Ethylene electron deficient

Silver is an important metallic catalyst for the selective oxidation of ethylene. The silver catalyst is used to selectively convert ethylene to ethylene epoxide, an important intermediate for antifreeze. Whereas the epoxidation of ethylene proceeds with high selectivity on oxidic silver phases, metallic silver surfaces give only total oxidation of ethylene. Electron-deficient O is created on oxidized silver surfaces and this readily inserts into the electron-rich ethylene bond. 

Ethylene disulfonyl-1,3-butadiene (43) is an example of an outer-ring diene with a non-aromatic six-membered heterocyclic ring containing sulfur. It is prepared by thermolysis of sulfolenes in the presence of a basic catalyst. It is very reactive [43] and even though it is electron-deficient, it readily reacted with both electron-rich and electron-poor dienophiles (Equation 2.15). 

Because the addition steps are generally fast and consequently exothermic chain steps, their transition states should occur early on the reaction coordinate and therefore resemble the starting alkene. This was recently confirmed by ab initio calculations for the attack at ethylene by methyl radicals and fluorene atoms. The relative stability of the adduct radicals therefore should have little influence on reacti-vity 2 ). The analysis of reactivity and regioselectivity for radical addition reactions, however, is even more complex, because polar effects seem to have an important influence. It has been known for some time that electronegative radicals X-prefer to react with ordinary alkenes while nucleophilic alkyl or acyl radicals rather attack electron deficient olefins e.g., cyano or carbonyl substituted olefins The best known example for this behavior is copolymerization This view was supported by different MO-calculation procedures and in particular by the successful FMO-treatment of the regioselectivity and relative reactivity of additions of radicals to a series of alkenes An excellent review of most of the more recent experimental data and their interpretation was published recently by Tedder and... 

With monosubstituted electron-deficient ethylenes, compound 123 gives a mixture of the exo and endo adducts (e.g., 124 and 125 R = CO2Me, CN, COMe). With styrenes the endo isomer (126) predominates. These adducts (126) are transformed into isomers 127 by trifluoromethanesulfonic acid. Ethyl vinyl ether gives exclusively the endo adduct (124 R = OEt). Similar... 

Complexes of Olefines and. Silver Ion.—Much work has been done on the interaction of the silver ion, Ag+, with unsaturated and aromatic hydrocarbons. (Mercuric ion and some other metal ions also react with carbon-carbon double bonde.) The structure proposed by Win-gtein and Lucas11 is probably essentially correct. Let us consider a silver ion and ethylene. The system is an electron-deficient one there are 12 valence electrons and 13 valence orbitals (including one orbital for the silver ion). We may write three structures for the complex ... 

The rates and orientation of free radical additions to fluoroalkenes depend upon the nature of the attacking radical and the alkene, but polar effects again are important For instance, methyl radical adds 9 5 times faster to tetrafluoroethylene than to ethylene at 164 °C, but the tnfluoromethyl radical adds 10 times taster to ethylene [7551 The more favorable polar transition states combine the nucleophilic radical with the electron deficient olefin 17 and vice versa (18) These polar effects account for the tendency of perfluoroalkenes and alkenes to produce highly regular, alternating copolymers (see Chapter starting on page 1101)... 

The analysis of the syn-addition of molecular fluorine to ethylene at the MP2/6-31 +G level with IRC calculations indicates that F2 approaches the C=C bond vertically at the middle to form a perpendicular complex 38 as the intermediate. The latter complex then re-orientates to a rhombic-type transition state 39 to give the final syn-addition product 4084. This analysis rules out the involvement of the square-type complex 41 proposed earlier. However, these calculations do not clarify the F2 addition to electron-deficient alkenes, such as acrylonitrile84. 

Using cheaper metals, electron-deficient imines such as sulfinylimine (20) can be reduced by diethylzinc, using a chiral nickel(II) catalyst yields and des >90% can be achieved.53 Interestingly, ketones are unaffected by the process many common reducing agents cannot so discriminate. XH NMR profiling indicates ethylene production, a... 

According to the rule formulated in [15], the combined a- and /1-effects (of fluorine substituents) imply that fluoroolefins will react with electrophiles so as to minimize the number of fluorines f to electron-deficient carbon in the transition state. In accordance with this rule, reaction of CH2=CF2 with HF starts as an attack of electrophile (H+) on the CH2 group of ethylene (Eq. 32, pathway A), since this process leads to carbocation 12 stabilized by two a-fluorines in contrast to the much less stable intermediate 13 containing two /1-fluorines and derived from the initial attack of H+ on the CF2 group of the olefin ... 

Such J-mctals as Cu(I) [but not Cu(II)], form a variety of compounds with ethenes, for example [Cu(C2H4)(H20)2]C104 (from Cu, Cu2+, and C2H4) or Cu(C2H4)(bipy)+. It is necessary to mention that, of all the metals involved in biological systems, only copper reacts with ethylene [74b]. Such homoleptic alkene complexes can be useful intermediates for the synthesis of other complexes. The olefin complexes of the metals in high formal oxidation states are electron deficient and therefore inert toward electrophilic reagents. By contrast, the olefin complexes of the metals in low formal oxidation states are attacked by electrophiles such as protons at the electron-rich metal-carbon a-bonds [74c]. 

Rhenacyclobutane complexes 110 can be synthesized by the [2+2] cycloaddition of ethylene with rhenium alkylidene complexes at low temperatures (Scheme 19) <1993JA2980>. However, even at low temperature, the alkylidene and rhenacyclobutane complexes combine to yield the rhenacyclic alkylidene 111 by an indeterminant mechanism. At room temperature, the most electron-deficient rhenacyclobutane 110c extmdes ethylene and reverts to the corresponding alkylidene complex. 

Another aspect of evolution of Pd catalysts during a reaction is the change in the electronic properties of palladium. Namely, both in the reaction of ethylene dimerization (in the absence of H2 in the gas phase) and in the reaction of CO with H2, drastic changes in the activity and selectivity during initial stage of the reaction were correlated with the fact of formation of electron-deficient Pd species. 

Sinn and Patat (59) drew attention to the electron-deficient character of those main group alkyls that afford complexes with the titanium compound. Fink et al. (51) showed by 13C NMR spectroscopy with 13C-enriched ethylene at low temperatures (when no alkyl exchange was observed) that, in the more highly halogenated systems, insertion of the ethylene takes place into a titanium-carbon bond of a titanium-aluminum complex. 

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