Biphenyl 2,2 -dianion

TABLE 5 Comparison of and C Chemical Shifts (in ppm) for the Coordinated Biphenyl Ring of M2K2-biph (M=Y, Sc, La, and Lu) and Literature Values Reported on Biphenyl Dianion Species (Using the Same Numbering Scheme as Table 4) (Huang et al., 2013) ... 

Biphenylf values are from Huber et al. (1981) Y2-bipb and Y-biph-Y values were adopted from Fryzuk etal. (1997), in which Y2-biph had two yttrium ions coordinated to the same ring of the 4,4 -dimethylbiphenyl dianion and Y-biph-Y had two yttrium ions on different rings of the biphenyl dianion. 

A series of luminescent platinum(II) complexes have been prepared with a biphenyl dianion (bph) as ligand (Fig. 3.7)S These complexes have the formulae Pt(bph)(Et2S)2, Pt(bph)(MeCN)2, Pt(bph)en, and Pt(bph)(py)2, and although they do not strictly have a nitrogen-based heterocyclic ligand, they are included here because their photophysical properties are in many ways analogous. The biphenyl dianion was chosen as ligand for these complexes because it contains an empty... 

Biphenylbis(tricarbonyt)chromium (l).1 Lithium anthracenide converts biphenyl complexed by two Cr(CO), groups into a fairly stable dianion of structure 2, in which two V-cyclohexadienyl anions are coordinated with Cr(CO)3. This dianion is alkylated by an alkyl halide to form 3, in which one benzene ring is... 

The addition of lithium to dicyclopropylacetylene (556) catalyzed by biphenyl (3%) in THF at —30 °C provoked a carbon-carbon bond cleavage in one of the cyclopropyl rings giving a delocalized dianion 557, which by reaction with dimethyl sulfate at —78 °C gave the aUtene 558 (Scheme 149). ... 

The trimethylsilyl radical produced either rapidly dimerizes or reacts with solvent so that very clean ESR spectra of the radical anion, with minimum interactions with the counterion, can be obtained (116). Further reduction to dianions is very slow, and exhaustive reduction to anion radicals minimizes problems associated with exchange between anion radicals and unreduced substrate (115). It now appears that the solvent HMPA greatly facilitates the one-electron reduction, not only for trimethylsilylsodium, but also for organolithium and magnesium reagents (110). It was found that 0.1F solutions of methyl-, n-butyl-, or f-butyllithium or benzylmagnesium chloride will quantitatively reduce biphenyl to its radical anion in less than 10 minutes (110). 

The expedient and regioselective metalation of unprotected biphenyl-2-, -3-, and -4-carboxylic acids has been reported.59 Unprotected biphenyl-2-carboxylic acid has been cleanly metalated with. sex-butyllithium at the position adjacent to the carboxylate and can then be subjected to site-selective electrophilic substitution (Scheme 8). The remote C(2 )-position has been attacked by the superbasic mixture of n-BuLi and t-BuOK (LICKOR) in THF or benzene. The resulting dianion cyclizes to give the fluorenone skeleton. The mechanism of the metalation of homologous compounds, 2-(pyridin-3-yl)benzoic acid derivatives, with strong bases has also been discussed.60... 

The high yield reduction of 1,2-dihalides to produce olefins has been employed to advantage to prepare reactive olefins. Electron transfer in electrochemistry is proportional to the diffusion coefficient, which is related in a much less sensitive way to temperature changes than is chemical reactivity. Thus it may become possible to synthesize and study electro-chemically species whose chemical reactivity is high by working at low temperatures. Electroreduction of 1,2-dibromobenzocyclobutene (144) in acetonitrile or butyroni-trile/TEAP or chemical reduction using the biphenyl radical anion resulted in the formation of benzocyclobutadiene (145)128. Efforts to observe the electrochemically generated anion radical or dianion of benzocyclobutadiene indicated that dimerization to 146 was faster than further reduction (equation 84). 

The 1,1,4,4-tetraphenylbutane disodium salt was found to eject electrons scavenged by added 1,1-diphenylethylene [59, 60]. In the case of trans-stilbene dianion, the photoejection of an electron was accompanied by isomerization in ds-stilbene radical anion while biphenyl was used as electron scavenger [61]. ds-Stilbene itself was used as scavenger of electron photoejected from aromatic radical anions like sodium perylenide [46], These scavenging experiments are... 

