in the presence of 4.0 mol%, 0.256 mol%, and 0.0096 mol% of Ni(dmp)2 against olefin, respectively (Table 9), it was found that, even in the case of employing only 0.0096 mol% of Ni(dmp)2, the epoxidation proceeded smoothly and the corresponding epoxide was obtained in 1020000% yield based on Ni(dmp)2. 

By combined use of molecular oxygen and aldehyde, various olefins are smoothly oxygenated into the corresponding epoxides catalyzed by bis(l,3-diketonato)nickel(II) complexes under an atmospheric pressure of oxygen at room temperature.[la, b] Transition-metal complex catalyst is quite influential over the reaction system of the present oxygenation, therefore, in order to develop the useful procedures, suitable selection of the catalyst is crucial. 

There has been a wide-ranging review of transmetalation reactions of arenes concentrating on the use of boron-containing compounds. The reaction of arylboronate esters and related compounds with alkyl halides is catalysed by copper(I) formation of an aryl—copper intermediate followed by an 5N2-type reaction with the alkyl electrophile is likely. Palladium complexed with a diimine is an excellent catalyst in the phenylation reaction of Michael acceptors with phenylboronic acid so as to yield products such as (16). The nickel-catalysed reaction of phenylboronic acid with styryl epoxides has been shown to yield a-substituted alcohols such as (17). 

Electrochemical synthesis of cyclic carbonates from CO2 with epoxides, anilines, alcohols, and glycols was reported [53-60]. For example, Dunach et al. [54] conducted the reaction of epoxides with CO2 to the corresponding cyclic carbonates by an electrochemical method in the presence of nickel(II) complexes. In these methods, harmful organic solvents, supporting... 

Hydrogenation catalyzed by palladium, platinum, or Raney nickel of 6 retains the stereogenic center of vicinal carbon, thus provides a complimentary access to chiral vicinal amino alcohols to the conventional routes such as asymmetric epoxide ring opening with amines and their related precursors. Employing lanthanum-(/ )-binaphthol complex to promote asymmetric nitroaldo reaction, followed by the reduction of nitro group, to form amino alcohols serves as the perfect example of this synthetic strategy. ... 

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