Insertion reactions of alkenes

The ring-opening mechanism was well supported by the snapshots and the overlap bond population obtained from TB-QCMD simulations, where the formation of new C-H and La-C bonds and the dissociation of La-H and proximal C-C bonds could be tracked. The obtained dynamic ring opening mechanism was similar to the static mechanism, however, a novel transition state was also proposed for insertion reaction of alkenes, with tetrahedral h4-coordination. This example perfectly illustrates the importance of mutual interplay between high-level first principle methodologies and simplified methodologies derived from ab initio quantum chemistry, massively applicable for real systems. 

Reactions of this type are postulated as equilibria in synthetically important insertion reactions of alkenes, alkynes and other unsaturated molecules into the Pd-C bonds of dimeric palladacycles.271,272 Further, this reaction can form the basis for... 

Intramolecular insertion reactions of alkenes into cyclobutanone C-C bonds were catalyzed by cationic rhodium(l) complexes (Scheme 3.45) [54]. 3-(2-Vinylphenyl)cyclobutanone 81 were transformed into ketone 82 having a bicyclo[3.2.1] skeleton. 

Table 3 Stoichiometric C-H Insertion Reactions of [Fe(F20-TPP)C(Ph)CO2Et] 2 and [(MeIm)Fe (F2o-TPP)CPli2] 4 with Alkenes or Tetrahydrofuran...

RMn(CO)5.3 Alkylmanganese pentacarbonyl complexes are obtained by reaction of alkyl halides with NaMn(CO),. Under pressures of 2-10 kbar, these complexes undergo an insertion reaction with alkenes to give usually a single manganacycle in which the electron-withdrawing group of the alkene is attached to the same carbon atom as the metal. Demetallation is accomplished by photolysis... 

In this chapter we will discuss some aspects of the carbonylation catalysis with the use of palladium catalysts. We will focus on the formation of polyketones consisting of alternating molecules of alkenes and carbon monoxide on the one hand, and esters that may form under the same conditions with the use of similar catalysts from alkenes, CO, and alcohols, on the other hand. As the potential production of polyketone and methyl propanoate obtained from ethene/CO have received a lot of industrial attention we will concentrate on these two products (for a recent monograph on this chemistry see reference [1]). The elementary reactions involved are the same formation of an initiating species, insertion reactions of CO and ethene, and a termination reaction. Multiple alternating (1 1) insertions will lead to polymers or oligomers whereas a stoichiometry of 1 1 1 for CO, ethene, and alcohol leads to an ester. 

Reactions of alkenes and alkynes that generate a carbon-metal bond by nucleophilic addition to a metal ir-complex and subsequently undergo carbon monoxide insertion to yield a carbonyl product are... 

Higher n/b ratios in cobalt-modified catalysts are apparently achieved as a result of the phosphine presenting more steric bulk to the insertion reaction of the alkene. The effect is predominately steric, since there is little correlation with regiochemistry and phosphine bacisity. A combination of electronic (Xi) and steric (cone angle 0) effects provide a more rational explanation of the increase in nib ratio with added phosphines.16,17... 

Aviv and Gross developed an interesting insertion reaction of diazo compounds into a secondary amine-hydrogen bond in the presence of Fe-corrole complexes (Scheme 7.8) [12], Competition experiments performed in the presence of an amine and an alkene revealed the N—H-insertion reaction to be much faster than the cyclopropanation of the C=C bond. Apart from this chemoselectivity issue, the reactions are characterized by their very short reaction times most insertion reactions were completed within 1 min at room temperature. Most recently, Woo s group reported on a similar process using commercially available iron tetraphenyl-porphyrin [Fe(TPP)] dichloride [13]. 

The insertion reactions of CO, alkenes, and alkynes are particularly important. An early example (Berthelot, 1869) is ... 

There are relatively few well-defined insertion products of alkenes into M—alkyl bonds, although in catalytic systems this reaction can be very fast. An example is the single insertion of propene into a Zr—benzyl bond 182... 

Dirhodium(ll) tetrakis[methyl 2-pyrrolidone-5(R)-oarboxylate], Rh2(5R-MEPV)4, and its enantiomer, Rh2(5S-MEPY)4, which is prepared by the same procedure, are highly enantioselective catalysts for intramolecular cyclopropanation of allylic diazoacetates (65->94% ee) and homoallylic diazoacetates (71-90% ee),7 8 intermolecular carbon-hydrogen insertion reactions of 2-alkoxyethyl diazoacetates (57-91% ee)9 and N-alkyl-N-(tert-butyl)diazoacetamides (58-73% ee),10 Intermolecular cyclopropenation ot alkynes with ethyl diazoacetate (54-69% ee) or menthyl diazoacetates (77-98% diastereomeric excess, de),11 and intermolecular cyclopropanation of alkenes with menthyl diazoacetate (60-91% de for the cis isomer, 47-65% de for the trans isomer).12 Their use in <1.0 mol % in dichloromethane solvent effects complete reaction of the diazo ester and provides the carbenoid product in 43-88% yield. The same general method used for the preparation of Rh2(5R-MEPY)4 was employed for the synthesis of their isopropyl7 and neopentyl9 ester analogs. 

A similar strategy faces difficulty in the case of addition products. The only products that could not be formed by dimerization of the corresponding silirane intermediates are the four-membered ring compounds (disilacyclobutanes in the reactions of alkenes and disilacyclo-butenes in the case of alkynes). But these four-membered ring compounds may well be formed by further insertion of difluorosilylene into intermediate three-membered silacycles, for example ... 

Sulfur dioxide reacts generally with transition metal alkyl, aryl, and a-allyl complexes to give sulfinate complexes. The reaction, first described in 1964 by Wojcicki and Bibler, resembles well-known insertion reactions of CO, C2F4, SnCl2, tetracyanoethy-lene, and other unsaturated species into metal-alkyl bonds, but there are important stereochemical and mechanistic differences Sulfur dioxide insertion into metal-alkene and metal-alkyne bonds have not been reported. However, PdCl2 has been used as a catalyst for copolymerization of ethylene and SO2 to polysulfones and insertion into a Pd-ethylene bond is a conceivable reaction step. 

The four ttutin characteristic reactions of nitrenes are summarized in Scheme 2. All of these reactions have parallels in carbene chemistry for example, a full discussion of the C—insertion reaction of car-benes is given in Volume 3, Ch ter 4.2. The first reaction, the addition to an alkene to form an aziridine, is covered in detail in Volume 7, Chapter 3.S. The C—insertion reaction, the subject of this chapter, can, in principle, occur by severid mechanisms. However nx>st of the reactions are believed to involve... 

The reaction of alkenes with carbene gives cyclopropane as a major product by cycloaddition reactions but products in which methylene is inserted into the C-H single bond are also obtained. 

Insertion reactions involving metal alkoxides are also known. For example, carbon dioxide is known to react with some metal alkoxides as shown in equation (12). The formation of a bidentate ligand is a significant thermodynamic driving force for some of these reactions. The isoelectronic aryl and alkyl isocyanates and carbodiimides can react similarly. Insertion reactions involving alkenes and carbon monoxide are known for platinum alkoxides. 

Insertion reactions [81], alkene additions [82] and even additions to benzene and hexafluorobenzene [83] have been observed using these sources of carbenes, as shown in Figure 6.53. 

Transmetallation of organomercurials by Pd and subsequent ligand insertion is also useful in organic synthesis e.g., the reaction of alkenes, organomercurials and Pd salts is used to replace a vinyl hydrogen by an alkyl or aryl moiety ... 

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