Benzoquinones, , complexes

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. ... 

THPROL. Thiamine picrolonate dihydrate thiamine 3-methyl-4-nitro-l-(p-nitro-phenyl)-2-pyrazolin-5-onate dihydrate [C12H17N4OS+, C10H7N4O3 , 2(H20)]. Shin W, Pletcher J, Blank G, Sax M (1977) J Am Chem Soc 99 3491 THYBNZ10. Thymine-p-benzoquinone complex (C3H6N202, C6H402). Sakurai T, Okunuki M (1971) Acta Crystallogr, Sect B 27 1445... 

In contrast to the discrete complexes formed by organometallohgand (62), the benzoquinone complex (59) is geometrically prevented from chelating a metal ion and instead... 

The catalytic cycle of the palladium-catalyzed diacyloxylation follows the cycle depicted in Scheme 8-6 (X = RCOO, Y = R COO ). The coordination of a quinone in the Ji-allyl)palladium intermediate was demonstrated by NMR studies including T, measurements [58]. Attack by the second nucleophile results in the formation of the 1,4-addition product and a palladium(0)-benzoquinone complex. In an independent mechanistic study, it was shown that such Pd(0)-benzoquinone complexes, which are stable at neutral conditions (pH 7), react with weak acids to give hydroquinone and the palladium(II) salt of the acid [Eq.(36)] [59],... 

In the palladium-catalyzed 1,4-oxidations of conjugated dienes described so far, only heteroatom nucleophiles have been employed. There is an intrinsic problem in using free carbanions in an oxidation reaction since the oxidant can readily remove an electron and oxidize the carbanion to a radical. Furthermore, in the procedure associated with the best selectivity, i.e., the benzoquinone-based process, acid is required to regenerate the Pd(0)-benzoquinone complex to Pd(II) and hydroquinone. 

A thermal, Lewis acid-catalysed [3+2] cycloaddition of allylsilanes giving the dihydrobenzofurans 57 has also been described (equation (3)) (02TL5349). The mechanism has been interpreted in terms of formation of a p-silyl cation by a zinc-benzoquinone complex, followed by cyclisation, and elimination of isobutene when R = Bu. 

Tetrachloro-p-benzoquinone)) Complex 631- Copoly(Ethylene - Tetrafluoroethylene) o 631-2953... 

Poly-jp- Phenylenediamine) - (2,3,5,6-Tetrachloro-p-benzoquinone)) Complex (Poly-(p- Phenylenediamine) - (2,5- Cyclohexa--diene Dimalononitrile)) Complex (Poly-(p- Phenylenediamine) - Ethenetetracarbonitrile) Complex... 

The re-oxidation with quinone can occur by several mechanisms. The re-oxidation of Pd(0) by quinone in acid has been studied by Backvall. This work showed that the well-known quinone complexes of Pd(0), such as the Pd(COD)(benzoquinone) complex in Equation 16.128, react with acid to protonate the oxygen of the quinone. A second protonation... 

CpCo(n -benzoquinone) complexes from which the ligand may be easily... 

Cobalt, Rhodium, and Iridium. —Cations of structure [Co(diene)(PRs)3]+ have been prepared (diene = butadiene or isoprene) they are fluxional in solution, but low temperature n.m.r. spectra indicate a square pyramidal structure with diene in the basal plane. The benzoquinone complex (87) has been prepared and undergoes successive mono- and di-protonation at oxygen methylation with Mel also occurs at oxygen to yield (88). Cobaltacyclopentadiene complexes Cp(PPh3)Co(CRi=CR CR =CR ) (RSR =Me, Ph, or CO Me) react with... 

---