Q2. What is the disadvantage of allyl complexes with electron-drawing substituents?
To circumvent the disadvantage of slow activation, substituted allyl complexes with electron-withdrawing substituents [67] have been used recently in combination with Lewis acids.
Q3. How can a cationic complex be prepared?
In the presence of a suitable neutral bidentate ligand and a halide abstracting agent, cationic complexes can be obtained directly [55,56].
Q4. What type of complexes have been used for the polymerization of olef?
Another class of cationic chelate-stabilized alkyl compounds, which have been applied as catalyst precursors and for mechanistic studies, are complexes of the type 5.
Q5. What is the general route to complexes of ligands sensitive to MeLi?
Canty and coworkers have also proposed displacement of pyradizine from [(pyridazine)PdMe2]n as a general route to dimethyl complexes of ligands sensitive to MeLi [24,42,43a].
Q6. What is the common method of preparation of dimethyl complexes?
The dimethyl complexes [(L L)MMe2] are usually prepared by alkylation of a suitable Pd(II), respectively Ni(II) precursor with a main group methyl compound, such as MeLi or a Grignard reagent.
Q7. How can the palladium dimethyl complexes be handled?
In general, the palladium dimethyl complexes can be handled at r.t. under a protective gas atmosphere, although storage should occur at low temperature.
Q8. How can a di(trimethylsilyl) complex be prepared?
Di(trimethylsilyl) complexes [(L L)Ni(CH2SiMe3)2] can be prepared from [(py)2Ni(CH2SiMe3)2], the py ligands of which are easily displaced by a variety of ligands (also by tmeda) [51].
Q9. How can the authors obtain palladium dialkyl complexes?
Palladium dialkyl complexes [(L L)PdR2] (L L=dppe, bipy) can also be obtained by reaction of [Pd(acac)2] with R2Al(OEt) (e.g. R=Me, Et) in the presence of L L [44].
Q10. What is the role of allyl complexes in the catalytic cycle?
Much of the pioneering work in this field has relied on these complexes, and allyl complexes may be regarded as the first well-defined organometallic late transition metal complexes used as catalyst precursors for these reactions [61].
Q11. What is the current demand for catalyst discovery?
The current surge of interest in catalyst discovery via automated parallel syntheses [15] further underlines this demand, e.g. for screening of new ligands.
Q12. What is the effect of the in situ preparation of h3-allyl complexes?
for the general case of utilization of the above in situ preparation methods with new multidentate ligands, it may be speculated that formation of inactive h3-allyl complexes may diminish catalyst activity (cf. Section 3), and that the conditions of catalyst preformation (time, temperature) may have a strong influence.
Q13. What mechanism is there for insertion of monomers into Pd C bonds?
Concerning the mechanism of chain propagation, there is strong evidence for an insertion-type mechanism, i.e. insertion of monomers into Pd C bonds.
Q14. What is the role of aryl substituents in the development of catalysts?
In nickel(II) complexes containing an anionic bidentate ligand (cf. Section 1), h1-s-bound aryl substituents have played an important role in the development of well defined catalyst precursors.
Q15. What is the common type of ligand used in the Shell process?
The latter class of ligands is exemplified by the anionic chelating P,O-ligands already referred to, nickel(II) complexes of such ligands being the basis of the Shell Higher Olefin Process, i.e. the linear oligomerization of ethylene to a-olefins.
Q16. What is the effect of adding Lewis acids to aluminum alkyl cocatalyst?
Addition of Lewis acids such as B(C6F5)3 has been claimed to reduce the amount of aluminum alkyl cocatalyst required in such systems [110].