Alkenes 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]. 

During the coverage period of this chapter, reviews have appeared on the following topics reactions of electrophiles with polyfluorinated alkenes, the mechanisms of intramolecular hydroacylation and hydrosilylation, Prins reaction (reviewed and redefined), synthesis of esters of /3-amino acids by Michael addition of amines and metal amides to esters of a,/3-unsaturated carboxylic acids," the 1,4-addition of benzotriazole-stabilized carbanions to Michael acceptors, control of asymmetry in Michael additions via the use of nucleophiles bearing chiral centres, a-unsaturated systems with the chirality at the y-position, and the presence of chiral ligands or other chiral mediators, syntheses of carbo- and hetero-cyclic compounds via Michael addition of enolates and activated phenols, respectively, to o ,jS-unsaturated nitriles, and transition metal catalysis of the Michael addition of 1,3-dicarbonyl compounds. ... 

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... 

Halocarbons are known to add to alkenes under transition metal catalysis. The reaction proceeds via radicals and was first described by Kharasch and coworkers in 1945 (Scheme 3.9) [73-76],... 

The reaction is catalysed by many transition-metal complexes, and a mechanism for the hydrosilylation of an alkene under transition-metal catalysis is depicted in Figure Si5.7. Initial coordination of the alkene to the metal is followed by cis addition of the silicon-hydrogen bond. A hydride migratory insertion and elimination of the product silane complete the cycle. 

The hydrophosphonylation (addition of dialkyl phosphonates), hydrophos-phinylation (addition of alkyl alkylphosphinates or alkyl phosphinates) and addition of secondary phosphine oxides to unfunctionalized alkenes and alkynes occur under free radical conditions or with transition metal catalysis.10,39 63 90... 

Other fused thiiranes are more thermally stable. For example, the compound 45 desulfurizes at 160 °C (Scheme 11) <1987JA3801, 1990JA3029>. The reaction provided alkenes with retention of stereochemistry. In the presence of a desulfurizing agent such as phosphines or phosphites, the desulfurization temperature may be decreased to room temperature (Section 1.06.6.6) <1984CHEC(7)131>. The desulfurization of thiiranes is also subjected to transition metal catalysis. Since the initial step involves coordination of the metal to thiirane sulfur atom, the topic is discussed further in Section 1.06.6.4. 

Bifiinctional conjunctive reagents (BCRs), such as a 1,3-substituted 2-methylenepropane (96), can serve as effective TMM synthons via transition metal catalysis. In this case, the transition metal complex can promote the elimination of the elements X—Y from (96) to form a coordinated TMM species. Cycli-zation of this intermediate with an alkene thus produces the methylenecyclopropane product and also regenerates the catalyst (Scheme 5). In the last decade a number of BCRs utilizing this concept, or some modifications thereof, has been developed for various TMM synthons. ... 

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... 

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. 

Christoffers, J. Transition-metal catalysis of the Michael reaction of 1,3-dicarbonyl compounds and acceptor-activated alkenes. Eur. J. Org. Chem. 1998, 1259-1266. 

The silicon hydrides do not spontaneously add to alkenes either. However, the hydrosilation, or hydrosilylation reaction, of olefins is of significant utility in the preparation of alkyl-subtituted silanes with the use of either radical or transition metal catalysis. The preferred metal catalysts for hydrosilation are platinum complexes. Chloro-platinic acid will catalyze hydrosilations with halosilanes, alkylarylhalosilanes, alkoxy-silanes, and siloxanes that in many cases are quantitative under ambient conditions. Yields and conversions are generally poorer for alkyl,- and arylsilanes. Many other coordination complexes have been found to catalyze the hydrosilation reaction, and these can provide certain advantages, particularly in regiochemistry. Some typical hydrosilation reactions are shown in Table... 

Transition metal catalysis of the Michael reaction of 1,3-dicarbonyl compounds with acceptor activated alkenes has been known since the early 1980 s 2>3 It is a valuable alternative to the classic base catalysis of the reaction. Because of the mild and neutral conditions, the chemoselectivity of these reactions is superior to that provided by base catalysis, since the latter suffers from various unwanted side or subsequent reactions, such as aldol cyclizations, ester solvolyses or retro-Claisen type decompositions. A number of transition metal and lanthanide compounds have been reported to catalyze the Michael reaction, but FeCb 6 H20 is one of the most efficient systems to date. A number of 3-diketones or p-oxo esters and MVK are cleanly converted to the corresponding Michael reaction products within a few hours at room... 

R. Noyori shared the Nobel Prize in Chemistry in 2001 with W. S. Knowles, who pioneered the use of Rh-catalyzed asymmetric hydrogenation, and K. B. Sharpless, who is known for fundamental work on asymmetric epoxidation and dihydroxylation of alkenes involving transition metal catalysis. 

Previously in Chapter 12 we have seen several examples of cydization reactions that have involved transition metal catalysis. In Chapter 11, we introduced Mo- and Ru-catalyzed RCM as a means of converting acyclic dienes, alkene-alkynes, and dialkynes into rings containing carbon-carbon double and triple bonds. Section 12-5 will cover a few cases where organotransition metal complexes effectively promote the construction of rings where two or more C-C bond connections occur during the same transformation. Some examples will be extensions of reactions already covered, whereas others will entail new chemistry. 

Perhaps the most common method for the epoxidation of simple alkenes is their reaction with peroxyacids, which has occasionally been referred to as the Prilezhaev (Prileschajew) reaction. O This reaction does not require transition metal catalysis and the yield of epoxide is often high. Peroxyacids such as 156 are prepared by reaction of carboxylic acids with hydrogen peroxide. An equilibrium is established during the reaction that favors the peroxyacid, although several alternative methods are available.279 in general, strong... 

---