Wilke’s complex

Interestingly, the specific environment of the ionic solvent system appears to activate the chiral Ni-catalyst beyond a simple anion-exchange reaction. This becomes obvious from the fact that even the addition of a 100-fold excess of Fi[(CF3S02)2N] or Na[BF4] in pure, compressed CO2 produced an at best moderate activation of Wilke s complex in comparison to the reaction in ionic liquids with the corresponding counter-ion (e.g., 24.4 % styrene conversion with 100-fold excess of Fi[(CF3S02)2N], in comparison to 69.9 % conversion in [EMIM][(CF3S02)2N] under otherwise identical conditions). 

Hydrovinylation is the transition metal catalyzed co-dimerization of alkenes with ethene yielding 3-substituted 1-butenes [26]. This powerfid carbon-carbon bond forming reaction can be achieved with high enantioselectivity using Wilke s complex as a catalyst precursor [27]. In conventional solvents, this pre-catalyst needs to be activated with a chloride abstracting agent, e.g. Et3Al2Cl3. Leitner et al. reported the... 

The second pathway is represented by Eqs. (8)—(11). These reactions involve reduction of the Nin halide to a Ni° complex in a manner similar to the generation of Wilke s bare nickel (37, 38) which can form a C8 bis-77-alkyl nickel (17) in the presence of butadiene [Eq. (9)]. It is reasonable to assume that in the presence of excess alkyaluminum chloride, an exchange reaction [Eq. (10)] can take place between the Cl" on the aluminum and one of the chelating 7r-allyls to form a mono-77-allylic species 18. Complex 18 is functionally the same as 16 under the catalytic reaction condition and should be able to undergo additional reaction with a coordinated ethylene to begin a catalytic cycle similar to Scheme 4 of the Rh system. The result is the formation of a 1,4-diene derivative similar to 13 and the generation of a nickel hydride which then interacts with a butadiene to form the ever-important 7r-crotyl complex [Eq. (11)]. 

Moving across the /-block results in an increase in number of M-Si-bonded derivatives, and group 6 is the first group for which significant numbers of compounds are known for all members of the triad. The complexes covered in Corey and Braddock-Wilking s review3 will not be discussed again in this section. 

Garlin, R. T. and Wilkes, J. S., Complexation of CP2MCI2 in a chloroaluminate molten-salt. Relevance to homogeneous Ziegler-Natta catalysis, /. Mol. Catal., 63,125,1990. 

Wilke s reaction was the same except that Al-H was added across a 7r-complexed olefin. This supports the Natta mechanism for Ziegler... 

Both of these facts do explain the nickel effect. The first finding is the basis for the syntheses of Wilke s nickel(0)-olefin complexes (1 and 2) [Eq. (3)] 10), while the second reflects the fact that 1, 2, and (C2H4)3Ni(0) (3), which is obtained from 1 and ethylene 11, 12), are highly active catalysts for the transalkylation of aluminum alkyls with olefins as, for example in Eq. (4) 11, 13). 

Orlowski, M. and Wilk, S. (2000) Catalytic activities of the 20 S proteasome, a multi-catalytic proteinase complex. Arch.Biochem.Biophys., 383, 1-16. 

In spite of the modest asymmetric induction it was concluded that at least one of the chiral ligands is coordinated to the nickel in the catalyticaUy active species. An alternative interpretation was given by Wilke and coworkers [29]. They could show that (methylsalicyhdene)dimethylaluminum forms a stable adduct with nickel(O) complexes. It was concluded that the asymmetric induction in Pino s experiment might be attributed to a complex in which the chiral Hgand is complexed to the Lewis acidic aluminum. 

---