Electron-transfer complexes substitutents

Silyl carbamates have recently been shown to undergo photoinduced electron transfer with substituted alkenes, in the presence of catalytic amounts of dicyanoanthracene and biphenyl (BP), to yield more complex carbamates182. Two examples which illustrate the complex structures created in good yield are shown in Scheme 61. 

Edwards, J. O., cd., Inorganic Reaction Mechanisms, Vol. 13 of Progr. Inorg. Chem., Interscience, 1970 (authoritative reviews on cobalt binuclear complexes, fast reactions, peroxide reactions, redox processes, electron transfer and substitution in square r/ complexes). 

Electrochemical studies of electron transfer promoted substitution on [Cr(CO)3(arene)] complexes have been conducted. The 1-e oxidation product [Cr(CO)3(arene)] reacts with PR3 to generate [Cr(CO)2(PR3)(arene)] . [Cr(CO)3(mesitylene)] reacts quantitatively with P(OBu)3 in propylene carbonate to form [Cr(CO)2 P(OBu)3 (mesitylene)]. At slow scan rates disubstitution is observed with P(OCH2)3CMe. Electron transfer ultimately gives [Cr(CO)2(PR3)-(arene)] (Scheme... 

Table 2 illustrates and scheme (13) explains the very variable rates of (electron-transfer catalyzed) substitution by TCNE in seemingly related carbonylmetal compounds, the manganese systems reacting faster by a factor of at least 10 than the pentacarbonyltungsten complex. 

Ru(NH3)4(phen)] and [Ru(NH3)4(phen-4-S03)] . The mechanism for formation of the latter, involving both electron transfer and substitution at the coordinated phen ligand, is unclear [Ru(NH3)4(phen)] " does not react directly with the sulfite radical anion. Substitution at ruthenium(II) plays a key role in the catalytic aerobic oxidation of cyclohexene by 2,2 -bipyridyla-quaphosphine complexes such as the [Ru(OH2)(bipy)2(PR3)] cations/ ... 

Some instances of incomplete debromination of 5,6-dibromo compounds may be due to the presence of 5j5,6a-isomer of wrong stereochemistry for anti-coplanar elimination. The higher temperature afforded by replacing acetone with refluxing cyclohexanone has proved advantageous in some cases. There is evidence that both the zinc and lithium aluminum hydride reductions of vicinal dihalides also proceed faster with diaxial isomers (ref. 266, cf. ref. 215, p. 136, ref. 265). The chromous reduction of vicinal dihalides appears to involve free radical intermediates produced by one electron transfer, and is not stereospecific but favors tra 5-elimination in the case of vic-di-bromides. Chromous ion complexed with ethylene diamine is more reactive than the uncomplexed ion in reduction of -substituted halides and epoxides to olefins. ... 

The symmetric series provides functional cyclohexadienes, whereas the non-symmetric one serves to build deuterated and/or functional arenes and tentacled compounds. In both series, several oxidation states can be used as precursors and provide different types of activation. The complexes bearing a number of valence, electrons over 18 react primarily by electron-transfer (ET). The ability of the sandwich structure to stabilize several oxidation states [21] also allows us to use them as ET reagents in stoichiometric and catalytic ET processes [18, 21, 22]. The last well-developed type of reactions is the nucleophilic substitution of one or two chlorine atoms in the FeCp+ complexes of mono- and o-dichlorobenzene. This chemistry is at least as rich as with the Cr(CO)3 activating group and more facile since FeCp+ activator is stronger than Cr(CO) 3. 

Mercuration of aromatic compounds can be accomplished with mercuric salts, most often Hg(OAc)2 ° to give ArHgOAc. This is ordinary electrophilic aromatic substitution and takes place by the arenium ion mechanism (p. 675). ° Aromatic compounds can also be converted to arylthallium bis(trifluoroacetates), ArTl(OOCCF3)2, by treatment with thallium(III) trifluoroacetate in trifluoroace-tic acid. ° These arylthallium compounds can be converted to phenols, aryl iodides or fluorides (12-28), aryl cyanides (12-31), aryl nitro compounds, or aryl esters (12-30). The mechanism of thallation appears to be complex, with electrophilic and electron-transfer mechanisms both taking place. 

Hoffman BM, Natan MJ, Nocek JM, Wallin SA (1991) Long-Range Electron Transfer Within Metal-Substituted Protein Complexes. 75 85-108 Hoffmann BM, see Ibers JA (1982) 50 1-55... 

The ability of compounds with double bonds to act both as electron donors and as electron acceptors in charge transfer complex formation is well known (81,82). Hammond (83) has studied the correlations of association constants and of the energy of the charge transfer absorption of 2-substituted-l,4-benzoquinones complexed with hexamethylbenzene with the Hammett equation. Charton (84) has studied the correlation with eq. (2) of association constants of 1-substituted propenes with Ag. ... 

As regards intimate mechanism, electron transfer reactions of metal complexes are of two basic types. These have become known as outer-sphere and inner-sphere (see Chapter 4, Volume 2). In principle, an outer-sphere process occurs with substitution-inert reactants whose coordination shells remain intact in... 

Electrogenerated monovalent Co complexes of the well-known open chain N202 Schiff base ligands salen (8), salphen (9), and their substituted derivatives undergo oxidative additions with alkyl halides. Reactions of the complex with substrates within the series RBr (R = Pr, Bu, t-Bu) proceed at different rates. The reaction occurs by an inner-sphere alkyl-bridged electron transfer, with a Co1- R+- X-transition state, which is sensitive to distortions of the complex in different configurations.124... 

Although somewhat more stable than its hexaammine relative, the air-sensitive [Co(en)3]2+ is still substitutionally labile and racemizes rapidly in solution. Chiral discrimination in its (racemic) solutions has been observed in outer sphere electron transfer reactions with optically active oxidants including [Coin(EDTA)], 209,210 [Cr(ox)3]3-,211,212 Co111 oxalate, malonate, and acetylacetonate (acac) complexes.213... 

The remarkable physical properties exhibited by the divalent macrobicyclic cage complex [Co(sep)]2+ (29) are unparalleled in Co chemistry.219 The complex, characterized structurally, is inert to ligand substitution in its optically pure form and resists racemization in stark contrast to its [Co(en)3]2+ parent. The encapsulating nature of the sep ligand ensures outer sphere electron transfer in all redox reactions. For example, unlike most divalent Co amines, the aerial oxidation of (29) does not involve a peroxo-bound intermediate. 

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