Reaction with an olefin

The methylidene complex [E] is the true catalyst, which as far as we can tell has the shortest half-life, and its reaction with an olefin produces ethylene as a by-product. 

Reaction with an olefin to form a carbonium ion of higher molecular weight... 

Metal hydride species can undergo an insertion reaction with an olefinic double bond, resulting in the formation of a metal alkyl species which then generates the requisite carbenoids by a-hydride abstraction [110-112] ... 

In one case, at least, such a chelated complex has been shown to undergo the arylation reaction with an olefin. This example is the reac-... 

The cobalt—hydride intermediate has not been isolated and is virtually undetected. Cobalt hydride reaction with an olefin by first migrating the hydrogen atom from cobalt to a porphyrin nitrogen atom (78) or carbon atom (79) is precedented by the isomerization of a benzylcobalt chelate. In that case, the benzyl migrates reversibly from the cobalt to the carbon atom of the equatorial ligand.253... 

The reaction of 2 with FI202 in aqueous solution to form the corresponding Fe =0 complex has been reported [63]. The isosbestic behavior observed in the conversion as monitored by UV-vis spectroscopy favored the direct conversion of Fe to Fe =0 without the involvement of an Fe(III) intermediate. This observation opens the door for fhe inclusion of an Fe(II)/Fe(IV) cycle in the mechanistic landscape for olefin oxidation (see box in Fig. 18.4). Indeed, such a cycle was determined to be energetically feasible in a recent computational study of the reaction of H2O2 wifh a tetradentate ligand analog of 2. The initial Fe°(HOOH) adduct evolved to form Fe (OFI)2 after 0-0 bond cleavage and then Fe =0(0H2) subsequent to proton transfer. Upon reaction with an olefin, the former would afford the diol product, while the latter would afford the epoxide product [62]. 

Precursor of dichlorocarbene. Treatment of chloral with potassium /-butoxide at about 0° leads to dichlorocarbene, as shown by the reaction with an olefin.1... 

The benzocyclobutene functionality can thermally form an intermediate that can function as the diene partner in a classical Diels-Alder ring-forming reaction with an olefin. When benzocyclobutene and olefin are located on two immiscible polymers, the reaction can in theory lead to copolymer formation. Dean (1993) has postulated that copolymer is formed when 50-15 parts benzocyclobutene-terminated polyarylate is mixed with olefin-containing EPDM in an internal mixer at 265 °C. Blends were characterized by mechanical properties and DMTA. 

The Meyer report demonstrates that the activity of Ru catalyst 1 can be enhanced by the simple addition of phenol. In some instances, the addition of phenol has led to a 10-fold increase in catalyst lifetime and significantly higher turnover numbers. The phenol additive has also exhibited an effect on metathesis reactions catalyzed by Ru catalyst 3. Mechanistic studies (NMR, DFT calculations) suggest that phenol influences the kinetics of phosphine association and dissociation, and can activate the carbene carbon for reaction with an olefinic substrate. 

Active-methylene compounds are converted into the corresponding thioketones by successive reaction with thionyl chloride and triphenylphosphine. The thioketones thus prepared are too unstable to be isolated, and they undergo dimerization to give the 1,3-dithietans (57)—(59). However, the intermediacy of thioketones has been confirmed by u.v. spectrometry. The transient formation of thioketone and then its dimerization or a Diels-Alder reaction with an olefin has... 

Reaction scheme (f) has been most widely subscribed to by polymer chemists. In this writer s opinion it is not a likely pathway for reaction. The enthalpy change for dissociation of hexamer into monomer molecules, Eq. (7), is not known, but is probably on the order of 100 kcal/mole of hexamer, at a minimum. This, coupled with an unfavorable entropy effect, should make the free energy change for Eq. (7) so large (positive) that no reasonable assumption about the kinetic behavior of the various candidate species will suffice to make the concentration of monomer rate-determining. It must be recalled that the mass spectral data for ethyllithium vapor at 87° C failed to show the presence of any monomer. Intermolecular exchange of alkyl groups, observed in NMR studies of ethyllithium (47), almost certainly proceeds by dissociation of hexamer into tetramer and dimer. The enthalpy of dissociation of polyisoprenyllithium dimer has been estimated to be about 37 kcal/mole 31b). If a similar value obtains for short chain n-alkyllithium compounds (and there is reason to believe it does), the rate of formation of monomer could not possibly be as fast as the observed rates of initiation. Finally, it is difficult to see how a monomeric alkyl-lithium species could confer the required stereospecificity in reaction with an olefin 73). 

There are two proposed mechanisms for olefins methylafion [62] (1) a co-adsorbed mechanism in which methanol and an olefin are adsorbed on a single acid site and react in a single, concerted step and (2) a surface methoxide mechanism in which methanol or DME dehydrates to form a methoxide that desorbs upon reaction with an olefin. 

ROM-CM Sequence The ROM reaction of a cycloalkene engaged in the subsequent CM reaction with an olefinic partner provides the straightforward procedure for the synthesis of diene products having the isolated double bonds. This sequence is applicable not only to relatively strained cycloalkenes but also to unstrained compounds such as cyclohexene. The ROM-CM sequence of norbor-nene compounds or cyclopropene ketals with various olefins is reported for the preparations of natural products. 

The generation of an arylnitrene from an arylazide catalysed by an iron-tetracarbene complex has been highlighted as an efficient method to produce arylaziridines in a single step by reaction with an olefin. ... 

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