Triphenylmethyl analogs

The 9-phenylxanthyl radical is a resonance-stabilized triphenylmethyl analog. The corresponding carbonium ion and carbanion are also stabilized and can be prepared in sulfolane, so that A//het can be directly measured.The data for benzyl and t-butyl are obtained by measuring the reduction and oxidation potentials of the radicals in acetonitrile. The results show that C6H5CH2 and (CH3)3C are much harder than the 9-phenylxanthyl radical (the latter is just one of several studied with similar properties ). The solution hardnesses are then responsible for the difficulty in forming the ions in the benzyl and t-butyl cases, and the stability of the ions in the resonance-stabilized cases. The effect of the small hardness in the latter cases also is evident in the small bond energy for homolytic dissociation. 

Free radicals with resonance are definitely planar, though triphenylmethyl-type radicals are propeller shaped, like the analogous carbocations (p. 225). 

In the paper published in 1900, he reported that hexaphenylethane (2) existed in an equilibrium mixture with 1. In 1968, the structure of the dimer of 1 was corrected to be l-diphenylmethylene-4-triphenylmethyl-2,5-cyclohexadiene 3, not 2 [38]. Since Gomberg s discovery, a number of stable radicals have been synthesized and characterized, e.g., triarylmethyls, phenoxyls, diphenylpicryl-hydrazyl and its analogs, and nitroxides [39-43]. The radical 1 is stable, if oxygen, iodine, and other materials which react easily with it are absent. Such stable radicals scarcely initiate vinyl polymerization, but they easily combine with reactive (short-lived) propagating radicals to form non-paramagnetic compounds. Thus, these stable radicals have been used as radical scavengers or polymerization inhibitors in radical polymerization. 

The reduction of hydroxylamine by titanous salts in water produces the free amino radical, a reaction analogous to the formation of triphenylmethyl from the carbinol and a reducing agent.138 The amino radical will attack benzene to give diaminocyclohexadiene and di-(aminocyclohexadienyl) it converts cyclohexene into cyclohexyl-amine.139... 

Triphenylmethyl sodium and triphenylmethyl potassium conduct in liquid ammonia although they slowly react with that solvent.887 888 When the liquid ammonia is allowed to evaporate from a solution of triphenylmethyl sodium in ammonia, the residue is a colorless mixture of sodamide and triphenylmethane. The sodium-tin and sodium-germanium compounds analogous to sodium triphenylmethide are also strong electrolytes in liquid ammonia. Sodium acetylide in liquid ammonia is dissociated to about the same extent as sodium acetate in water.889... 

Whereas the synthesis of 2,2 -biimidazoles has been very well developed, that of 4,4 -biimidazoles has not. Pyne et al. revealed that the Pd(0)-catalyzed homocoupling of 4-iodo-l-(triphenylmethyl)imidazole (5a) or its 2-methyl analog 5b delivered the 4,4 -biimidazoles 6a and 6b, respectively [6],... 

This idea was based on the well-known analogous reactions of metal halides with triphenylmethyl halides, and thus seemed plausible. However, detailed studies have shown... 

Hydrogen chloride reacts in light to form triphenylmethane and triphenylcMoromethane. The reaction is reversible (Schlenk). NO, N02, and many organic radicles add themselves to triphenylmethyl. The combination with quinone is analogous (Schmidlin). 

Analog konnen auch leicht abspaltbare Alkyl-Gruppen in 1-Position wie die Methoxy-me-thyl-858 oder die Triphenylmethyl-Gruppe (s.S. 121) ausgetauscht werden. 

In the light of the more complete study of ring-halogenated triphenylchloro-methanes in this paper, the free radical hypothesis was back - if it ever was excluded in the previous paper - in the final discussion of the constitution of triphenylmethyl , now with two tautomeric triphenylmethyl radical structures in equilibrium with each other and the Jacobson dimer 1 (Scheme 2). Note that the radical was symbolized by an open valence (a thick line is used here for clarity). The strong results obtained with 3 (Scheme 1) were explained by removal of the quinoid bromine atom from 4 giving a radical 6 which tautomerized to the triphenylmethyl analogue 7. By analogy with the... 

Triphenylmethyl fluoroborate will also abstract a hydride ion from tri-carbonyleyclohexa-l,3-dieneiron to give the cyclohexadienyl complex [Fe(CO)3(C H7)] BF4 (5,9, 76), analogous to the cycloheptadienyl complex [Fe(CO)3(C7H9)l BF4 described above. 

Pyrroles, furans and thiophenes react preferentially with free radicals at the 2-position. Thus, reaction of pyrrole with benzyl radicals gives 2-benzylpyrrole. With triphenylmethyl radicals, pyrrole behaves like butadiene giving the adduct (163). /V-Methylpyrrole undergoes free radical benzoyloxyla-tion with dibenzoyl peroxide to give the 2-benzoyloxypyrrole (164) and 2,5-dibenzoyloxypyrrole (165). Furan, however, is converted in good yield to a mixture of cis and trans addition products analogous in structure to (163). 

The conversion of 4if-pyrans to pyrylium salts has also been accomplished. Thus, the ester (678) yields the 2,6-dimethoxycarbonylpyrylium salts (679 R = H or Me) on treatment with triphenylmethyl perchlorate in liquid sulfur dioxide (Scheme 272) (73ACS1385) and the amide (680) is formed in an analogous manner (74ACS(B)517). 

The analogous cycloheptadienyl complex (5 equation 1) was similarly prepared by Dauben and Ber-telli,4 but the acyclic pentadienyl systems were a little more difficult to obtain. The triphenylmethyl cation does not remove hydride from tricarbonyl(frans-pentadiene)iron (6 equation 2). The corresponding c/s-pentadiene complex (7 equation 3) cannot be prepared directly from the diene and an iron carbonyl,... 

AH attempts to convert dimer 263 into a dimeric 2-benzopyryIium salt, on treatment with triphenylmethyl or acetyl perchlorate, lead only to the rupture of the newly formed C—C bond and to the regeneration of the initial monomeric salt 261, unlike the behavior of dimers of monocyclic pyrylium cations [73DOK(212)370]. Dimerization may be considered a typical reaction for benzo[c]pyrylium-4-oxides of type 19, which react in dimerizations as 1,3-dipoles by analogy with their behavior in cycloadditions (Section III,E,2). 

In a number of ways the reactions of stable silylenes resemble those of phosphines, R3P, to which they are isolobal analogs. Examples are provided by the reactions of 59 with covalent azides. Phosphines are known to react with azides to give phosphineimines, Ph3P=NR. In similar fashion, 59 reacted with triphenylmethyl azide in THF to give the silanimine 72 as its THF complex (equation 109)148. This reaction provides a new method for synthesizing compounds containing Si=N double bonds, which have previously been made by salt elimination reactions375. 

Unlike the formally analogous, but in reality ionic, tetramethyl(triphenylmethyl)-nitrogen compound 3 of Schlenk and Holtz 4), tetraphenyl(triphenylmethyl)phos-phorane (23) was unambiguously proven to be a covalent compound 33). Alkinyl-tetraphenylphosphoranes 24 were prepared only many years later 37) and shown to be stable only below —20 °C. 

A somewhat analogous ion-radical reduction of carbonium ions to free radicals has been shown to occur (Conant and Chow, 48) in the reduction of various triphenylmethyl carbonium ions with chromous or titanous ion. 

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