Nickel zerovalent transition

There are few reports of oxidative addition to zerovalent transition metals under mild conditions three reports involving group 10 elements have appeared. Fischer and Burger reported the preparation of aTT -allylpalladium complex by the reaction of palladium sponge with allyl bromide(63). The Grignard-type addition of allyl halides to aldehydes has been carried out by reacting allylic halides with cobalt or nickel metal prepared by reduction of cobalt or nickel halides with manganese/iron alloy-thiourea(64). 

Benn R, Bussemeier B, Flolle S, Jolly PW, Mynott R, Tkatchenko I, Wilke G (1985) Transition-metal allyls. 6. The stoichiometric reaction of 1,3-dienes with ligand modified zerovalent-nickel systems. J Organomet Chem 279 63-86... 

Transition metals with 3d electrons, such as iron, cobalt, nickel, and copper, are of great importance for catalysis, magnetism, and optics. Although the reduction of 3d-metal ions to zerovalent metals is quite difficult because of their lower redox potentials than those of noble metal ions, a production of 3d-transition metal/noble metal bimetallic nanoparticles is not so difficult. In 1993 we successfully set up a new method for the preparation of PVP-protected Cu/Pd bimetallic nanoparticles according to Eq. (2) [112-114]. 

Many transition metals catalyze oligomerization reactions between dienes and olefins or alkynes. Possible reaction products are legion. But it is almost exclusively with zerovalent nickel that cyclic products are formed. Addition of olefins or alkynes to catalysts mentioned in the previous section suppresses the cyclooligomerization and instead gives cyclo-co-oligomerization products. 

One strategy to ehminate side-reactions in NCA polymerizations is the use of transition metal complexes as active species to control addition of NCA monomers to polymer chain-ends. The use of transition metals to control reactivity has been proven in organic and polymer synthesis as a means to increase both reaction selectivity and efficiency [21]. Using this approach, substantial advances in controlled NCA polymerization have been realized in recent years. Highly effective zerovalent nickel and cobalt initiators (i.e. bpyNi(COD) [22,23] and (PMc3)4Co [24]) were developed by Deming that... 

This leads us to propose a theoretically verified, refined catalytic cycle for production of linear and cycHc CiQ-olefin products (cf. Scheme 3). Furthermore, a detailed comparison of crucial mechanistic aspects of the catalytic reaction course for co-oligomerization of butadiene and ethylene and for cyclooligomerization of butadiene promoted by zerovalent bare nickel complexes was undertaken. These contribute (first) to a more detailed understan(fing of mechanistic aspects of the [Ni"]-mediated co-oHgomerization of 1,3-dienes and olefins and (second) to a deeper insight into the catalytic structure reactivity relationships in the transition-metal-assisted co-oHgomerization and oligomerization reactions of 1,3-dienes. 

The next question to be asked concerns the composition of the particles. For the case of monometallic particles this could in principal be a trivial question. If the particle is known to contain a single element, the only question which then arises concerns the oxidation states of the metal, and this can be determined by X-ray photoelectron spectroscopy. For example, the colloidal metals described in Section 6.2.2.1 and prepared by Dye and coworkers by alkalide and electride reduction of salts of gold, copper, platinum, nickel, and molybdenum (as well as several main group metals and metalloids) were analyzed by XPS [73] which showed the presence of only zerovalent metal. Oxidized metal was detected only for nickel and molybdenum (among the transition metals) and this only after exposure to an oxidizing solvent such as methanol. These results show that if a sufficiently powerful reducing agent is used in the colloid synthesis, the surface of the particles can be kept in a reduced metallic state. 

In conclusion, oxidative addition of aryl halides to metallic nickel proceeded smoothly under mild conditions, and the corresponding biaryls were obtained in good yields. The present reaction is superior to the Ullmann synthesis in the scope of the reaction conditions [125] and to the coupling reaction of Grignard reagents catalyzed by transition metals [133]. Finally, because of the simple and easy procedure for the preparation of nickel powder, it is far more convenient to work with than zerovalent nickel complexes such as tetrakis(triphenylphosphine)nickel(0) or bis(l,5-cyclooc-tadiene)nickel(O) [128]. 

In cathodic coupling (Figure 4.4) reduction of the dihalogenated monomer occurs catalytically by its previous oxidative addition to a low-valent transition metal complex (usually the zerovalent nickel bipyridyl... 

Allyl Complexes and Complexes Derived from Mono-ol ns Zerovalent Nickle, Platinum, and Palladium.— A series of complexes Ni(ol) (x=l—3, ol=alkyl, chloro, or fluoro olefin) has been detected by matrix condensation of nickel atoms with the olefin the optical spectra show a correlation between the transition energies of the Ni(ol) species and the 7r -orbital energy of... 

---