Terphenyl carboxylate

The terphenyl carboxylic acid derivatives have also been employed as supporting ligands in transition metal chemistry. For example, several binu-clear rhodium(II) terphenyl carboxylates (Fig. 20) have been reported.95 These were synthesized using the alternative route described in Eq. (8).96... 

An elegant and efficient approach for the synthesis of structural models of carboxylate-rich non-heme dinuclear iron proteins involves the use of bulky ligands of the terphenyl carboxylate family [47, 48]. The resulting dinuclear iron(II) complexes can adopt two conformations, called the windmill and the paddlewheel motif (Scheme 2.9). 

Scheme 2.9 Equilibrium between windmill (left) and paddlewheel (right) structures of dinuclear iron(ll) complexes comprising ligands from the terphenyl carboxylate family (Scheme 2.8b).

The failure to incorporate versatile functionalities on the internal position of the central m-terphenyl ring led to the development of two alternate routes to procure such compounds. Tuning and co-workers successfully worked out a protocol for lithiation of readily prepared iodides 24 and 28 [20]. Treatment of iodo derivative 24 with n-BuLi in the presence of Lil in cyclohexane gave the lithio derivative 52 as a white solid which on subsequent treatment with dry CO 2 in THF gave a 71% yield of the carboxylic acid 53 (Scheme 6) [20]. Also prepared by the same procedure is the isomeric tetramethyl-m-terphenyl carboxylic acid 55 which was obtained in 50% yield. Both 53 and 55 could be esterified in almost quantitative yields by diazomethane to give 54 and 56 respectively. Saponification of the esters back to carboxylic acids could be affected in excellent yields using Lil in pyridine (Scheme 6). 

Fig. 13. Chevron texture with typical transition bars observed upon cooling from the nematic state for polyester prepared from di-n-propyl-p-terphenyl-, carboxylate and tetrame-thylene glycol. Crossed polarizers. From ref. 20.

At present, only two organomagnesium derivatives of terphenyl ligands have been well characterized. However, the first terphenyl magnesium compound was reported more than 60 years ago with the generation of BrMgTriph in solution and its subsequent reactions to give the carboxylic acid, the acetyl derivative, and triphenylbenzophenone.28... 

Scheme 2.8 Examples of ligands used to model the carboxylate coreofcarboxylate-bridged dinuclearironenzymes (a) R3XDK[for R = CH3 H2XDK = m-xylenediamine bis(Kemp s triacid) imide] [57] (b) differently substituted terphenyl-based ligands (e.g. for R1 = CH3, R2 = H TolArCOOH) [48].

Diketones are synthesized by Claisen condensation of appropriate acetyl methyl ketone and ethyl perfluoroalkyl carboxylate. For example, 4,4/-bis(l",l,/,l//,2//,2",3//,3//-heptafluoro-4//,6//-hexanedion-6"-yl)-chlorosulfo-o-terphenyl (BHHCT) was synthesized from o-terphenyl by three step reactions (scheme 3 (Yuan et al., 1998a, 1998b)). The o-ter-phenyl are acetylated by acetyl chloride with anhydrous aluminum chloride as a Lewis acid and 4,4 -diacetyl-e>-terphcnyl is obtained. Then, the 4,4/-diacetyl-o-terphenyl is reacted with perfluoropropionic acid ethyl ester with sodium methoxide as a base. Finally, 4,4,-bis(l", 1",l//,2,2,3,/,3"-heptafluoro-4//,6"-hexanedion-6//-yl)-o-terphenyl is chloro-sulfonylatcd by chlorosulfonic acid to form BHHCT. 

A domino Knoevenagel/Diels-Alder epimerization sequence followed by Suzuki coupling provided a library of biphenyl and terphenyl spirocychc triones (Scheme 24) [58]. The initial Knoevenagel adducts 103 were formed from either 1,3-indandione or Meldrum s acid 101 and various bromosubstituted benzalde-hydes in the presence of catalytic (l)-5,5-dimethyl thiazolidinium-4-carboxylate (DMTC) in high yields. Diels-Alder cycloaddition of 103 with 104, formed in sim from 102 and (l)-DMTC, provided exclusively the cA-spiro compounds 105 due to epimerization of the minor trans isomer to the thermodynamically more stable cis. Subsequent Suzuki couplings of 105 with various boronic acids afforded the final compounds 106. 

Copolyesters containing two aromatic carboxylate residues have been synthesized, too. For example, 1,4-butanediol has been used with dimethyl terephthaiate in combination with a number of dimethyl esters, including dimethyl phthalate (4GP), dimethyl isophthalate (4GI), dimethyl sebacate (4G10), and dimethyl m-terphenyl-4,4"-dicarboxylate (4GTP). 

Ozonation of benzo[r,s,t]pentaphene (7) followed by oxidative workup led to benzo[r,s,t]pentaphene-5,8-dione (12) (14%), phthalic acid (13) (4%), p-terphenyl-2,2, 3, 2"-tetra-carboxylic acid-2, 3 -anhydride (14) (10%), and 2-(o-car-boxyphenyl)- ,10-phenanthrenedicarboxylic acid anhydride (15) (3%), with a 56% recovery of unreacted 7, Ozonation of pentaphene (11) led to a peroxidic mixture which on oxidative workup led to 2,2 -binaphthyl-3,3 -dicarboxalde-hyde (16) (16%), 2,2 -binaphthyl-3,3 -dicarboxylic acid (17) (16%), and 13 (2%), with a 28% recovery of unreacted 11. A comparison of the reactivity to ozone of carcinogenic polycyclic aromatics benzo c]phenanthrene (1), 7,12-di-methylbenz [a] anthracene (2), 3-methylcholanthrene (3), dibenz[si,]] - (4), and dibenzlsi, ]anthracene (5), benzo Si -pyrene (6) and 7, and the noncarcinogen 11, all determined in our laboratory, leads us to conclude that there is no simple, consistent correlation between carcinogenicity, K-and L-region additivity towards ozone and the Pullmans electronic theory of carcinogenesis. 

Yashima etal. [92] have designed and synthesized novel artificial double helixes, consisting of two complementary m-terphenyl-based strands intertwined through chiral amidinium-carboxylate salt bridges. Due to the chiral substituents on the amidine groups, the double... 

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