Other transition metal-catalyzed reactions

Iridium complexes as well as [Rh(OH)(cod)]2 can catalyze the Mizoroki-Heck-type reaction of arylsilanediols with acrylates. Aryltrialkoxysilanes activated by TBAF also work as the aryl donor in the presence of H20. In contrast to the Rh-catalyzed reaction, this reaction does not form / -arylated saturated esters even in aqueous media.69 

Fu and Powell have reported that a nickel-based catalyst accomplishes an efficient cross-coupling between secondary alkyl bromides and aryltrifluorosilanes activated by CsF (Equation (14)).70 This arylation is tolerant to a variety of functionalities and applicable to primary alkyl bromides and iodides. 

Under catalysis by an Ru complex, alkynylsilanes react with pyridines to give ( )-2-alkenylated pyridines (Equation (15)).71 This regio- and stereoselective direct alkenylation has been proposed to proceed via cationic Ru vinylidene complex 9. 

Besides the well-documented Cu- and V-catalyzed asymmetric oxidative biaryl coupling reactions, the reactions catalyzed by chiral complexes based on other transition metals such as Ru and Fe have also appeared in the literature. 

Based on the previously described mechanistic details, the asymmetric cross-coupling reactions between two 2-naphthol molecules with different electronic properties can be expected, which will allow the facile production 

Guided by the preliminary DFT calculations, Kiirti and co-workers envisioned that although two possible regioisomeric [3,3]-rearrangement pathways might exist, the desired BINAM derivatives should be formed exclusively 

Based on their successes in developing catalytic asymmetric Fischer indole synthesis, List and co-workers further carried out [3,3]-rearrangement reactions of At,At -binaphthyl hydrazines to deliver BINAM products. In this case, (i )-35 was also proved to be the best catalyst. The addition of weakly acidic CG-50 resin as an additive could allow the reaction to be performed at a relatively low catalyst loading (5 mol%). A number of Af,Ar-binaphthyl hydrazine substrates with electronically diverse substituents could be converted to their corresponding products in good yields and enantioselectivity. 

Few studies are focused on the use of Col2(dppe)/Zn [176], NiClj-bH O/TBAB [177], [(NHC)-Ni(aUyl)Cl] [178], and Ni/NHC [179] for the coupling of aryl halides with aiyl and alkyl thiols. 

---

In addition to the applications reported in detail above, a number of other transition metal-catalyzed reactions in ionic liquids have been carried out with some success in recent years, illustrating the broad versatility of the methodology. Butadiene telomerization [34], olefin metathesis [110], carbonylation [111], allylic alkylation [112] and substitution [113], and Trost-Tsuji-coupling [114] are other examples of high value for synthetic chemists. 

Asymmetric synthesis of tricyclic nitro ergoline synthon (up to 70% ee) is accomplished by intramolecular cyclization of nitro compound Pd(0)-catalyzed complexes with classical C2 symmetry diphosphanes.94 Palladium complexes of 4,5-dihydrooxazoles are better chiral ligands to promote asymmetric allylic alkylation than classical catalysts. For example, allylic substitution with nitromethane gives enantioselectivity exceeding 99% ee (Eq. 5.62).95 Phosphi-noxazolines can induce very high enatioselectivity in other transition metal-catalyzed reactions.96 Diastereo- and enantioselective allylation of substituted nitroalkanes has also been reported.9513... 

The previous sections were dedicated to the transition metal catalytic reactions that have been widely studied using QM/MM methods. In this section, other transition metal catalyzed reactions that have also had QM/MM methods applied to them are briefly discussed. 

The reductive elimination to form C-C and C-H bonds [45] is a crucial step in the cross-coupling processes, as well as many other transition metal-catalyzed reactions. Reductive elimination reactions comprise an early chapter in any organometallic text. Many examples of these reactions have been studied, and a great deal is known about the mechanisms of these processes. Similarly, the cleavage of C-H bonds by oxidative addition, including the C-H bond in methane, is now known [46]. Again, questions remain about how these reactions occur, but a variety of mechanistic studies have revealed key features of these reactions. Even some remarkably mild C-C cleavage reactions have now been observed with soluble transition metal complexes [47,48]. 

A series of l-silyl-2-N(0 or B)-substituted ethenes (with high preference of isolated E isomers) were synthesized in the presence of ruthenium complexes (Eq. 28) [51-53] (B. Marciniec, M. Jankowska, M. Zaidlewicz, J. Cytarska, unpublished results). The reaction opens a general synthetic route for 1-silyl-2-heteroatom-substituted ethenes. The compounds of this kind, for example, /Talkoxysubstituted vinylsilanes are difficult to synthesize by other transition-metal-catalyzed reactions. 

Transition metals have already established a prominent role in synthetic silicon chemistry [1 - 5]. This is well illustrated by the Direct Process, which is a copper-mediated combination of elemental silicon and methyl chloride to produce methylchlorosilanes, and primarily dimethyldichlorosilane. This process is practiced on a large, worldwide scale, and is the basis for the silicones industry [6]. Other transition metal-catalyzed reactions that have proven to be synthetically usefiil include hydrosilation [7], silane alcdiolysis [8], and additions of Si-Si bonds to alkenes [9]. However, transition metal catalysis still holds considerable promise for enabling the production of new silicon-based compounds and materials. For example, transition metal-based catalysts may promote the direct conversion of elemental silicon to organosilanes via reactions with organic compounds such as ethers. In addition, they may play a strong role in the future... 

As with other transition metal-catalyzed reactions (Ziegler-Natta polymerization of alkenes, olefin metathesis), the mechanism of the Heck reaction is complicated. In brief, the species that reacts with the aryl halide is I Pd, where L is a ligand such as tiiphenylphosphine. By a process known as oxidative addition, palladium inserts into the carbon-halogen bond of the aryl halide. 

Rhodium-catalyzed reactions Copper-catalyzed reactions Ruthenium-catalyzed reactions Cobalt- and iron-catalyzed reactions Other transition metal-catalyzed reactions Cyclopropanation without transition metal catalysts Cyclopropanation of dihalocarbenes... 

---