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The e.s.r. spectra of a variety of alkyl radicals with α-halogen substituents have been examined in solution. The configurations of α-halogen substituted ethyl and β,β,β-trifluoroethyl radicals are correlated with the hyperfine splittings of α-methyl protons and α-trifluoromethyl fluorines, respectively. For an α-fluorine substituent, electronegativity plays an important role in determining the pyramidal configuration of the radical center, whereas size appears to be a more important factor with chlorine and bromine in promoting a less pyramidal configuration at the radical center. Two α-halogen substituents have a disproportionately greater effect than one halogen in influencing the configuration at the radical site. The g-factors of fluoroalkyl radicals are qualitatively analyzed in order to discuss possible mechanisms of β-fluorine hyperfine interactions and the effect of trifluoromethyl substitution on the configuration of the radical site.

Die bei Chloralkylradikalen wie z.B. dem β-Chlor-isobutyl- oder dem βββ-Trichlor- athylradikal auch bei -130 bis -140°C beobachtete 1,2-Chlorwanderung unter Bildung des tertiaren Isomeren bzw. des apgs-Trichlor-athylradikals wird bei homologen co,w,w-Trichloralkylradikalen auch bis 20°C nicht festgestellt.

Grignard reagents are coupled with alkenyl halides such as 1-bromopropene and P-bromostyrene in the presence of catalytic amounts of iron(II1) complexes to afford alkenes. This cross-coupling reaction can be employed as a synthetic route for alkenes, in which primary, secondary as well as tertiary alkyl groups like isopropyl, cyclohexyl, and tert-butyl Grignard reagents are utilized. The reaction is stereospecific since trans-1-bromopropene affords only transbutene-2 with methylmagnesium bromide and iron(II1) pivalate. Furthermore, the rearrangement of branched alkyl groups such as tert-butyl has not been observed with an iron catalyst. Among various iron(II1) complexes examined, tris(dibenzoylm'ethido)iron(III) is the most effective from the standpoint of rates and deactivation. Product and spectral studies suggest that the active catalyst is a labile iron species derived by reduction of iron(II1) in situ by the Grignard component. High rates of cross coupling are limited by deactivation of the catalyst due to an aging process attributed to aggregation of the active iron species. Several mechanistic schemes are considered for cross coupling including (a) oxidative addition of alkenyl halide to a low valent alkyliron species followed by reductive elimination of the cross-coupled product and (b) assistance by reduced iron in the concerted displacement of halide at the alkenyl center by the Grignard reagent.

The possibility of electron transfer being the initiation step in free radical pathways in oxidative addition is probed by exposing nickel(0) and platinum(0) species to a variety of electron acceptors; one-electron transformations are found to be facile in these systems.

The ESR spectrum obtained during the photolysis of Mn 2 (CO) 10 in tetrahydrofuran is assigned to a quartet state consistent with manganese(0) not manganese(II) species; the conclusion is supported by chemical studies.

The rates of the photochemical and thermal decarboxylation of aliphatic acids by lead (IV) tetraacete have been examined by a competition method. Photochemically, pivalic (tertiary) acid decarboxylates at 30° approximately 100 times, and isobutyric (secondary) acid 20 times, faster than n-butyric (primary) acid. The competitive decarboxylations of acids by lead(IV) carried out thermally at 80–100° show a smaller spread in reactivity. The thermal procedure is complicated by further oxidation of the olefinic products by Pb IV . Rates of decarboxylation are related to the multibond cleavage of the Pb-carboxylate linkages directly into alkyl radicals and carbon dioxide. The mechanism of the reduction of Pb IV is compared to the homolytic decarboxylations of the analogous Co III , Mn III and Ce IV carboxylates.

