Tetraphenylethylene, reduction

Tetraphenylethylene Glycol. This prcp iration illustnites the mild conditions under which aryl ketones may undergo bimolecular reduction to com-... 

Other selected examples include tris(tetramethylethylene diamine-sodium)-9,9-dianthryl 143,154 alkali metal salts of 9,10-bis(diisopropylsilyl)anthracene 144,155 as well as the closely related naked 9,10-bis(trimethylsilyl)anthra-cene radical anion 145.156 This chemistry is further extended to the solvent-shared and solvent-separated alkali metal salts of perylene radical anions and dianions 146, 147,156 while other examples focus on alkali metal salts of 1,2-diphenylbenzene and tetraphenylethylene derivatives, where reduction with potassium in diglyme afforded contact molecules with extensive 7r-bonding, [l,2-Ph2C6H4K(diglyme)] 148.157 Extensive 7r-coordination is also observed in (1,1,4,4 tetraphenylbutadiene-2,3-diyl)tetracesiumbis(diglyme)bis(methoxyethanolate) 149.158... 

A further interesting point concerns unusually small differences between the reduction potentials of mono- and dianions of some molecules containing olefinic double bonds. Although in tr ns-stilbene the formation of the dianion occurs approximately 500 mV negatively to the radical anion formation [35, 120], for tetraphenylethylene the standard potentials for the R/R couple and the... 

Pairs of radical ions of like charge also react by electron transfer (i.e., they disproportionate). One classic example involves reduction of tetraphenylethylene and subsequent ET between two tetraphenylethylene anions. A more recent interesting example is that of cyclooctatetrene radical anion 148 . Alkali metals readily reduce the nonplanar cyclooctatetraene, generating a persistent planar radical anion... 

The polarographic reduction of tetraphenylethylene in dimethylformamide with n-BU4NCIO4 as a supporting electrolyte is an irreversible two-electron process. Preparative electrolysis in the same solution resulted in the formation of the dianion. The exocyclic bond of this dianion can be disrupted homolytically. Therefore, water treatment of the electrolyzed products leads to diphenylmethane (Wawzonek et al. 1965). 

Lithium organic compounds were obtained by 2e-reduction of 1,1-diphenyl-ethylene or tetraphenylethylene. The first olefin yielded quantitatively dilithio-1,1,4,4-tetraphenylbutane by dimerization of the intermediate radical anion (Eq. (244) ) whereas the second formed dilithiotetraphenylethane 62 2 K... 

This procedure is adapted from the method of Schlenk and Bergmann.3 Tetraphenylethylene has been prepared by the reaction of diphenylmethane with diphenyldichloromethane 4 by the reaction of diphenyldichloromethane with silver or zinc 4 by the reaction of thiobenzophenone with copper 6 by the reaction of diphenylmethane with sulfur 6 by the reduction of benzophenone with amalgamated zinc in the presence of hydrochloric acid 7 and by the rearrangement of 1,2,2,2-tetraphenylethanol with acetyl chloride.8... 

Reduction of 308 with sodium borohydride gives 24% tetraphenylethylene with lithium borohydride, 75% of 2,2-diphenylethanol and 16% of 2,2-diphenylethyl disulfide with di-isobutylaluminum hydride, 39% l,l,3,3-tetraphenyl-2-propanone and 30% of benzophenone. Lithium aluminum hydride gives four products that may be formed by way of cyclopropanone intermediates. ... 

The first experimental hint for a finite lifetime of an alkyl halide anion radical in homogeneous etheral solution was provided by Garst and coworkers in 1977. From the reduction of 5-hexenyl chloride, bromide and iodide with disodium tetraphenylethylene in 2-methyltetrahydrofuran (MTHF) at 20°C they concluded that radical anions R-X Na were involved and that the order of their stability was R-I Na" >R-Br Na > R-CrNa. ... 

Tetraphenylethylene is another example of a slow charge transfer. Here, the radical anion formation is fast, whereas the second charge transfer is slow [111]. In agreement with the thermodynamic findings, the second charge transfer suggests that considerable structural reorganization occurs at the activation barrier of the second reduction step. Nor... 

There have been few mechanistic studies of the one-electron reduction of ethylenes, but some conclusions have recently been drawn. Thus, the radicals formed from tetraphenylethylene and 1,1,3,3-tetraphenylbut-1-ene by the uptake of an electron (e.g. from sodium) are so sterically hindered that they do not dimerize but instead disproportionate to give the dianion and olefin (Bennett et al., 1964), e.g. 

The reduction of 55 with LiAlHa and subsequent acetylation afforded the diphenylmethyl thioacetate 150, while heating with copper powder in diglycol diethyl ether caused desulfurization to tetraphenylethylene 151 (Scheme 19) <1997H(45)507>. Treatment of 55 with a fourfold excess of (Ph3P)2Pt(77 -C2H4) in either THF or toluene solution yielded [Pt2(Ph3P)4(/i-S2)] and the platinum(O) compound 152 (Scheme 19) <2000ZNB453>. 

The resulting R- can suffer one of two fates, coupling with a polyacetylene radical or subsequent reduction to a carbanion, the latter affording reduction products. The mechanism is identical to that proposed for the reaction of disodium tetraphenylethylene with alkyl halides. - S... 

Stilbene is an unusual arene as a ligand in that it offers the possibility of coordination to an arene ring or to the double bond. In spite of the abundance of rare earth naphthalene complexes in hterature (Bochkarev, 2002 Bochkarev et al., 1997 Fryzuk et al., 2000), ( )-stilbene complexes are rare. Evans et al. reported the synthesis of [(C5Me5)2Sm]2((E)-stilbene) from the direct reaction of (C5Me5)2Sm and ( )-stUbene (Chart 23 Evans et al., 1990). Due to the poor quality of the crystal, the structure of the molecule could not be unambiguously determined but the authors suggested an unsym-metrical coordination mode based on coimectivity. The analogous samarium styrene and butadiene complexes (styrene complex shown in Chart 23) showed two-electron reduction of the C=C bond and concomitant oxidation of Sm(ll) to Sm(lll) (Evans et al., 2001). Related yttrium and lutetium complexes of the readily available tetraphenylethylene dianion have been reported with similar stmctural features (Chart 23 Roitershtein et al., 1998, 2004). 

---