1.2.4.5- Tetracyanobenzene

Nakadaira and coworkers171 described the reaction of 6-trimethylsilylhex-l-ene with 1,2,4,5-tetracyanobenzene in which both the cyclic adduct 336 and the acyclic product 337 were formed (equation 32), and other workers further investigated the mechanistic details of this and related alkylations172. 

True CT complexes are formed between unsaturated electron acceptors, among which the derivatives with cyano and nitro groups predominate. The most common strong electron acceptors are 1,2,4,5-tetracyanobenzene, 7,7,8,8-tetracyanoquinodimethane (1), tetracyano-p-benzoquinone (2), tetracyanoethylene (TCNE) (3) and many electron-donor... 

Previously, Ohashi and his co-workers reported the photosubstitution of 1,2,4,5-tetracyanobenzene (TCNB) with toluene via the excitation of the charge-transfer complex between TCNB and toluene [409], The formation of substitution product is explained by the proton transfer from the radical cation of toluene to the radical anion of TCNB followed by the radical coupling and the dehydrocyanation. This type of photosubstitution has been well investigated and a variety of examples are reported. Arnold reported the photoreaction of p-dicyanobenzene (p-DCB) with 2,3-dimethyl-2-butene in the presence of phenanthrene in acetonitrile to give l-(4-cyanophenyl)-2,3-dimethyl-2-butene and 3-(4-cyanophenyl)-2,3-dimethyl-l-butene [410,411], The addition of methanol into this reaction system affords a methanol-incorporated product. This photoreaction was named the photo-NO-CAS reaction (photochemical nucleophile-olefin combination, aromatic substitution) by Arnold. However, a large number of nucleophile-incorporated photoreactions have been reported as three-component addition reactions via photoinduced electron transfer [19,40,113,114,201,410-425], Some examples are shown in Scheme 120. 

For non-electrophilic strong oxidants, the reaction with an alkane typically follows an outer-sphere ET mechanism. Photoexcited aromatic compounds are among the most powerful outer-sphere oxidants (e.g., the oxidation potential of the excited singlet state of 1,2,4,5-tetracyanobenzene (TCB) is 3.44 V relative to the SCE) [14, 15]. Photoexcited TCB (TCB ) can generate radical cations even from straight-chain alkanes through an SET oxidation. The reaction involves formation of ion-radical pairs between the alkane radical cation and the reduced oxidant (Eq. 5). Proton loss from the radical cation to the solvent (Eq. 6) is followed by aromatic substitution (Eq. 7) to form alkylaromatic compounds. 

In the second case, 2-tert-butyl dimethylmaleate (as a mixture of isomers) was obtained in 62% yield by a PET reaction between 2-tert-butyl-2-phcnyl-l,3-dioxolane anddimethylacetilendicarboxylate, catalyzed by 1,2,4,5-tetracyanobenzene(TCB) [80],... 

Bodige, S. G., Rogers, R. D. and Blackstock, S. C. (1997). Supramolecular networks via pyridine A-oxide C—H O hydrogen bonding in the crystal structures of 2,2 -dithiobis(pyridine A-oxide) and its complexes with 1,2,4,5-tetracyanobenzene and pyromellitic dianhydride. J. Chem. Soc., Chem. Commun., 1669. 

Bmax maximum field. DCNB p-dicyanobenzene. TCNB 1,2,4,5-tetracyanobenzene. At 2,4,6-trimethylphenyl group. See the reference(s) cited in this column. No MFE was observed. XnC=0 xanthone. MC=0 4-methoxybenzophenone. AcC=0 acetophenone. The magnetic field dependence of the MIE was observed. 

Taguchi M, Matsumoto Y, Moriyama M, Namba H, Aoki Y, Hiratsuka H. (2000) Effect of specific energy of heavy ions for 1,2,4,5-tetracyanobenzene radical anion formation. Rad Phys Chem 58(2) 123-129. 

The well known synthesis of low molecular phthalocyanines Pc, 2) starts from phthalic add derivatives like 1,2-dicyanobenzene, 1,3-diiminoisoindolenine and jAthalic anhydride The yield of metal free or metal containing Pc is often high (80-100%). By starting with a Wfunctional material like 1,2,4,5-tetracyanobenzene (TCB) or pyromellitic dianhydride (PMDA) a polymeric phthalocyanine (polyPc) (86) must be formed under the same conditions (Eq. 40). But the determination of structure and molecular weight is very difficult. Byproducts may be formed and the resulting polymers are often less soluble. But structure investigations are very important to correlate structure and property. 

TaMe 11. Results from mol mass detenninations (TCB 1,2,4,5-tetracyanobenzene PMDA pyromellitic dianhydride, TCP 3,3, 4,4 -tetracy-anodiphenylether, DCB 1,2-dicyanobenzene)... 

Table 13. Conductivity datas on some phthalocyanines (TCB 1,2,4,5-tetracyanobenzene, PMDA pyromellitic dianhydride). Measurements on compressed powders under vacuum...

One example of a dimeric subphthalocyanine has recently been reported. This macrocycle (2.332) was prepared by condensing of an excess of 4-r-butylphtha-lonitrile 2.278 with 1,2,4,5-tetracyanobenzene (2.331) in the presence of Ph2BBr. The resulting laterally bridged system 2.332 is obtained in 2.8% yield (along with a 24% yield of the monomeric subphthalocyanine 2.286) (Scheme 3.14). Despite the presumed non-planar nature of the subphthalocyanine units, H NMR data collected for this system indicate that it, like the monomeric systems discussed above, is aromatic. On the other hand, compound 2.332 displays spectral properties that differ dramatically from those of the monomeric macrocycle 2.286. For instance, compared to that of 2.286, the UV-vis absorption spectrum of 2.332 is rather featureless, although absorption bands are observed in nearly the same spectral region as in the case of 2.286. The emission spectrum of 2.332 also resembles that of the mono-... 

Charge-transfer complexes of neutral molecules in zeolites have also been examined. Transient experiments with 1,2,4,5-tetracyanobenzene (TCNB) as acceptor and arene donors have been reported. For naphthalene, transient absorption bands centered at 470 and 680 nm due to TCNB and naphthalene radical were observed [138]. The decay was found to be biphasic and was 10 times slower in dehydrated zeolite Y than in the hydrated sample, indicating a strong interaction with the framework. 

System 26 uses an extrinsic base to tune the reducing power of a-hydroxy radicals [181]. The photochemically generated diphenylketyl radical serves as De/Dp-H, Ae is 1,2,4,5-tetracyanobenzene (TCB), and Ap is a substituted pyridine (py). In the absence of the pyridine to facilitate PT, the ET reaction from the ketyl radical to TCB is endothermic by 0.4 eV. Consequently, the diphenylketyl radical decays slowly to reconstitute the starting reactants with no net reaction taking place. When coupled to PT by pre-associating the... 

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