Biphenylenes

Biphenylene underwent dimerization in the presence of phosphine complexes of Group 10 transition metals to afford tetraphenylene (2) [4]. Catalytic hydrogenation of biphenylene with phosphine complexes of rhodium, nickel, palladium, and platinum resulted in the formation of biphenyl (3) [5]. Hydrosilylation and hydroboratlon of biphenylene occurred in the presence of a palladium catalyst to give 2-silylbiphenyls and 2-borylbiphenyl 4, respectively [6]. Disilanes, a 

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Biphenylene is nitrated with nitric acid in acetic acid at C(2), and further nitration with mixed acid gives 2,6-dinitrobiphenylene. The relative rate was not determined. 

Similarly, p-biphenylene-bis(2-thiourea) (130) in methyl cellosolve gave N,N -p-biphenylene-bis(2-amino-4-R-thiazole) (131), in which R=t-Bu, Ph, n-dodecylpheny], and n-undecylphenyl (Scheme 63) (553, 599). 

Some biphenylene end-capped polyquiaolines have been used to make carbon-fiber rekiforced composites (102). However, properties of these composites dropped off significantly when oxidatively aged for 50—100 h at 316°C. 

Benzo[6]biphenylene [259-56-3] M 202.2, m dec >250. Purified by sublimation under reduced pressure. 

Biphenylene [259-79-0] M 152.2, m 152 . Recrystd from cyclohexane then sublimed in vacuum. 

Benzyne is capable of dimerizing, so that in the absence of either a nucleophile or a reactive unsaturated compound, biphenylene is formed. The lifetime of benzyne is estimated to be on the order of a few seconds in solution near room temperature. ... 

Hydrogenation of 5,10-diazabenzo[6]biphenylene with Raney nickel in hot ethanol gave 2-phenylquinoxaline in 78% yield (9). Similar hssion of the four-membered ring occurs with biphenylene itself and with substituted bi-phenylenes (5). 

The ice-cold fluoboric acid solution is added rather rapidly, with stirring, to the finished tetrazo solution, the temperature being kept below io°. A thick paste of 4,4 -biphenylene-bis-diazonium borofluoride forms. The mixture is stirred at io° for twenty to thirty minutes. It is then collected on a 19-cm. Buchner funnel, and washed consecutively with about 200 cc. of cold water, 200 cc. of cold commercial methyl alcohol, and 200 cc. of commercial ether the cake is sucked as dry as possible between washings. It is then dried in a vacuum desiccator over concentrated sulfuric acid (sp. gr. 1.84). The yield of the dry solid is 393 400 g. (68-69 Per cent of the theoretical amount). The product decomposes at 135-1370. 

Sales (Ref SO) used the biradical compounds, p,p -biphenylene-bis(diphenylmethyl),... 

The biradical catalysts described previously for double-base propints (Ref 80) are also effective for hydrocarbon propints. Table 34 shows how p,p,-biphenylene-bis(diphenylmethyl) compares to n butyl ferrocene as a catalyst in a carboxy-terminated polybutadiene. These catalysts are claimed to overcome all of the processing difficulties, chemical stability and volatility disadvantages attributed to catalysts based on ferrocene and carborane derivatives. Another somewhat similar functioning catalyst, the free radical compd, 2,2-diphenylpicrylhydrazyl,... 

The unsubstituted benzyne (8.26) from 2-diazoniobenzenecarboxylate can be trapped in the absence of a Bronsted acid as biphenylene, i.e., dimeric benzyne (8.30 Ford, 1971), or by cycloaddition to a 4-71 donor such as furan to give 8.31 (Stiles et al., 1963). 

Blackley548 measured the rates of deuteration of biphenylene, fluorene, tri-phenylene, and phenanthrene relative to o-xylene as 6.15 5.85 1.08 1.32, which is in very good agreement with the values of 8.80 7.00 - 1.14 which may be deduced from the detritiation data in Table 159, obtained using anhydrous trifluoroacetic acid. Aqueous trifluoroacetic acid (with the addition in some cases of benzene to assist solubility) was used by Rice550, who found that triptycene was 0.1 times as reactive per aromatic ring as o-xylene (cf. 0.13 derivable from Table 159) whereas the compound (XXXI) was 0.9 times as reactive as o-xylene. An exactly comparable measure is not available from Table 158, but dihydroanthracene (XXXII), which is similar, was 0.51 times as reactive as o-xylene and... 

Rates of detritiation of the 1 and 2 positions of biphenylene and the 5 position of benzo [bjbiphenylene by lithium cyclohexylamide at 50 °C relative to benzene have been determined as 490, 7.0, and 1,865, respectively and the enhanced reactivity of the position a to the strained 4-membered ring has been attributed to the enhanced electronegativity of the strained bridgehead carbon atom. The same... 

In dibenzothiophene-S,S-dioxide the S atom is in a ring, and hence more constrained. The yield of SOz in the radiolysis is linear with the dose to about 13 Mrad after which it levels off as in p,p -ditolyI sulfone. However, the yield of S02 in this case is much lower (a factor of 25) than in the case of p,p -ditolyl sulfone (G = 0.002 compared to G = 0.05). This stability of the dibenzothiophene sulfone could be partially due to back reaction to reform the parent sulfone and partially due to more efficient energy delocalization. The expected biphenylene product was not detected due to limitations of the analytical method. Bowmer and O Donnell70 studied the volatile products in y-radiolysis of dialkyl, alkyl aryl and diaryl sulfones. Table 2 gives the radiolytic yields of S02 and of the hydrocarbon products of the alkyl or aryl radicals. The hydrocarbon products are those obtained either by H atom abstraction or by radical combination. The authors69 suggested the mechanism... 

Only a few building blocks are available for the synthesis of ester-containing rigid mesogenic units, namely dihydroxy-, dicarboxy-, or (hydroxy, carboxy)-l,4-phenylenes, 4,4,-biphenylenes, and 2,6-, 1,4-, or 1,5-naphthylenes (Table 2.15). 

Bei der Reduktion von 1,2-Dibrom-benzocyclobuten wird als einziges Dimerisations-produkt 6a,lOb-Dihydro-(benzo-[a]-biphenylen) isoliert5 ... 

An alternative strategy for promoting Diels-Alder reaction by proton involves the activation of dienophile by hydrogen bonding [93]. Biphenylene diol 143 (Scheme 4.26) forms doubly hydrogen-bonded complexes with a,j]-unsaturated carbonyl compounds, which strongly accelerate the Diels-Alder... 

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