The reduction of PhsB is known to result in a radical anion PhsB- that is in equilibrium with the dimeric species [PhsB BPhs] ". However, if bulky substituents as in MessB are present and thus prevent attack of nucleophiles or dimerization, a blue-colored stable radical anion can readily be identified. While arylboranes are also known to form purple-colored dianions, the second reduction of simple triarylboranes is typically irreversible. In a recent study, Okada and Oda reported the formation of purple-colored solutions of dimesifylphenylborane dianions [Mes2BAr] (146 Ar = Ph, d-MesSiCeUi, biphenyl) upon extended reaction of Mes2BAr with Na K alloy in THE (Scheme 21). Formation of dianions was confirmed by multinuclear NMR specfroscopy. While the bulky mesityl groups provide chemical sfabihty to the dianions and thus prevent further chemical reactions, the presence of the unsubstituted phenyl group is beheved to allow for effective tt-interactions with the / -orbital on boron. 

The electrochemical behavior of two types of linked half-sandwich complexes appears to be influenced by structural changes which accompany the electron-transfer steps. The biphenyl complex (Cr2(CO)ft( 17, 17 -C12H10)] (11) is reduced in a reversible two-electron process at -1.61 V [versus Ag/AgCl, in tetrahydrofuran (THF) at 0°C] to a persistent dianion (28). The cyclic voltammetric peak separation of —35 mV argues against an interpretation involving two one-electron reductions to isolated redox sites (which would give a 60 mV peak separation) [vide ante (75)]. Rather, for the second electron transfer must be more positive than for the first, and the second reduction is, therefore, more facile than the first. 

The distinctive behaviour of lithium (and other alkali metals) with biphenyl towards i,4-dienones can be attributed to the more electropositive character of these metals, so that two electrons are transferred to give a dianion (54). Biphenyl... 

Ions and ion clusters may also donate electrons to the triple bond. Typical of aryl mono- and dianions are those of naphthalene and biphenyl (equation 81) Not... 

Two additional aryl crystal structures are noteworthy because they represent examples of alternative structural types of aryllithium anions. The first of these is the 2,2 -dianion of biphenyl (129). Hiis material is characterized as the bis-TMEDA solvate (130) with two lithium atoms doubly bridging the two car-banionic centers.Hie lithium atoms are located above and below the two aromatic rings. A completely different structure, depicted roughly as (131), is obtained for the air- and moisture-sensitive, violet crystals of dilithiobenzophenone. ... 

Polycyclic aromatics that have low reduction potentials are reduced by Li to give dilithium dianions. Among the more difficult to reduce members of this class that can react with Li are biphenyl and naphthalene " . Other substrates that are reduced to dilithium dianions are shown in Fig. 2. In addition, several benzo-, dibenzo-and tribenzoanthracenes and larger polycyclic aromatic compounds are reduced to dilithium dianions . 

This is achieved by flash-photolyzing a THF solution of Na , DD ,Na in the presence of a mixture of biphenyl and 1,1-diphenyl ethylene of known composition. Neither hydrocarbon reacts with the dianions, although both being at much higher concentration than Na , D D ,Na , Flash photolysis photo-dissociates some of the dimers into DTjNa" and then the equilibrium... 

ABA triblock copolymers cannot be produced by monofiinctional initiation when the A anion is not sufficiently basic to initiate polymerization of B monomers. In such cases the bifunctional initiators like alkali metal complexes of polycyclic aromatic compounds (e.g., naphthalene and biphenyl) can be used to produce ABA triblock copolymers. In these cases polymerization would be started with monomer B to produce a polymeric dianion which would initiate polymerization of the A monomer that is added later. The process is illustrated below for the commercially important styrene-butadiene-styrene (SBS) triblock copolymer ... 

Similar complexes have been prepared with biphenyl coordinated through two carbon atoms to a metal. The complex Pt(bphXbpy), where bph2- is the dianion of diphenyl, was prepared [40] in a similar way as Pt(ppy)2 from the 2,2 -dilithiobiphenyl [41] ... 

Ring A has also been expanded, with incorporation of C-19, by reduction of the 19-mesyloxy-l,4-dien-3-one (505) with biphenyl-lithium, an electron donor system. The mesomeric dianion (506) can expel the C-19 substituent to form either a 1, 19-cyclo- (507) or a 5, 19-cyclo-structure (508). The latter was isolated... 

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