The alkylation of silver(I) trifluoromethanesulfonate by tetraethyllead is studied in a protic (acetic acid) and an aprotic (tetrahydrofuran) medium. Ethane is formed in acetic acid by protonolysis of the ethylsilver intermediate, but the reaction is no truly catalytic [as it is with copper(I)] due to the thermal instability of ethylsilver. The decomposition of ehylsilver in tetrahydrofuran can afford high yields of ethane or butane depending on the concentrations of the reactants. The formations of ethane and butane show different sensitivity toward molecular oxygen. The role of ethyl radicals generated by homolysis of the ethylsilver intermediate is discussed.

The addition of organostannyl, germyl, silyl and thiyl radicals to cyclopentadiene is examined by electron spin resonance. All of the adducts possess similar basic structures which are related to the cyclopentenyl radical but differ in their conformations. Heteroatoms consisting of tin, germanium and silicon in these adducts occupy an eclipsed position relative to the π-allylic framework, but these radicals do not have symmetrically bridged structures. Sulfur exhibits a smaller conformational effect, and the oxygen adduct is similar to the parent cyclopentenyl radical.

Cupric acetate, triflate and chloride are readily reduced to the cuprous salts by tetraethyllead in acetic acid solutions. Cuprous salts are subsequently involved in the catalytic process described previously, to produce ethane by the acetolysis of more tetraethyllead. The stoichiometry of the reduction step requires the consumption of two Cu II for each triethyllead acetate produced. The ethyl group which is liberated in the process can be quantitatively accounted for as ethylene, ethyl acetate or ethyl chloride. The latter are identical to the products obtained from the oxidation of independently generated ethyl radicals by the same Cu II complexes. The reduction of Cu II is suggested to proceed by alkyl transfer from tetraethyllead to form a metastable ethylcopper(II) intermediate, which subsequently undergoes rapid homolysis. The liberated ethyl radicals are efficiently scavenged by Cu II . The relationship of these organocopper(II) intermediates to those previously generated by the alkylation of Cu II by a variety of other alkylating agents in aprotic media is discussed.

The reaction between various Grignard reagents and silver(I) salts in the presence of nitrogen-containing oxidants such as lithium nitrate, nitrogen dioxide, and methyl nitrate has been examined in tetrahydrofuran solutions. Coupling dimer is formed in high yields almost independently of the structure of the Grignard reagent. From the stoichiometry, it is concluded that these oxidants oxidize two equivalents of metallic silver formed in situ to silver(I) species under proper reaction conditions. Other transition metal halides are also oxidized by these oxidants in a similar manner. Soluble forms of reduced silver complexes formed in the reaction of silver(I) nitrate and Grignard reagent are also described.

The carbon-13 NMR spectra of olefin—copper(I) complexes are examined. The change in the chemical shift of the vinyl carbon upon coordination is compared to the change observed in the proton spectrum. The Dewar—Chatt—Duncanson model for olefin—metal bonding is used to compare chemical shift changes observed in polyolefin and monoolefin complexes. The role played by π-back donation in the relatively large upfield shifts observed in monoolefin complexes is described. The use of copper(I) triflate as a CMR shift reagent for olefins is suggested.

The reactions of transition metal halides (Mn, Fe, Co, Ni, Pd, Cu, and Ag) with the low-molecular-weight alkyl Grignard reagents in tetrahydrofuran and diethyl ether, especially in the presence of styrene were reinvestigated. An alkyl transition metal species formed in situ by metathesis decomposed to a dialkyl (oxidative dimerization) or to an alkene and an alkane (oxidative disproportionation). Silver(I) and copper(II) were particularly effective in oxidative dimerization of primary alkyl groups. Alkyl groups which contain no β-hydrogen were also coupled by iron, cobalt, nickel, palladium, and copper(I) halides with varying degrees of efficiency. Oxidative disproportionation was generally the more common route to decomposition for alkyl groups which have β-hydrogens. It seemed to proceed directly via a bimolecular interaction of alkylmetals or indirectly by elimination of a hydrido-metal species. If the latter added to an alkene reversibly, exchange was observed between Grignard reagent and alkene. Styr...