Nickel Transition Metal Catalysis

The first example of homogeneous transition metal catalysis in an ionic liquid was the platinum-catalyzed hydroformylation of ethene in tetraethylammonium trichlorostannate (mp. 78 °C), described by Parshall in 1972 (Scheme 5.2-1, a)) [1]. In 1987, Knifton reported the ruthenium- and cobalt-catalyzed hydroformylation of internal and terminal alkenes in molten [Bu4P]Br, a salt that falls under the now accepted definition for an ionic liquid (see Scheme 5.2-1, b)) [2]. The first applications of room-temperature ionic liquids in homogeneous transition metal catalysis were described in 1990 by Chauvin et al. and by Wilkes et ak. Wilkes et al. used weekly acidic chloroaluminate melts and studied ethylene polymerization in them with Ziegler-Natta catalysts (Scheme 5.2-1, c)) [3]. Chauvin s group dissolved nickel catalysts in weakly acidic chloroaluminate melts and investigated the resulting ionic catalyst solutions for the dimerization of propene (Scheme 5.2-1, d)) [4]. 

It is about 20 years since the combination of transition-metal catalysis and electroreduction was shown to be applicable to the coupling of organic molecules. This was followed by a number of fundamental investigations and basic syntheses using various nickel, cobalt, or pdladium compounds which can easily be reduced in situ electrochemically to low-valent reactive intermediates. The last decade has been less characterized by reports on new catalytic systems than by the development of new synthetic applications. The aim of this review is to show that the electrochemical processes described here offer valuable advantages in organic synthesis. 

Bicyclopropylidene (1) also reacts with activated alkenes under transition-metal catalysis. With electron-deficient alkenes under nickel(O) catalysis, the [2-1-2] cycloadduct 263 was the main component in the reaction mixture [2b, 150]. Under palladium(O) catalysis, formal [3-1-2] cycloaddition of electron-deficient (Scheme 60) as well as strained alkenes can be achieved exclusively... 

It is worth mentioning that the synthesis of allenes from propargyl halides in Grignard reactions is favored by transition metal catalysis more than by the participation of allenic carbene intermediates in as much as the level of metal impurities in magnesium turnings is not reduced to a minimum, or metal salts such as ferric chloride and other metal chelates such as nickel acetoacetonate are added to the reaction mixture. ... 

Our synthetic method for CO2 fixation was based on the use of transition-metal catalysis combined with electrochemical techniques [10]. Within this methodology, the electrochemical CO2 fixation into some alkenes has been reported to afford carbo lic acids in a reductive hydrocarboxylation-tjqje reaction catalyzed by nickel complexes, under mild conditions [11]. The electrocarboxylation of organic halides to the corresponding carboxylic acids has also been reported [12], yields and efficiency of the reaction being strongly dependent on the reaction conditions. 

As early as 1948, Reppe et al. reported the discovery of the cyclic polymerization of acetylene to cyclooctatetraene (eq. (29)) using nickel catalysts [84]. This discovery represented a true landmark in transition metal catalysis. 

Negishi, E., King, A. O., Okukado, N. Selective carbon-carbon bond formation via transition metal catalysis. 3. A highly selective synthesis of unsymmetrical biaryls and diarylmethanes by the nickel- or palladium-catalyzed reaction of aryl- and benzylzinc derivatives with aryl halides. J. Org. Chem. 1977,42, 1821-1823. 

Negishi, E. Selective carbon-carbon bond formation via transition metal catalysis is nickel or palladium better than copper in Aspects Mech. Organomet. Chem., [Proc. Symp.] (ed. Brewster, J. H.), 285-317 (Plenum, New York, 1978). 

Asymmetric modifications of hydrovinylation are one of the earliest examples of successful asymmetric transition metal catalysis. After optimization of various dimerization and codimerization reactions using phosphane modified nickel catalysts, the first examples of asymmetric olefin codimerization were reported with n-allylnickel halides activated by organoaluminum chloride and modified by chiral phosphanes7. Thus, codimerization of 2-butene with propene using n-allylnickel chloride/A]X, (X = Cl, Br) in the presence of tris(myrtanyl)phosphane gives low yields of (—)-( )-4-methy 1-2-hexene (I) with 3% ee7,7 . 

Low-valent transition metal catalyzed versions of [2 + 2] cycloadditions. especially with nickel catalysts, were recognized early as useful alternatives to thermal and photochemical methods12-15. The observation of transition metal catalysis, active in [2 + 2]-cycloaddition reactions, originally caused considerable discussion of the mechanism as an inversion of symmetry rules, effected by the transition metal, may be assumed. Thus, it was suggested that, in the presence of the metal catalyst, a forbidden reaction becomes allowed 16,17. This interpretation, however, could not be verified for the overall process, since experimental investigations revealed a stepwise mechanism with metallacycle intermediates18-23. 

Until recently, access to optically active 3-hydroxyalkanoates by enantioselective transition metal catalysis was based primarily on the heterogeneous hydrogenation of 3-oxo esters by Raney nickel modified with tartaric acid and sodium bromide (see Section 2.3.1.1.). As far as homogeneous catalysis is concerned, the best optical induction (71 % ee) in the hydrogena-... 

Carbon monoxide is unusual in that it has a lone pair of electrons on carbon C=0-. It is also isoelectronic with N2, so you might imagine that CO would be equally unreactive. Moreover, both substances have high bond energies (1072 kj/mol for C=0 and 941 kj/mol for N N). Because of the lower nuclear charge on carbon (compared with either N or O), however, the lone pair on carbon is not held as strongly as that on N or O. Consequently, CO is better able to function as an electron-pair donor (Lewis base) than N2. It forms a wide variety of covalent compoimds, known as metal carbonyls, with transition metals. Ni(CO)4, for example, is a volatile, toxic compound that is formed by simply warming metallic nickel in the presence of CO. The formation of metal carbonyls is the first step in the transition-metal catalysis of a variety of reactions of CO. 

Plenum Press, New York, 1978, 285-317. Selective Carbon-Carbon Bond Eormation Via Transition Metal Catalysis Is Nickel or Palladium Better than Copper ... 

A useful method would not require special conditions, be quite general and use easily prepared starting materials. This can be done with transition-metal catalysis (Scheme 2.1). By far the most widely used metal is palladium, but other metals, especially nickel and, more recently, iron, have also been employed. ... 

The availability of newer, more effective methods for aryl aryl coupling has been an important driving force for the development of new synthetic strategies for PPPs and other polyarylenes. Transition metal catalysis, such as the Pd(0)-catalyzed aryl-aryl coupling developed by Suzuki [63] and nickel(0)-catalyzed or -mediated coupling... 

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